Category Archives: Agriculture

Self-compatibility is controlled by a single self-compatibility Sf dominant allele

Wide cultivation of almond, often under the more severe environments of Central Asia and the Mediterranean region, was possible because of the availability of a highly diverse gene pool, genetic recombination promoted by its self-incompatibility, and possibly, by interspecific hybridization and gene introgression involving other members of the Amygdalus subgenus. As a result, almond is an extremely variable species, with a high morphological and physiological diversity. This variability, measured with biochemical and molecular markers , has revealed that almond is the most genetically variable of the diploid Prunus cultivated species. In the Mediterranean Region, 2000 years of almond culture concentrated production to specific areas, where well-defined seedling ecotypes and local cultivars evolved. By the turn of the 20th century, most of these almond-producing countries had identified locally desirable cultivars that were often seedling selections of unknown origin. Thus, growers selected cultivars and landraces, which represented a rich genetic diversity. Most of these Mediterranean local cultivars have largely disappeared from cultivation in the last 50 years. Modern almond cultivation is based on a reduced number of cultivars grafted onto soiladapted clonal root stocks and cultivated under irrigated conditions when possible. Modern almond breeding started in the 1920s with the making of controlled crosses and seedling selections to meet changing agronomic and market demands. Currently,growing blueberries there are six active public breeding programs worldwide: the USA , Spain , Australia , and Israel .

Some private breeding programs exist also in the USA. In addition, there were various breeding initiatives in Russia, France, Greece, Italy, and Argentina. Different breeding objectives were developed according to regional agronomic, commercial, and market requirements. One of the main differences in the objectives is nut shell hardness. Two types of almonds are bred: soft-shelled and hard shelled . Common aims of Mediterranean breeding programs are self-compatibility and late-blooming, as most traditional almond cultivars are self-incompatible and early blooming.During the last 50 years, almond breeding for self-compatibility has mainly used two sources of Sf, local landraces originated in Italy and related species such as P. persica and P. webbii. Almond breeders have relied mainly on out crossing and, occasionally, on introgression from other Prunus species, for the development of new cultivars. Initially, in the USA and later in Russia and Mediterranean region , rapid genetic advances were achieved. In California, “Carmel” , as “Nonpareil” pollinizer, was the first cultivar release with extensive commercial impact. In Russia and the former Soviet Union, several late-flowering and frost-hardy cultivars were obtained in the 1950s with Primorskyi later used extensively for breeding in Europe. In the Mediterranean region, late flowering, productive, well-adapted, and resilient cultivars like Ferragnès or Masbovera were released with great success. The French self-compatible cultivar Lauranne showed a broad environmental adaptation, high production, and regular cropping. Although improved cultivars continued to be released, the amount of progress per generation diminishes since parents were continually drawn from the same gene pool. This situation has resulted in a potential loss of genetic variability in new breeding stocks and cultivars. Inbreeding depression in almond, expressed as low vigor, reduced flower number and fruit set, increased fruit abortion, lowered seed germination and seedling survival, increased leaf and wood abnormalities, and loss of disease resistance have been reported.

In addition, low self fruitfulness in self-compatible almond genotypes was suspected to be due to inbreeding. Regarding breeding for self-compatibility, male parents carrying the Sf allele and sharing the other S allele with the female parent are commonly used. In addition, crossing heterozygous self-compatible parents in breeding programs has been suggested to obtain homozygous self compatible genotypes to be used in further breeding. Such breeding strategies can narrow the genetic variability of crops when they lead to a reduced number of genotypes utilized as parents. Summarizing, modern almond breeding and production are dominated by a small number of widely distributed and related cultivars. This situation can lead to a potential increase of inbreeding depression and genetic vulnerability, i.e., susceptibility of most of the grown cultivars to biotic and abiotic stresses due to similarities in their genotypes. Therefore, it is needed to have up-to-date information of the relationships among genotypes used at breeding and production levels. Several almond populations have been analyzed with molecular markers in order to determine genetic variability and relatedness. However, these studies were performed with material from limited geographic areas and do not represent the current worldwide status of almond breeding stocks. Although genomic measures of inbreeding are more accurate than those obtained from pedigree data, pedigree-based analysis is a cost effective technique to estimate these parameters inbreeding populations and an alternative when genomic measures are unviable. Several reports have evaluated inbreeding based on pedigree data in breeding populations of fruit and nut tree crops. In almond, a pedigree analysis of 123 different genotypes from the USA, France, Spain, Israel, and Russia was reported. However, their work was mainly focused on North American genotypes and did not include many cultivars that have subsequently been released worldwide.

This study aimed to determine the genetic structure of current breeding stocks and breeding tendencies over the last 50 years using marker-verified pedigree data.Pedigree data of 220 almond genotypes were compiled from available bibliography and breeding records. From the 220 almond genotypes, 37 genotypes were no longer available as they were eliminated some time ago or were from discontinued breeding programs. To verify parental relationships of the rest of genotypes , we used SSRs, SNPs, and self incompatibility S-allele data from previous studies performed by the breeding programs taking part in this study . Marker data confirmed both parents of 71 genotypes and one parent of four genotypes and found three erroneous parentages. Two wrong parentages were found on the male parent of “Capella” and “Davey”, changing their pedigree to open-pollinated and a third incorrect parentage on “Yosemite” female parent, eliminating this genotype from the analysis. After the corrections made, pedigrees of 169 genotypes of known origin were analyzed . The origin of the genotypes were 59 from Spain, 56 from the USA, 16 from Russia, 11 from Israel, 10 from France, 7 from Australia, 7 from Greece, 2 from Argentina, and 2 from Italy. A pedigree data file was created. Each record in the file contained one cultivar or selection name, the female parent and the male parent, in that order. Once entered,square plant pots these data were available for inbreeding analyses such as determining the number of times a cultivar appeared in a pedigree as a male or female genitor. Genotypes of known origin were classified into two groups according to self compatibility: 104 self-incompatible and 65 self compatible.In summary, the inbreeding coefficient measures the probability that two alleles in a locus are identical by descent and so copies of the same allele from a previous generation. The pairwise relatedness measures the probability that two alleles at any locus are identical by descent between two different individuals. F and r range from 0 to 1, with values close to 0 indicating a low degree of inbreeding or relatedness and values close to 1 indicating a high degree of inbreeding or relatedness. The genetic contribution estimates the proportion of genome that comes from the same individual. Thus, a child will have 0.5 genome of either parent and a grandchild will have 0.25 genomes of his grandparents.To calculate F, r, and GC, parents of unknown origin were assumed to be unrelated and noninbred. The seed parent involved in all open pollinations was also assumed to be unrelated to the pollen parent. These assumptions, based on the fact that most almond cultivars are obligate out crossers because of their self-incompatibility, may lead to an underestimation of inbreeding. In the cases of genotypes of open-pollinated origin , numbers OP1, OP2, and OP3 were given to the pollen parent in order to be distinguishable for genetic studies. Also, all mutants were considered to have no genetic differences from the original cultivar, thus GC = 1. Since the differences between such mutants and the original cultivar are expected to be caused by a few mutations in the DNA, this simplification avoids the overestimation of inbreeding coefficients. Cultivars like Supernova and Guara were considered as “Tuono” clones. Regarding the different clones of the French paper-shell cultivar Princesse, used in both the USA and Russian breeding programs, we adopted the approach of Lansari et al.by analyzing both clones as the same cultivar. Historical reports suggest that the Hatch series “Nonpareil”, “I.X.L.”, and “Ne Plus Ultra” were seedling selections from an open-pollination progeny of the early-introduced cultivar Princesse.

This cultivar probably originated from the Languedoc region in France. Also, “Nikitskij” was selected in France in 1902. Because their specific origins remain uncertain, we analyzed these genotypes as nonrelated, which, however, could lead to an underestimation of inbreeding. Pedigree data were analyzed at four levels: worldwide, by country , by breeding program , and by genotypes carrying the Sf allele for self-compatibility.Our genetic study of almond breeding programs worldwide demonstrated that the most widely used cultivars were Nonpareil, Tuono, Cristomorto, and Mission. “Nonpareil” had a large influence in USA and Australian programs, where soft-shelled nuts are bred. This reference cultivar was present in all the breeding programs studied . The self-compatible “Tuono” and the late blooming “Cristomorto” were extensively used in the Mediterranean programs, where hard-shelled nuts are bred. “Mission” initially showed a considerable importance worldwide, but deeper analysis demonstrated that it was mainly influential in private American programs. Taking into account these results, we can establish two main breeding lines based on the use of three different founders: the European programs based mainly on “Tuono” and “Cristomorto” , and the North American–Australian programs based on “Nonpareil” . The French and Spanish breeding programs were based directly on “Tuono” and “Cristomorto”. In the French INRA program, the Italian cultivars Tuono and Cristomorto account for 60.0% of total GC and were present in the pedigree of all ten cultivars and selections evaluated. Also, the local French late-flowering and Monilinia-resistant cultivar Aï was a parent to both “Ferragnès” and “Ferraduel”. In the three Spanish breeding programs, the importance of “Tuono” and “Cristomorto” cultivars was very high, accounting to 46.2% of total GC. These two cultivars were present in the pedigree of 53 out of 59 cultivars and breeding selections from Spain. These results can be explained by the large influence of the French germplasm on the Spanish breeding programs, causing a high relationship between the programs of both countries . In the North American breeding programs, “Nonpareil” accounts for 43.7% of the total GC and was present in the pedigree of 48 out of 56 cultivars and breeding selections from the USA. In Australia, ‘Nonpareil’ accounts for 39.3% of the total GC and is present in the pedigree of 6 out of 7 cultivars and breeding selections. Also, “Lauranne” reaches an importance similar to ‘Nonpareil’, explaining the close relationship between the Australian and French programs . Even in other countries with noncontinuous breeding initiatives, such as Russia, Greece, or Argentina, the use of “Nonpareil” as a founder was common. Israel was the only country where these cultivars had a relatively low influence. This may be due to the extreme Israeli climatic conditions, forcing breeders to use locally adapted selections as parents. In Spain, the use of locally adapted cultivars such as Bertina at CITA as a donor for Polystigma ochraceum Sacc. resistance was successful but used only to a limited extent. Other examples of secondary founders include “Primorskyi”, used regularly as late-blooming and Fusicoccum-resistance donor in two of the Spanish breeding programs and “Eureka” and “Harriott” in the North American breeding programs.Pedigree analysis is a cost-effective and well-established way to monitoring inbreeding and relatedness among controlled breeding populations. However, the veracity of any analysis based on this kind of data relies on the accuracy of records collected across multiple institutions and by many breeders. In order to verify parental relationships of the genotypes under study, we used SSRs, SNPs, and self-incompatibility S-allele data from previous analysis carried out by the breeding programs taking part in this study. Our molecular marker analysis confirmed 146 parentage relationships and found three errors , which were corrected accordingly. Thus, the marker-based pedigree analysis performed showed only small parental changes and corroborates the consistency of the results reached by this study.However, several reports have demonstrated that large scale genomic analysis may provide more accurate results than pedigree analysis. This kind of genome-based pedigree analysis has already been performed in apple.

Similar marginal voids can also be seen in WT meristems treated with exogenous cytokinin

Although cytokinin responses are homogenously distributed in these meristems, the pWUS:eGFP-WUS pattern does not clearly show strong WUS expression in the peripheral regions where cytokinin induced stability might be expected. The results of cycloheximide and MG132 treatments do not help clarify this situation, as the alternating patterns of stability and instability cannot easily be explained in terms of the cytokinin signaling pathway alone. To do so requires assuming that the cytokinin phosphor-relay system has a previously undetected branch pathway, potentially regulating a protease with equally unusual phospho-dependent activity. However, this model is not much different than the observation that cytokinin influences WUS stability through both protein translation protein pathways, as both models require multiple steps with poorly known intermediates. Attempts to identify the possible intermediates using lists of cytokinin-targeted genes do not clearly help resolve this situation, as a meta-analysis found only five translation related genes, two of which modify mRNA, one that modified tRNA, and two that are involved with ribosomal RNA processing. The same list of cytokinin targets also contains six protease genes , while a single representative from the ubiquitin/proteosome pathway was down-regulated. In the absence of a clearly direct cytokinin-WUS connection, it is quite tempting to speculate that protein stability is a secondary effect of cytokinin responses. If so, stability may be a generic feature of cytokinin responses, which has the potential to affect all proteins simultaneously. Experiments with auxin on the other hand, suggest a much more direct link with WUS stability. Four hours of exogenous NAA treatment dramatically reduced pWUS:eGFP-WUS fluorescent levels,pot blueberries while comparable treatments with cytokinin took a minimum of 12 hours to show the slightest response in WUS expression.

The auxin–induced degradation was also readily blocked by cycloheximide treatments , indicating that the response requires protein translation. Still, exactly which proteins are translated, and how they affect WUS stability is not clear. Auxin induced degradation may have a functional significance for lateral anlagen though, as the concentration of auxin responses in distinct foci, would help rapidly reprogram the anlagen cells by degrading conflicting developmental proteins. This hypothesis is consistent with the large marginal voids of WUS and CLV3 expression found when cytokinin responses are ectopically induced with the pCLV3:GR-LhG4 x p6xOP:ARR1ΔDDK-GR system , which were often correlated to the presence of leaf primordia and sites of auxin accumulation.Although not quite as direct, other research has also shown that WUS transcript levels are indirectly linked to auxin transport. In addition callus tissue studies have found that induction of SAMs does not require cytokinin alone, but instead requires an appropriately high concentration of auxin or a balanced auxin/cytokinin ratio, clearly implying that auxin is a significant part of the process. Considering the overall organization of the SAM, this suggests a model where WUS helps stabilize the mutually exclusive pattern of auxin and cytokinin responses in the PZ and RM by activating the biosynthesis of both hormones and auxin transport genes within the CZ. The lack of hormone responses in the very cells that produce them is consistent with a similar pattern in root development, and given the often symplast-like environment in the SAM, a repressive mechanism may be necessary to prevent hormone response proteins from spreading into the CZ and suppressing biosynthesis. The fields of protein stability and instability brought about by the hormone responses also appears to define the number of WUS producing cells, and eventually, the concentration of WUS molecules that reach the CZ, forming an indirect, but stable set of feedback loops that share WUS as an anchor.

The CLV3 pathway may represent another feedback loop within this framework, as it is also activated by WUS in the CZ, similar to the postulated activation of hormone biosynthesis genes. Although the intermediate steps are not clear, CLV3 appears to suppress cytokinin-induced proliferation, as seen by the hypersensitive response of clv3-2 mutant to exogenous cytokinin . By doing so, it may potentially function as a third feedback loop, negatively regulating WUS transcription though a mechanism that is slightly more direct than either hormone pathway alone. It would thus be of great interest to learn what proteins regulate WUS transcription in the RM, as the ahk2/3/4 RNA in-situ clearly shows that cytokinin responses are not involved.Meristems used for nuclear/cytoplasmic measurements were stained with FM4-64 and DAPI to help delimit cell walls and nuclei, respectively. Cell volume was assumed to be cubic rectangular, and estimated by calculating depth as an average of length and width measurements. Nuclei were assumed to be spherical, and their volumes were calculated directly from their maximum cross-sectional diameter. The relative concentration of fluorophores in each subcellular compartment was then estimated by sampling a representative volume to calculate the average concentration in “fluorphore units/µM3 ” units, based on the voxel dimensions in the optical section. This figure was then multiplied by the volume of each subcellar compartment to estimate the relative amount of fluorophore units present in each. At least 4 cells from each of three tissue layers were sampled in each meristem, and a minimum of 5 meristems were sampled for each treatment, for a total of 180 measurements. In May 2016, an environmental scientist at the Indian Institute of Science, T.V. Ramachandra, made headlines with his assertion that Bengaluru 1 — the center of India’s information technology boom and one of its fastest growing cities—would be “dead” in five years . The claim struck a nerve, and led to a series of English medium news articles and social media posts debating Ramachandra’s statement . As evidence of its continuing resonance, the discussion again surfaced in August 2017, with headlines proclaiming Bengaluru’s demise in three years . Although Ramachandra’s contentious argument was based on his study about environmental degradation in the city , he expressed the effects of this decay in terms of food and urban life.

He is quoted in Deccan Herald as saying, “what’s the point [of] earning better when the food that you eat is adulterated? As a result of unplanned urbanisation, Bengaluru is going to be an unliveable and dead city in the next five years” . With this bleak prediction, Ramachandra challenged narratives proclaiming the economic advantages of rapid urban development—higher wages and a burgeoning middle class—by suggesting that money means little when one’s food is inedible and the urban environment is uninhabitable. Ramachandra’s assertion and the intense debate that it inspired are indicative of the broader insecurities and aspirations that anchor this dissertation. I trace the shifting food supply chain that connects Bengaluru with its agrarian periphery in order to understand the changing relationships among food producers and consumers in the context of rapid urbanization. With analmost 47% urban growth rate between the 2001 and 2011 , Bengaluru and its outlying communities have changed drastically since the start of the city’s information technology boom in the early 1990s. As the city expands and its landscapes and livelihoods shift, urban residents express regret at the loss of the calm and idyllic “Garden City,” replaced by unhealthy ecologies and human communities. But, they also proudly proclaim Bengaluru to be a “cosmopolitan” city, with restaurants and bars befitting a globally connected technology hub. This ambiguous relationship with Bengaluru’s shifting food scene extends to the edges of the city, where farmers whose fields sit alongside factories and housing developments are in an economically and environmentally precarious position, and who recognize that they are likely the last generation to farm their land. They are also aware, however, that their proximity to the city opens up new opportunities, including higher prices for their commodities,square plastic plant pots access to private schooling for their children, and the potential to sell their land at a great profit to real estate developers. Food, a daily need packed with political and cultural meaning, is a particularly productive site of analysis to discover how processes of production, exchange, and consumption intersect with the insecurities and aspirations of an expanding cityscape. This project analyzes the relationship between food supply chains and the city. Tracing food networks illuminates shifting desires and consumption patterns as well as changing relationships among urban and agrarian communities. Examining how the expanding city affects food supply chains sheds light on how changing livelihood structures, infrastructures, and class relationships intersect with issues such as food safety and access. How food is produced, exchanged, and consumed can tell us about the relationship between bodies and changing cityscapes. Advocates of the second intervention that I consider in detail in this dissertation understand their project as a challenge to corporate assertions about the efficacy of “direct” supply networks. Increasingly, urban middle and upper class residents of Bengaluru are growing their own food for home consumption. For these individuals, gardening offers two interventions: one, a way to ensure food quality and safety in the context of increasingly untrustworthy food sources; and two, a site to contest the social and environmental ills of urban development. In asserting the value of food cultivation among urban professionals, Bengaluru’s middle and upper class gardeners generate new understandings and practices of contemporary urban life. However, these projects remain anchored in existing class and caste inequalities that make cultivation a leisure activity for some and a livelihood strategy for others.

The stakes for these projects are high—while they are guided by the concerns and desires of a particular class segment , they have repercussions for the entire food system and thus affect everyone. It is therefore critical that we understand these projects, as ideological forms and concrete practices that promise to shape Bengaluru’s food ecologies going forward. What is lost by focusing on some problems and ignoring others? What solutions emerge to answer these problems? Whom do these solutions benefit, both intentionally and otherwise? It is critical to consider these questions because the rate of urbanization worldwide has generated multi-fold challenges for ensuring food security, sustainability, and safety. Yet the effects of urbanization on food systems remain understudied . Feeding the world’s growing cities is of pressing concern as farmers abandon agriculture in the face of mounting economic insecurity and climate-related instability. This dynamic is particularly pressing in India, where UN-Habitat’s 2016 World Cities Report predicts that the urban population is expected to grow by an additional 300 million residents by 2050. In this context, a primary concern is feeding the burgeoning urban population while also ensuring food security for rural communities. Hunger and malnutrition remain critical struggles in India. The results of the 4th National Family Health Survey show that among children under five years old, 38.4% are stunted , 21% are wasted , 7.5 are severely wasted, and 35.7% are underweight . These numbers are closely linked with poverty: the percentage of underweight children decreases as the “wealth quintile” increases, from 49% among the lowest to 20% in the highest. Among adults, “deficiencies in the diet of both women and men are observed among those with little or no schooling, those in rural areas, those in poorer households, and those belonging to scheduled tribes and scheduled castes” . As these numbers suggest, many in India struggle with food insecurity, and this struggle is especially acute among marginal communities. My interviews with residents of a slum community in Bengaluru suggested that hunger was a daily reality. For these families, the rations provided by India’s Public Distribution System were not sufficient to cover their families’ dietary needs. They supplemented their rations in several ways—with food from their family members who remained farmers in their ancestral village, for example, or vegetables that were damaged and therefore cheaper—but they struggled to have enough to eat. This dissertation does not explore the lived realities of food insecurity among the urban and rural poor. This is not due to the declining significance of hunger, but rather because in India today, problems other than food insecurity motivate many interventions into the food system. Despite the continued challenges of hunger and malnutrition, the majority of my interlocutors— ranging from government officials to NGO leaders—who were involved in making and advising policy decisions were relatively unconcerned with food insecurity. This is at least in part due to my empirical focus on fruits and vegetables, which have not been part of India’s strategy for ensuring national food security.

Cell identity in the SAM is thus largely an issue of location rather than its developmental history

The astute student however, will note that this interpretation is not quite universal, as some researchers further postulate the existence of a fourth “Organizing Center” inserted between the CZ and RM tissues. Although not shown in Figure 2.0, the OC is equivalent to the rounded apex of L3, pushing the remaining part of the RM somewhat deeper into the stem. Until better genetic evidence is available though, only CZ, PZ, and RM will be used for the remainder of this dissertation. While the numbering system shown in Figure 12 does provide a useful set of spatial coordinates, it is also somewhat misleading as it implies that the SAM is static structure, unchanging over time. This could not be further from the truth. Instead, it must be remembered that the SAM is a site of plant growth, and as a result its cells are in a state of constant flux as they divide, grow, and differentiate. For example, the repeated perpendicular divisions that occur in L1 and L2 actually cause these layers to expand sideways, where the displaced cells eventually bend around the curve of the apical dome and become part of the cylindrical stem surface. The motion is reminiscent of the path taken by water droplets in an umbrella-shaped fountain, though the individual plant cells move considerably slower. If growth by lateral displacement is followed to its logical extremes, it is important to note that all of the founding cells will be pushed off to the sides over time, while new ones take their place in the middle. No single cell in the SAM is a permanent resident. The overall shape and size of an SAM is perhaps more analogous to a standing wave,growing pot where stability is the illusion caused by a dynamic equilibrium. Maintaining that wave is of course a difficult challenge, as the inputs to that equilibrium must be precisely matched to its outputs at all times.

Failure todo so would quickly rob the plant of its ability to grow, with obvious consequences for survival. Exactly how this balance is maintained is not fully understood, but the motion of the cells makes at least one part of the process perfectly clear: the cells must change their identity as they are moved from one place to another. Those that start in the CZ for example, switch to PZ gene expression patterns as they move further away from the middle, and may later adopt leaf and flower identities as they are incorporated into mature organs.The ability of a cell to determine its location within the SAM structure is thus of paramount importance, yet it must do so in the absence of any stationary reference point. So far as currently understood, each cell solves this problem in exactly the same way a person would do so: it talks to its neighbors. Based on what the individual cell sees and what its neighbors report seeing, it is possible to work out exactly where the cell is located in the overall plant structure. Of course in actual plant tissues such communication occurs largely through to the exchange of proteins, hormones, and RNA molecules, though increasingly evidence suggests that mechanical forces in the cell wall may also contribute some information [2]. Some molecules can travel further distances than others, some are modified en-route in order to become functional, and still others move from cell to cell in precise patterns, much like the knight in a game of chess. When these molecules are produced in different areas of the plant, the surrounding cells can estimate their relative locations to each other simply by reading the chemical bar-code in their local milieu, and then develop accordingly. At the present time, only a few such routes of chemical communication have been identified, two of which are plant hormones: auxin and cytokinin. Auxin is best known for increasing the volume of cells, though it also has roles in apical dominance and tropism growth patterns. Cytokinin meanwhile is known for stimulating cell division, in addition to other roles in senescence and pathogen responses.

Together the function of the two hormones would appear to complement each other very well in terms of overall growth, yet within the SAM they appear to mix about as well as oil and water. Cells that respond to auxin often don’t respond to cytokinin, and vice versa. Why this should be so is not well understood, but studies of root vasculature development suggest that their mutual exclusion is actually used to generate spontaneous patterns that help guide plant development. In callus tissue, the two hormones are often found to have response patterns arranged in a polka-dot like arrays, where each hormone “dot” is surrounded by a circular field belonging to the other. The SAM is organized around a single such dot, where cytokinin responses occur in the RM, and auxin responses occur in the PZ which often occur in discrete foci corresponding to new lateral organs. The CZ cells in contrast, do not appear to be sensitive to either hormone, but instead express both auxin and cytokinin biosynthesis genes . The production of cytokinin in the L1 and L2 is also consistent with the distribution of bioactive cytokinin concentrations observed with immunological techniques and with GFP reporter systems. This suggests a stable arrangement of three mutual exclusion zones within the SAM, which closely correspond to the known CZ, PZ, and RM tissues. Root apical meristems in contrast, appear to be based on the reciprocal arrangement, as roots have an auxin response dot in the middle surrounded by cytokinin responses in the overarching root cap, concentrated in the root cap columella cells.Another potential communication system that has been extensively studied involves a potential feedback loop between the CZ and RM cells, thought to be carried out by WUS and CLV3. WUS is a homeodomain transcription factor produced exclusively within the RM, but is capable of moving 2-5 cell diameters away from its center of origin.

WUS has also been shown to activate transcription of CLAVATA3 in the overlying CZ cells by directly binding to the CLV3 promoter. CLV3 in turn, is thought to be a small secreted oligopeptide that is modified with a few arabinose sugars. The mature glycoprotein then travels through the apoplast to reach leucine-rich receptor kinases in the RM, such as CLV1 or BARELY ANY MERISTEM1, thereby triggering a signaling cascade that ultimately suppresses WUS transcription. Many of the intermediate biochemical steps however, have not yet been fully identified, which makes it difficult to fully reject the feedback loop null hypothesis. There is also evidence of a more complex set of feedback loops, as WUS has been found to regulate components of the cytokinin signal transduction pathway , and exogenous cytokinin are able to stimulate WUS transcription. Altered cytokinin signalling pathways have also been shown to affect CLV3 expression patterns. WUSCHEL-LIKE HOMEOBOX5 , which is closely related to WUS, is known to participate in auxin pathways within the root, while the generation of SAMs from callus or root tissue has repeatedly been shown to require a pre-incubation on auxin rich media, where it may actually stimulate auxin transport . Micro RNA molecules may also be involved, as a variant of AUXIN RESPONSE FACTOR 10 that was resistant to miR160a was able to increase WUS and CLV3 expression patterns. Clearly, there is a lot going on. To help clarify how such cross-talk contributes to SAM structure, the research presented in this dissertation explores two closely related subjects. The first is the regulation of CLV3, which was studied by resolving the promoter structure of this gene in chapter 3. The results suggest that CLV3 is regulated in part by auxin responses,square pot while activation and/or repression is likely to be controlled complicated set of cis-motifs in the 3’ enhancer region. The presence of these 3’ motifs in a known transposon also suggests a novel origin of the WUS/CLV3 feedback loop. Chapter 4 meanwhile, explores the possibility that WUS and cytokinin responses form a second feedback loop necessary for SAM structure. This was done by narrowing down the possible cellular and biochemical routes by which cytokinin could affect WUS transcription, translation, and protein movement. The results however, suggest that the two pathways are atlargely independent of each other, though cytokinin responses may increase WUS stability in the RM. Unexpectedly, the data also found that the absence of cytokinin responses in the CZ is a critical part of SAM structure. The cytokinin response-free cells were also found to have an enhanced protein degradation mechanism, which may help shape the WUS protein gradient. Interestingly, WUS proteins were found to be rapidly degraded following auxin treatments, suggesting a model in which the SAM structure is defined by cytokinin-induced stability in the RM, and auxin-induced protein degradation in the surrounding CZ and PZ cells.The WUS-CLV3 feedback loop has long been an attractive model to explain how SAM structure is maintained in a dynamically changing cellular environment. Simply by combining activation of CLV3 with the repression of WUS, computer simulations have repeatedly shown that this is sufficient to maintain constant population of cells with CZ and RM identity. However, despite the simplicity of this model, the molecular mechanisms that carry out the feedback loop have instead revealed a number of potential complications. On the forward path for example, WUS is known to be a bi-functional transcription factor, activating and repressing several hundred different target genes.

Currently it is not currently known exactly how WUS switches from activator to repressor, but it has been shown to directly bind to DNA motifs in AGAMOUS and CLV3 regulatory regions, where it activates their transcription. Additional binding sites on repressed targets such as KANADI1, YABBY3, ASYMMETRIC LEAVES2 have also been identifie. Complicating this model of is the observation that CLV3 activation requires both WUS and SHOOTMERISTEMLESS in leaf tissues, suggesting that the presence of WUS alone is not sufficient. In addition WUS has also found to directly interact with the GRAS domain transcription factor HAMl, as well as the potent transcriptional repressor TOPLESS. TPL itself further has been shown to assemble a protein complex with Sin3 ASSOCIATED PROTEIN and HISTONE DEACETYLASE 19 [49, 50], suggesting a potential link between WUS and chromatin modification. In order to discriminate between the two models, this study began by attempting to identify the cis-regulatory environment around the CLV3 locus. The CLV3 expression pattern was firstcarefully recorded with a GFP reporter, which in contrast to previously published RNA in-situ’s, found layer-specific differences in CLV3 transcriptional output. The regulatory regions of CLV3 were then annotated by mapping predicted transcription factor binding sites and computationally significant cis-motifs, which were further resolved with phylogenetic footprinting. This analysis found that CLV3 has a very simple 5’ promoter, containing an auxin responsive element, suggestive of ubiquitous expression. The 3’ enhancer in contrast, contained at least 3 large cis-regulatory modules, two of which were found within a naturally occurring transposon, while the 3rd included several known WUS binding sites. On the basis of promoter deletion experiments, all three cis-regulatory modules were found to be required for CLV3 activation. The existence of the transposon in turn, has several implications for the evolution of the WUS-CLV3 feedback loop and Brassicaceae plant anatomy. Previous reports of the CLV3 expression pattern have consistently found it localized to the apex of the SAM, where it is often used as an indicator of CZ cell identity. Within this region, the expression pattern is somewhat variable, as previous RNA in-situ revealed a narrow inverted cone-shape, while GFP and GUS reporters often produce more indistinct rounded shape 3-4 cell layers deep. In contrast, the present study found a slightly more complex pattern when viewed as a longitudinal section. In perfectly centered sections, the pCLV3:mGFP5-ER reporter often appears in an inverted cone shape, but the expression zone is noticeably broader than the previous RNA in-situ results . As the section plane is displaced from the central axis and becomes more tangential, a conspicuous gap is frequently visible, where the L2 cells have less fluorescence than those immediately above and below. This suggests a bi-partite expression pattern where a flat, circular domain occurs specifically in the L1, and a second spherical domain occurs underneath in the L3 cells . In order to identify the CLV3 regulatory structure, this work began by annotating all known regulatory motifs on an 8kb genomic sequence centered on At2g27250.

Suppose that the polygyny threshold in equation were satisfied by an equality

In order to produce analytically tractable results, we simplify by assuming throughout that there are only two types of males, rich and poor, with rich males being a fraction u of the population. All rich are identical, as are all poor. The rich males are indexed by r and the poor by p. We now demonstrate two theoretical results with the potential to resolve the polygyny paradox. First, diminishing returns to additional wives arising from causes other than necessity to share a husband’s rival material wealth will reduce the number of wives acquired by each rich male. Second, because of this fact, a highly unequal wealth distribution with few extraordinarily rich men may produce little polygyny, while a less unequal wealth distribution with a larger fraction of rich men may produce a greater extent of polygyny. Two rich men, for example, can be expected to have more wives in total than one very rich man whose wealth equals their combined wealth. For this same reason, the Gini coefficient—see table 2 for a definition—is not a sufficient statistic for the analysis of the relationship between polygyny and wealth inequality. We take up each of these results, in turn, before assessing if our empirical estimates are consistent with this explanation.If we assume that male demand is limiting, then equation determines the number of wives each rich man will have. It is clear from inspection of equation that a greater extent of diminishing fitness returns to additional wives produces a lower male demand for additional wives. This is demonstrated mathematically in the electronic supplementary material. Determining the effect of greater diminishing returns to additional wives when female supply is limiting is more challenging. As noted above, if female supply is limiting,1 litre square plant pots the value of n* implied by the polygyny threshold inequality in equation has no closed form solution.

To address this challenge, we proceed as follows.Then a reduction in d, holding all other terms constant, would reduce the right-hand side of the equation—the fitness of each of the n wives of a rich man—while having no effect on the left-hand side—the fitness of a singleton wife. Thus, holding all else equal, an offsetting decrease in n would be required to restore the equality. This is demonstrated in the electronic supplementary material by differentiating equation with respect to d. This means that a man who was just barely rich enough so that an unpaired woman would choose to marry him as wife number under the initial d, would, under the lower d, be unable to secure the unpaired woman’s partnership. As such, an increase in the extent of diminishing returns to additional wives will reduce both male demand for, and female supply to, polygynous marriage. Our results imply that if d , 1, a larger quantity of moderately rich men can be expected to have more wives in total than a smaller quantity of even richer men, holding constant the total wealth held by the rich across these cases. This first finding will interact with our second finding, discussed below, concerning the effects of the population density of the rich class of men on the frequency of polygyny and the level of wealth inequality. In the electronic supplementary material, we present an alternative approach to account for diminishing marginal returns to increasing number of wives and find that our insights do not depend on the specific way in which diminishing fitness returns to increasing number of wives are modelled.To address prediction P1, we present empirical estimates of m and d . These values are estimated using a multi-level regression model fit to our individual level data; methodological details are provided in the electronic supplementary material. In all but four of the populations in our sample, the estimated d coefficient is reliably less than 1. This result provides cross-cultural empirical support for the first of the two conditions needed to generate a transition to a greater degree of monogamy with increasing wealth inequality.

Note two further results also shown in figure 5. First, our estimates for m are quite low, particularly across the agricultural economies. Second, our estimates of d 2 m are positive in almost all populations, including those that are concurrently polygynous and those that are serially monogamous. The consistently small values of m across all of our samples, even the monogamous ones, was unexpected. However, these low values reflect changes in male fitness per wife. Because of biological limits to the rate of reproduction in human females, significant increases to wealth are constrained to have less than proportional effects on fitness per wife. The effects observed here are more likely to reflect the ability of males with more than a threshold level of resources per wife to minimize offspring mortality, rather than to significantly enhance their own fertility. Though not discussed in detail here, our data suggest that male wealth impacts male fitness primarily by increasing the rate of wife acquisition rather than by increasing reproductive success per wife . Our second point addresses the possible concern that our estimates of d may be low, in part, because we use times married as our measure of polygyny. While it is true that men can accumulate a greater maximal number of marriage years through concurrent polygyny than serial monogamy, figure 5a demonstrates that the use of times married is an appropriate measure of polygyny for our purposes. Across almost all populations, the elasticity of fitness with respect to times married, d 2 m, is positive and reliably non-zero. Because these estimates measure the population-specific effects of cumulative number of wives on reproductive success, they demonstrate that an increased number of marriages leads to increased reproductive success in both types of marriage systems—concurrently polygynous and serially monogamous.We have established that there exists a strong cross-cultural pattern of decreasing—but reliably non-zero—fitness returns to increasing number of wives for reasons beyond rival wealth sharing.

We now turn our attention to testing if the transition to agriculture is associated with a decreasing fraction of wealthy males. In our theoretical model, we assume a discrete two-class wealth distribution, but empirical wealth data typically have continuous distributions. To deal with this issue, we consider two proxy measures for per cent rich in our empirical data: the minimum percentage of men that account for a fraction f of the total wealth and the frequency of men with more than c wealth, where c is the empirical midpoint in each population between the average wealth of males with one wife and the average wealth of males with two wives. More details about these metrics are included in the electronic supplementary material. Table 3 provides population-level posterior estimates of the completed wealth and completed polygyny measures, with the mean estimates by subsistence type shown in the bottom panel. To address prediction P2, we calculate empirical estimates of the fraction of rich men by production system . We find that agricultural populations have a significantly reduced frequency of wealthy individuals relative to horticultural populations. All four panels show reliable differences in mean per cent rich between the horticultural and agricultural subsistence modes. This lesser fraction of wealthy individuals suggests a decreased number of men both able and willing to take second wives. This in turn leads to reduced levels of per cent female polygyny in contexts where large wealth differentials are not able to underwrite large differentials in wives due to the existence of diminishing fitness returns to such additional wives. A limitation of this last result is that it is based on data from only four agricultural populations, three of them concentrated in a restricted region and time period . Moreover, a more informative dataset would come not from agricultural populations in the time period between the 1700s and 2000s, but rather from the agricultural populations in which monogamy actually began to emerge denovo. In our main analysis, we use estimates derived from the individual-level records available in the populations shown in table 1; in the electronic supplementary material,macetas por mayor we present comparable analyses that include 14 additional wealth distributions from historical agricultural populations. The results of this supplementary analysis are consistent with our arguments here—and in fact show stronger and more reliable effects in the direction predicted by P2. These supplementary data, however, are based on sometimes contested reconstructions of the historical wealth distributions pieced together by archaeologists and economic historians;they must be appreciated within the constraints associated with such forms of data.Using individual-level data from 29 populations, we show evidence of a general cross-cultural pattern of decreasing marginal fitness returns to increasing number of marriages. Further, using these same 29 datasets , we demonstrate the existence of an increasingly skewed distribution of material wealth in class-based agricultural societies . Both of these empirical findings are consistent with our model-based explanation for the decline of polygyny in societies engaged in agricultural production.We use cross-cultural data and a new mutual mate choice model to propose a resolution to the polygyny paradox. Following Oh et al., we extend the standard polygyny threshold model to a mutual mate choice model that accounts for both female supply to, and male demand for, polygynous matchings, in the light of the importance of, and inequality in, rival and non-rival forms of wealth.

The empirical results presented in figures 5 and 6 demonstrate two phenomena that are jointly sufficient to generate a transition to more frequent monogamy among populations with a co-occurring transition to a more unequal, highly stratified, class-based social structure. In such populations, fewer men can cross the wealth threshold required to obtain a second wife, and those who do may be fabulously wealthy, but—because of diminishing marginal fitness returns to increasing number of marriages—do not acquire wives in full proportion to their capacity to support them with rival wealth. Together, these effects reduce the population-level fraction of wives in polygynous marriages. Our model demonstrates that a low population-level frequency of polygyny will be an equilibrium outcome among fitness maximizing males and females in a society characterized by a large class of wealth-poor peasants and a small class of exceptionally wealthy elite. Our mutual mate choice model thus provides an empirically plausible resolution to the polygyny paradox and the transition to monogamy which co-occurred with the rise of highly unequal agricultural populations. We, however, cannot yet explain the causes of the unexpectedly substantial decreasing marginal fitness returns to increasing number of marriages. A purely statistical explanation of our results could be that we have missed some important rival form of wealth, which if accounted for would result in a larger estimate for m and hence a reduced estimate of the degree of diminishing returns to additional wives for reasons other than the sharing of rival wealth. Another possibility, already mentioned, is that in some of our datasets the very wealthy could be deliberately limiting their reproductive success , which would also drive m downwards. In addition to these possible statistical effects, there are a number of other plausible causes of the diminishing returns to additional wives observed in our populations. One possibility is that a male’s time and attention are rival inputs to his own fitness. This situation is likely to arise when paternal investment is essential to offspring survival and well-being. A male’s time can also be rival in other fitness relevant ways. For example, it may be difficult for a single wealthy man to effectively mate guard a large number of wives. With a wealth ratio of mr ¼ 2 and a per cent rich of u ¼ 0.5, a single rich man will have to monopolize his two wives in the face of challenges from a single unmarried man on average; however, with a wealth ratio of mr ¼ 10 and a per cent rich of u ¼ 0.1, a single rich man will have to defend his 10 wives from nine unmarried men on average. As the wealth ratio grows even more skewed, this situation could become increasingly difficult to manage . A related possibility is that a growing number of unmarried men could socially censure wealthy polygynous males, imposing costs on them that reduce male demand for and/or female supply to polygynous marriage. A third possibility is that sexually transmitted infection burden could diminish returns to polygyny, if polygyny enhances infection rates.

All cultivated citrus species or citrus relatives are susceptible to the disease

The model also predicted that limited areas in California are climatically favorable for HLB establishment, but the probability of establishment was predicted to be much lower compared to Florida. To increase the confidence regarding the model projection, a Principle Component Analysis was performed to investigate the climate similarity of regions with proven HLB presence with the California climate. PCA analysis showed that the climate in areas around Los Angeles overlapped with the climate of regions where HLB is currently present. On a global scale, HLB predictions from MaxEnt combined with expert knowledge could be informative for countries such as Australia, New Zealand, and European countries, where HLB has not been reported thus far. Oxytetracycline has been used extensively for over 60 years in agriculture for both plants and in animal health. The tetracyclines as a chemically diverse family of compounds have multiple activities across many organisms. Within this large family of compounds, a select subgroup has discreet and potent activity against α-proteobacteria, including CLas, while demonstrating inactivity against human bacterial pathogens labeling them as “non-antibiotic tetracyclines” a designation accepted by the FDA. Our efforts in tetracycline semi-synthesis have produced three separate series of compounds found effective against the surrogate strain Liberibacter crescens and with increased potency, while in a study of over 35 derivatives distinct structure-versus-activity parameters have emerged guiding the further design and synthesis of compounds active against Liberibacter species. One series of positional derivatives was three orders of magnitude more active than oxytetracycline,macetero de 7 litros while the others were at least two orders of magnitude more active in this surrogate strain.

The most potent compounds derived from the screening were examined in further studies of trans-bark uptake in young citrus trees, showing that proper formulation demonstrated transport throughout the plant and into the canopy. Further studies in HLB-infected citrus trees by bark or foliar application decreased PCRbased bacterial levels after one month of treatment while shoots collected from HLB-infected Valencia orange shoots showed significant repression of L10 and 16S mRNA levels. These preliminary results demonstrate that chemically-modified tetracycline derivatives are active specifically against HLB, lowering infection burden in whole plants, and are considerably more active than oxytetracycline. The case for novel and inexpensive compounds specifically designed for citrus plants harboring α-proteobacteria infections will be presented along with its potential to replace oxytetracycline for agricultural use. Besides the availability of financial and technological resources, and citrus growers’ awareness about the damages that mismanagement of the Huanglongbing can cause to their and neighbors’ groves, the decision of applying the Asian citrus psyllid control and symptomatic trees eradication by citrus growers depends on an economic analysis of the benefits and costs of any measure adoption in the short , medium , and long-term . Although basic information about the temporal progress of HLB and damage in plants of different age, scion/rootstock combination, and under different HLB management still scarce, a macro of Excel was developed to estimate and quantify the future impact of HLB in groves adopting different kinds of disease management. In this study, that macro was adapted to simulate the impact on production of citrus groves under different scenarios of HLB management , grove ages at the beginning of the epidemic , and initial incidences of HLB-symptomatic trees .

Considering that the assumptions and models were corrected, for high expected yield of healthy groves and moderate annual rate of HLB incidence in scenarios with ACP control , it can be concluded that groves younger than 6 years old at the time of HLB detection will have higher expected productivity in any term and initial disease incidence only if managed with eradication and reset of symptomatic plants and ACP control. Older groves with lower initial disease incidence may have a medium-term productive survival , only controlling ACP enough to not allow the secondary spread of the disease. However, the impact on fruit quality of symptomatic trees kept in the field was not considered in this study. The Asian citrus psyllid, Diaphorina citri Kuwayama, transmits Candidatus Liberibacter asiaticus, causal agent of the deadly bacterial disease called Huanglongbing or citrus greening. D. citri and Ca. L. asiaticus are well established in Florida, and have been reported from other states including Louisiana, Texas, and California; they pose a real threat to the entire US citrus industry. In order to discover known and unknown D. citri viruses which might be useful for virus-based biological control strategies, we constructed small RNA cDNA and RNA-seq libraries and used next generation Illumina-based sequencing for selected, worldwide D. citri populations from Taiwan, China, Brazil, and the US Through deep sequencing analysis and de novo contig assembly, larger contigs were obtained. BLASTX and tBLASTx searches against the viral database available in GenBank suggested distinct viruses shared protein sequence similarity with Reoviruses, and with Picorna-like viruses from the genus Iflavirus. Subsequent RT-PCR and Sanger sequencing confirmed the presence of these viruses in some but not all populations of D. citri investigated in this study. Here, we are reporting the first Picorna-like virus discovered in D. citri. However, our analysis suggested that, although encoded proteins show low but significant similarity to viruses belonging to the genus Iflavirus, the D. citri virus is not an Iflavirus and appears to be representatives of a new genus.

We were able to build 70% of the genome of this new virus through bioinformatics analysis. The genome sequences were completed by filling up the gaps using RT-PCRs and specific designed primers. Both 5` and 3` UTR full-sequences were obtained using RACE strategies. Our intent is to engineer this virus and assess its effects on D. citri. Sustainable long-term measures to combat HLB via breeding or genetic engineering methods are hampered by the fact that no true genetic resistance has been found in citrus germplasm.However, the degree of HLB susceptibility or tolerance varies among citrus species. There have been suggestions toward the identification of innate ‘Ca. Liberibacter asiaticus’ resistance-associated molecular mechanisms in citrus plants for application in breeding or genetic engineering crop development programs. Furthermore, a recent study showed that a continuous heat treatment of 40°C to 42°C for a minimum of 48 hours was sufficient to significantly reduce Las titer or eliminate Las entirely in HLB-affected citrus seedlings. Plant exposure to one form of stress has been shown to serendipitously induce resistance to other forms of stress. In this study, we conducted proteomics analysis of heat-treated HLB-affected lemon plants, detected proteins that were markedly up-regulated only in plants that were simultaneously exposed to heat and Las. This suggests that heat treatment induces proteins in Las-infected citrus plants that could play an active role in the suppression of Las growth. Hence, this research demonstrates that: the application of a proteomics approach to elucidate the molecular mechanisms involved in heat-induced Las-resistance in citrus plants and the use of the information from proteomics analysis to develop genetically-modified Las-resistant citrus plants by altering host gene expression to mimic heat-induced conditions. A nationwide survey was conducted to come up with a comprehensive data on the extent of HLB incidence and strains, and its insect vector on Philippine citrus. A total of 120 citrus farms in the various citrus growing areas in the country were surveyed. Typical symptoms of HLB were found in varying degrees of severity in 57% of the farms surveyed. The typical HLB symptoms assessed include sectoral yellowing, mottling,macetas 30 litros small leaves with zinc deficiency symptoms, interveinal chlorosis, vein corking, lopsided fruit, inverted fruit coloration, and aborted seeds. Disease samples were collected and confirmed through starch Iodine test and Polymerase Chain Reaction . There was a good agreement between the visual assessment of symptoms and identification by iodine starch test and PCR. Besides HLB, the occurrence of Asian Citrus Psylla was also noted through visual search and stem tap technique. ACP was noted in 12% of the farms surveyed. In some farms, however, no ACP was found although HLB symptoms were observed and disease spread is evident due to the presence of newly infected trees within the orchards. Disease samples were also graft-inoculated onto differential hosts to determine the HLB strains present in Philippine citrus. Based on disease index on differential hosts, Strain I and II are the predominant strains of citrus HLB found in the Philippines.The Asian citrus psyllid is responsible for transmitting greening or Huanglongbing to citrus. It is considered the most debilitating disease of citrus worldwide. Currently, citrus growers rely on insecticides to control ACP. ACP is a dominantly visual insect and, as such, it is important to understand its visual behavior. Previous studies have shown that young trees planted on a bed covered with metalized polyethylene mulch reduced ACP populations and, consequently, incidence of HLB. However, the actual mechanism whereby the metalized mulch protects trees from ACP is not known. One hypothesis is that radiation of ultraviolet light from the ground confuses the approaching psyllid and disrupts flight. To test this hypothesis, we developed laboratory experiments to evaluate ACP response to UV light. We tested both light emitting diodes and monochromatic colored visual targets produced with narrow band pass filters. ACP were attracted to UV more strongly than to blue and red, but less strongly to yellow and green. UV LEDs emitting a wavelength of 375 nm were found to be the most attractive to ACP amongst a range of UV LEDs . There was no difference between male and female ACP in terms of their attraction towards UV. We hypothesize that metalized mulch, which reflects UV, could be disorienting to the ACP as UV light is in nature primarily found in the sky.

These studies improve our understanding of ACP visual behavior and provide the basis for future studies.Early warning surveillance is crucial in areas that are not yet infected with Las or that have been newly planted with healthy trees. The success of HLB control in these areas relies on the detection of disease and instigation of mitigation procedures as early as possible in the epidemic. Control measures that are instigated too late may not be effective and will incur far greater control costs and disease-induced yield losses than epidemics that are caught early. Surveying and scouting is however expensive and surveillance programs necessarily cover large geographic areas, stretching fiscal and manpower resources. Understanding how to target resources across vast spatial areas is not trivial given the complex spatial distribution of plantings, vector dispersal patterns, interactions between residential and commercial citrus areas and unknown points of disease entry. Using state-of-the-art epidemic simulation methods coupled with geographic information systems , we incorporate this information and use it to simulate realistic spread patterns. By combining the epidemic models with stochastic optimisation algorithms, we are able to identify optimal ‘smart-surveillance’ programs that maximize the probability to achieve early warning based on the predictions of spread. We identify a number of general rule-of-thumbs to help inform optimal surveillance design. In particular, we illustrate that the optimal spatial distribution of sampling resources at the landscape scale depends on the sensitivity and specificity of sampling at the scale of individual trees and plantations . Thus, as new sampling, diagnostic, and detection technologies become available, the methods we are developing can help identify deployment strategies that get the most out of available technologies. The method can be tailored to specific areas and regions, each of which have unique environments and face different situations in terms of, for example, vector densities and inoculum pressures. Psyllid host searching behavior is complex and sophisticated. It can be influenced by host species, growth stage, and physiological condition, psyllid gender and mating status, behavioral plasticity, usurpation by phytopathogens of host aromas, and psyllid-induced emission of foliar volatiles. ACP relies on visual cues to locate its host plants, but evidence suggests that olfactory cues mediate visual response. Scent lures could potentially enhance psyllid response to the bright yellow and green background colors of the sticky traps used in ACP monitoring programs. However, because host foliage aromas are complex, dynamic, and species-specific, developing an effective scent lure is challenging. Here we explore some aspects of lure composition and deployment which may increase trap yield: Scent lure efficacy may be influenced by setting. In residential areas, a generalized scent lure comprised of volatiles common to several host species may work well, while a scent lure used in groves might need to mimic the scent of the grove trees to be effective. Alternatively, a lure that mimics ‘super hosts’, such as orange jasmine, may work well in a variety of situations.

Of the fruits evaluated the fewest isolates were obtained from grapes

Given that both methods capture genetic relatedness among accessions, a significant relationship between these two methods is expected.Principal component analysis revealed significant population structure defined by geography and use, but strong signals of genetic structure also exist at the level of pedigree relatedness. Previous work determined that 75% of the accessions evaluated here are related to at least one other accession by a first-degree relationship, and over half of the accessions are interrelated and form a single, complex pedigree network.Both the strong population-level and pedigree-level signals of genetic structure in our sample present challenges in genetic mapping as these are significant confounding factors when performing GWAS. Moreover, the rapid LD decay previously described for this and other diverse populations of V. vinifera suggests that millions of SNPs are required for well-powered GWAS in grapes.Despite our relatively low marker density and the challenges presented by strong genetic structure, we performed GWAS for all 33 phenotypes. For most traits, we found no convincing GWAS signals . However, we reasoned that we may find SNPs associated with key traits that experienced strong selection during domestication and breeding because selection results in extended LD surrounding the targeted loci, thereby requiring a lower SNP density than that required to map-unselected traits. We hypothesized that, by combining association mapping with selective sweep mapping ,macetas con drenaje we may identify loci associated with traits targeted during grape domestication and breeding. A key transition in grapevine domestication was the switch from dioecy to hermaphroditism: all wild Vitis species, including the ancestor of V. vinifera, are dioecious, and nearly all V. vinifera are hermaphroditic.

Hermaphroditism was likely the first, and arguably the most important, transition from wild vines to cultivated grapes: it enables self-pollination and subsequent clonal propagation of elite cultivars without the need for pollinators.Dioecy is found at low frequency in our sample: only 50 of the 550 accessions with flower sex data were labeled as dioecious. Despite this low frequency, we identified SNPs significantly associated with flower sex on chromosome 2 . The most significantly associated SNP overlaps with the 1.5 Mb region repeatedly identified via linkage mapping.This SNP is also found within the fine-mapped 143 kb region believed to harbor the causal flower sex locus.We therefore demonstrate that, even with only 50 accessions carrying the ancestral dioecy phenotype, we successfully map the flower sex locus at relatively high resolution using GWAS relative to traditional linkage mapping approaches. A genome-wide Fst scan comparing dioecious to hermaphroditic accessions also revealed that the SNP most strongly associated with flower sex had the highest Fst value genomewide, consistent with the effect of selection for hermaphroditism at this locus . If grape domestication resulted in a rapid increase in the frequency of the hermaphroditism allele, one would expect extended haplotype homozygosity, and thus extremely high xpEHH values, in and around the flower sex locus. While none of the xpEHH values at the flower sex locus fall within the top 1% most extreme values genome-wide, we do observe a suggestive peak with xpEHH values within the top 2.6% of genome-wide xpEHH values . xpEHH values in the bottom 1% of the genome-wide distribution are found directly adjacent to the flower sex locus identified here. We have no explanation for why a potential signature of selection could exist for dioecy in such close proximity to the flower sex locus. There are SNPs with extreme xpEHH and Fst values, indicating potential selection for hermaphroditism, at the distal end of chromosome 1 ranging from positions 366 to 467 kb . This genomic region overlaps with the region previously associated with flower sex in a bi-parental mapping population using the same Vitis9KSNP microarray employed for this study.

However, thisregion is several Mb from the locus highlighted in Figure 6a that color within a diffuse peak on chromosome 2 between 10 and has been repeatedly associated with flower sex. We hypothesize 17 Mb . Although the genomic region containing that this distal signal of selection is due to inaccurate localization significant GWAS hits for color overlaps the VvmybA1 gene, the of the array’s SNPs in the reference genome since, when this trait most significantly associated SNP found here is 3.6 Mb from the is mapped using genotyping-by-sequencing in the same bi- known causal mutation. Our inability to map the known color parental population, the flower sex colocalizes with the known locus with precision is consistent with results from rice and flower sex locus according to the reference genome.It is unclear Arabidopsis where markers with the strongest association why such mismapping occurs with the Vitis9KSNP array data, but signals were not found directly at known causative loci. Moreover, unexpected hybridization of non-targeted paralogous regions this result is unsurprising given the relatively low marker density may possibly contribute to these observations. of the SNP array employed here. Skin color in grapes is largely controlled by a single locus on While the diffuse association signal for grape color spanning chromosome 2, where a retrotransposon insertion in the MYBA1 nearly 7 Mb indicates that we have poor mapping resolution for gene results in a loss in pigmentation by disrupting anthocyanin this phenotype, it also suggests the presence of long-range LD biosynthesis.Although rare, white-skinned grapes have been potentially caused by selection. Saccharomyces cerevisiae is an important experimental model organism in addition to its commercial significance as the predominant yeast species during wine fermentation. Modern strains of S. cerevisiae are thought to have arisen in Asia given the diversity of strains and reproductive isolation observed in a study of S. cerevisiae isolates from human-associated and non-human-associated environments in China .

Distinct linages were observed for isolates from primeval and secondary forests . However this study considered few isolates from wine environments and found fewer isolates of S. cerevisiae from fruit sources and more from tree bark, rotting wood and soil samples than from fruit samples. The authors concluded that grape and orchard isolates were similar to those of the wine European lineage. Our goal was to evaluate in greater depth the diversity of natural vineyard isolates from two wine regions in China. Several studies have reported on the genetic diversity of S. cerevisiae strains in different wine-producing regions. These studies revealed that geographic region , climatic conditions , vintage , grape varieties and must characteristics , inoculation of starter yeasts , and SO2 addition affected the diversity of S. cerevisiae observed. In many cases genetically distinct strains of S. cerevisiae were isolated from the same fermentation during wine fermentation . The diversity of S. cerevisiae strains present in fermentations has been shown to play an important role in the characteristics of the final product . Numerous molecular methods have been developed to study the ecology and population dynamics of S. cerevisiae strains . Interdelta sequencing typing uses the variation of the number and position of the delta element, a repeated sequence that flanks the Ty1/Ty2 retrotransposon , that allows interpreting strain similarities and evolutionary or adaptive distance . A succession of different S. cerevisiae strains are established during native as well as inoculated fermentations that could have positive or negative effects on the course of fermentation and wine quality . Vezinhet et al. analyzed the evolution of S. cerevisiae strains isolated from spontaneous fermentations during six consecutive years. These authors concluded that the wide distribution of some strains in the studied areas and their presence over years,macetas 7 litros constitute evidence for the occurrence of specific indigenous strains representative of an enological region. China is an important wine-producing country and while some studies have investigated indigenous yeast species and population dynamics during wine fermentation within local viticulture regions ; few studies have focused on the breadth of the diversity of S. cerevisiae wine genetic resources of China. A study of human- and non-human-associated strains of China found novel distinct lineages only distantly related to the wine strain linages . The genetic diversity and relatedness of indigenous wine S. cerevisiae resources have not been extensively compared with that of wine strains isolated from other geographic regions. Ningxia and Xinjiang provinces, where the strains in this study were isolated, are two of the oldest wine producing regions in China. Shanshan, Xinjiang in northwestern China belongs to a temperate continental climate, with an average temperature of 12˚C. It is situated 92°22′E, 42°87′N with an average altitude of 3986 m.

Qing Tongxia, Ningxia in north central China also belongs to a temperate zone with an arid and semi-arid climate. It is situated 105°21′ to 105°21′ E, 37°36′ to 38°15′N with an average altitude of 1118 m. A comparison of the genetic diversity of S. cerevisiae resources in different viticulture regions of China with isolates from other diverse geographical regions is of importance to the study of global S. cerevisiae ecology. In the present study, interdelta sequence typing with improved primers was used as genetic marker for the distinction of S. cerevisiae strains. Dendrograms were constructed based on similarity among different patterns of bands and the genetic relationships of all strains were evaluated. The strains used in the study were either isolated from fermentations of different grape varieties in the Ningxia and Xinjiang Provinces in China or obtained from the Department of Viticulture and Enology Culture Collection at the University of California, Davis. The aims of the present work were to evaluate the genetic diversity and relatedness amongSaccharomyces strains of different geographic origin, to establish a strain collection to preserve the S. cerevisiae genetic resources of China, and to identify strains useful for further development for commercial wine production in China. Fifty-four isolates collected from fifteen spontaneous fermentations of grapes grown in China and one commonly used commercial yeast, Lavin RC212, were used in this study and obtained from the collections of the College of Enology, Northwest A&F University, Yangling, Shaanxi, China. This set of strains was selected on the basis of interdelta sequence profiles from a total of 349 isolates collected from fifteen spontaneous fermentations of grapes grown in Shanshan, Xinjiang and Qing Tongxia, Ningxia. Fifty-nine yeast colonies were isolated from six spontaneous fermentations of different commonly used grape varieties: Red Globe, Small-berry Thompson Seedless, Big-berry Thompson Seedless, Merlot, Mixed red and Mixed white in Xinjiang. Two hundred ninety isolates were obtained from nine spontaneous fermentations of the grape varieties Cabernet Gernischt, Cabernet Sauvignon, Cinsault, Merlot, Pinot Noir, Riesling, Sauvignon Blanc, Semillon, and Yan73 in Ningxia . The grape must fermentations were allowed to proceed spontaneously at 25~28˚C for 7~11 days until dry. Fermentations were sampled at early, mid and the final stage of fermentation, and serial ten-fold dilutions were inoculated onto WLN and incubated for five days at 28˚C.These yeasts were differentiated and classified according to colony morphology and color. S. cerevisiae isolates were purified and then maintained in 20% glycerol at -80 °C until further analysis, resulting in the selected set of 349 isolates for the interdelta sequence analysis. The composition of the different grape musts is reported in Supplemental Table 1 for Ningxia and in Supplemental Table 2 for the fermentations from Xinjiang. The fifty-four yeast strains selected from this larger population of isolates represented the major strain clusters of interdelta sequence profiles identified in the earlier preliminary study. The origins of the 54 isolates used in this study are shown in Table 1. Identification of S. cerevisiae was confirmed by PCR-RFLP of the 5.8S-ITS rDNA using restriction enzymes HaeIII, HpaII, and ScrFI as described by Li et al. . Strains were maintained in frozen stocks at -80˚C before use. Note that a similar strain numbering system was independently used by Wang et al. in their study but the strains are unrelated. We retained our numbering system since that is the designation given to the strains in the Northwest A&F University strain collection. Other strains were obtained from the Wine Yeast and Bacteria Collection of the Department of Viticulture and Enology at the University of California, Davis. The data from all fifty-two Saccharomyces isolates listed in Table 1 of Liu et al. were included in this study as the method of interdelta sequence analysis was identical. These yeast strains were collected from California, France, Italy, Northern Europe, and Spain .The interdelta sequence patterns obtained after gel electrophoresis were used for the construction of a presence/absence matrix, taking into account the total number of different bands observed. The interdelta sequence patterns were obtained following electrophoresis.

The extent of shocks will also differ across wealth classes and economic systems

The key thesis to be explored is that for some kinds of wealth and some economic systems the parents’ wealth strongly predicts the wealth of the offspring. In particular, the cattle, land and other types of material wealth of pastoral and agricultural economies are directly transmitted by simple transfers, often buttressed by social conventions of inheritance. By contrast the somatic wealth and skills and the social network ties central to foraging and horticultural livelihoods are more subject to the vagaries of learning, genetic recombination, and childhood development. Moreover, in foraging and horticultural economies, such material wealth as exists tends to circulate through broad social networks rather than being vertically transmitted to offspring. A corollary of the thesis is that, if our model is correct, economies in which material wealth is important will show substantial levels of wealth inequality. Both the thesis and the corollary find strong support in our data. We focus on small-scale societies because they offer the greatest variation in both the technologies by which a livelihood is gained and the basic institutions that provide the incentives and constraints regulating economic life, including the dynamics of inequality and the inheritance process. . These societies thus provide the most powerful lens for exploring hypotheses concerning the importance of technologies and institutions in explaining the dynamics of inequality and, thus, may also illuminate long-term trends in contemporary and future economies. The connection between wealth inheritance and wealth inequality is the following: If wealth is strongly transmitted across generations, chance shocks to the economic fortunes of a household due to disease or accident,frambueso maceta luck in a hunt or harvest, and other environmental disturbances or windfalls will be reproduced in the next generation.

These effects will thus accumulate over time and thereby counteract the widely observed inequality dampening tendency of regression to the mean . We seek to understand the effects of this process by examining how the offsetting effects of random shocks and imperfect transmission across generations jointly determine a steady state distribution of wealth for differing kinds of wealth and across the four different economic systems . The institutions and norms that characterize distinct economic systems and the nature of the wealth class alike will affect the degree of inter generational transmission.For a number of modern economies, there are quantitative estimates and comparisons of the inter generational transmission of education, occupational prestige, nonhuman physical capital, and other forms of embodied and material wealth . For small-scale populations, associations between reproductive success and material forms of wealth have been studied , and there exist piecemeal estimates of inter generational transmission of, for example, fertility and height . But there are no estimates allowing a comparison across populations of the inheritance of the distinctive kinds of wealth that are central to the livelihoods of small-scale communities of foragers, horticulturalists, herders, and farmers. Here we present a new set of data and conduct a quantitative comparative analysis of the transmission of distinct types of wealth among the 21 populations shown in Fig.1 and Table 1. Further information is provided in .Since the development of human capital theory a half-century ago, it has been conventional to treat wealth as a multidimensional attribute, as evidenced by the adjectives now routinely applied to the word “capital,” namely, social, somatic, material, cultural, and network . We identified three broad classes of wealth in our populations, namely, embodied; material ; and relational . We have no measures of other heritable determinants of well-being such as ritual knowledge, an important source of institutionalized inequality in some populations.

By linking the level of wealth of parents and adult offspring, measured as appropriate for individuals or households , we are able to estimate the degree of inter generational persistence for particular types of wealth and then to create averages for each broad class of wealth. We classify economic systems according to the conventions of anthropology . Hunter gatherer economic systems are those that make minimal use of domesticated species , whereas pastoralists rely heavily, though rarely exclusively, on livestock kept for subsistence and sometimes commercial purposes. Although both horticulturalists and agriculturalists use domesticated plants and animals, horticulturalists do not typically use ploughs, their cultivation is labor- not land-limited, and land markets are absent or limited. As with all classificatory systems, there are some ambiguities of assignment of our populations to these classes, but the least improbable reclassifications do not affect our results [see , section 4]. Transmission of wealth across generations need not take the form of bequests, or the literal passing on of physical objects . What matters for the long-run dynamics of inequality is anything that results in a statistical association between the wealth of parents and children. This statistical association may be enhanced by positive assortment in mating or in economic pursuits as occurs when skilled hunters pursue prey together, or when successful herders cooperate in livestock management. The same is true of increasing returns or other forms of positive feed backs, for example when those who invest a substantial amount earn higher than average returns, or when childhood developmental effects associated with modest genotypic differences result in substantial phenotypic differences. Negative feed backs, such as sharing norms that extract substantial transfers from the wealthy, or wealth shocks that are inversely correlated with one’s wealth , by contrast, heighten regression to the mean by reducing b, thereby attenuating the persistence of inequality over time and hence reducing steady-state inequality.

Our three wealth classes differ in the extent to which these transmission mechanisms—transfers, assortment, and positive feed backs in development or accumulation—are at work. Material wealth is readily transferred to the next generation by bequests sanctioned by cultural rules. Moreover, because it is typically observable, material wealth can facilitate deliberate marital or economic assortment. For some types of material wealth , the correlation of material wealth levels across generations is further enhanced by the presence of increasing returns to scale or other positive feed backs. Network ties can easily be passed from parent to child, but the offspring of less well-connected parents can usually gain access to allies and helpers more readily than a landless son in a farming community can acquire land, for example, through savings or systems of patronage. As a result we expect the inter generational transmission of relational wealth to be limited, at least by comparison with material wealth. Embodied wealth is transmitted by a combination of genetic inheritance, socialization, and parent-offspring similarity in the conditions affecting childhood development. The knowledge component of embodied wealth is readily transmitted to offspring, but,cultivar frambuesas unless restricted by religious or other constraints, it is typically available to other members of a population as well . Genetic and psychometric evidence from industrial societies suggests that parent-offspring transmission of economically relevant personality and behavioral characteristics, such as risk-taking, trustworthiness, conscientiousness, and extroversion is limited . We do not have similar evidence across generations in the small-scale populations under study, but industrial-society estimates support our expectation that the degree of inter generational transmission will differ markedly among our three wealth classes, with substantial transmission of material wealth and more limited transmission of relational and embodied wealth. Ethnographic evidence suggests that the four economic systems also differ in the importance of the three classes of wealth. A successful hunter gatherer or horticulturalist depends heavily on his or her strength, practical knowledge, and social networks, while making little use of material resources that are not in the public domain. By contrast, the well-being of a herder or farmer is closely tied to the amount of stock or land under his or her command, which makes material wealth a more important influence on livelihoods in these economic systems.To estimate our model of wealth transmission, we need two pieces of information: the degree of inter generational transmission for each wealth type and the importance of each wealth class in a given economic system . Note that we do not require identification of the causal paths by which transmission takes place, as might be represented in a multi-equation structural model . Our model instead requires a single estimate of the magnitude of the statistical association between parental and offspring wealth for each data set. This requirement, along with the absence of robust evidence of non-linearities, motivated our consistent use of linear models. Functional forms, estimation procedures, robustness checks, weighting procedures, and other aspects of our statistical techniques and results are described in , section 1. Note that the populations studied were not selected at random; instead, we included all populations we were aware of for which inter generational wealth transmission estimates are feasible and the researchers agreed to share data. Table 1 presents our individual estimates of b; Table 2 presents the summary statistics for both the inter generational transmission and the importance of the three wealth classes in the four economic systems.

Across the four economic systems, the estimated b for 14 measures of material wealth, including agricultural and horticultural land, livestock, shares in sea mammal–hunting boats, quality of housing, and household utensils averages 0.37 . For farm land , the degree of transmission is substantial, averaging 0.45 , thus equaling or exceeding the inter generational transmission of most forms of wealth in modern industrial economies . Livestock are even more highly transmitted across generations . Our 23 estimates of the transmission of embodied wealth across generations average 0.12. The highest estimates are for body weight . We also find a very modest level of inter generational transmission of reproductive success ; it is entirely absent in three societies, has a maximum value of 0.21, and averages 0.09, similar to low correlations between parental and offspring fertility in many pre-demographic transition populations . Grip strength is weakly transmitted across generations. The transmission of hunting success is highly variable , averaging 0.17. Knowledge and skill, such as the production and management of horticultural crops in the Pimbwe or proficiency in subsistence tasks and cultural knowledge in the Tsimane, are only weakly transmitted from parents to offspring. The six estimates of relational wealth transmission indicate that the extent to which network links are transmitted across generations is modest, averaging b = 0.19. To measure the importance of each wealth class in the four economic systems we used ethnographers’ judgments of the percentage difference in household well-being associated with a 1% difference in the amount of a given wealth class, holding other wealth classes constant at the average for that population, and requiring these percentage effects to sum to one. The average values of a by wealth class and economic system also appear in Table 2. Consistent with descriptive ethnographies of these and other populations, embodied and relational wealth are relatively important for hunter-gatherers, whereas material wealth is key in pastoral and agricultural populations. Statistical estimates of the importance of each class of wealth across the economic systems would have been preferable, but are precluded by the absence for most populations of a single relatively homogeneous measure of well-being. However, we were able to econometrically estimate m—the importance of material wealth—from an equation similar to using data from populations not represented in our study, including one horticultural, two pastoral, and seven small-scale agricultural economies. These estimates [see section 1] are close to our ethnographers’ estimates and suggest that, if anything, we have understated the difference in the importance of material wealth between pastoral and agricultural economies, on the one hand, and horticultural economies on the other. Correcting this understatement would only strengthen our main conclusions.Our first finding is that the a-weighted averages of the b values for the four economic systems differ markedly . Inter generational transmission of wealth is modest in hunter-gatherer and horticultural systems and substantial in agricultural and pastoral systems. However, even the smaller b values of the former imply that being born into the top 10% of the wealth distribution confers important advantages. In these societies, a child of parents in the highest wealth decile is on average more than three times as likely to end up in the top decile as is the child of the bottom decile. Although hardly a level playing field, inter generational transmission in these economic systems is modest when compared with the agricultural systems, where the child of the top decile is on average about 11 times more likely than the child of the poorest decile to end up in the richest decile, or to the pastoral systems, where the ratio exceeds 20.

The widest plant diameter was from plants grown in the peat and perlite system

The primary justification for using this system is that strawberry crops canbe produced without fumigation ; although if the soilless media could be disinfested and recycled, instead of discarded at the end of each cropping cycle, it would, in theory, represent a more sustainable system. Additional advantages include the ease of attracting harvest labor due to the high fruit yield per linear foot of bed row, and the ability to leave the beds in place for several crop cycles. One of the disadvantages is that coir and peat substrates are expensive and of limited quantity. However, composted wood fiber and composted pine bark have shown good results as substrates and are available locally and are generally less expensive . Logistical issues such as substrate costs and the delivery and installation of large amounts of substrate material have yet to be addressed in U.S. systems. Field trials of a raised bed trough system were carried out at Monterey Bay Academy, near Watsonville, and at Mar Vista Berry, near Santa Maria, from fall 2010 to summer 2011. The studies were set up in randomized complete block designs consisting of five treatments replicated four times. The treatments were 100% coir , a 70:30 peat and perlite mixture, an amended soil mix of 50% steamed soil plus 25% rice hulls and 25% coir, a standard fumigation treatment , and an untreated, non-fumigated control. Harvesting was done from April 28 to Sept. 15, 2011 , and April 13 to Oct. 4, 2011 . The fruit was sorted into marketable berries and cull . Periodic collection of substrate samples was done to monitor pH, electrical conductivity , nitrate nitrogen , ammonium nitrogen and available phosphorus . All data were subjected to analysis of variance ,macetas de plastico 30 litros and Fisher’s protected LSD at 0.05 was used to compare means. Table 1 shows the plant diameters and yields of strawberry crops grown in the plots at Monterey Bay Academy and Mar Vista Berry.

There were highly significant differences in plant diameter and yield of strawberries grown at Monterey Bay Academy.The three substrate treatments did not significantly differ in marketable yield. The untreated, non-fumigated control treatment had the smallest plant diameter and lowest marketable yield. The marketable yield of the coir, peat and perlite, and steamed soil with amendments treatments was 27%, 29% and 13% higher, respectively, than the yield from the standard fumigated treatment. At Mar Vista Berry , the widest plant diameters were in the steamed soil with amendments plots and the peat and perlite substrate plots . However, the substrate treatments did not affect the marketable fruit yield. Significant differences were noted only on the cull yield. The highest cull yield was observed in the steamed soil with amendments; this was the case at both Mar Vista Berry and Monterey Bay Academy, and it could be attributed to the very low pH and high EC of this substrate. One of the main concerns in soilless strawberry production is the maintenance of a favorable pH, EC and nutrient supply to the growing plants. For most of the sampling periods at the experimental sites, different substrate and soil treatments had significantly different levels of pH, EC, nitrate nitrogen, ammonium nitrogen and available phosphorus. At both sites, the pH of the coir and the peat and perlite treatments was lower in the early sampling periods but increased with time, reaching the targeted value of 5.7 after 3 to 4 months ; this slow rise in pH to the target value was attributed to the high nutrient adsorptive capacity of the soilless substrates. The pH of the amended soil treatments at both sites was generally low at all sampling periods, and the target value was not reached during the production cycle. With the exception of the initial sampling period, the EC of the substrate treatments at Monterey Bay Academy was generally low . In contrast, the EC in the Mar Vista Berry beds was consistently high, which could be due to the higher amount of salts in the irrigation water.

The EC of the steamed soil with amendments treatment at Mar Vista Berry was also consistently high throughout the growing season. The soilless substrates are low in nutrients; thus, fertilization is one of the key issues in these systems. Surprisingly, the initial nitrate nitrogen of the coir and the peat and perlite mixture was higher at both sites, and the target value of 100 ppm was maintained in the beds through the season except for the latter stages of plant growth . The standard fumigated beds had generally low nitrate nitrogen. At all sampling periods, the ammonium nitrate was lower than the RABETS target value of 14 ppm . The RABETS target of 30 ppm available phosphorus was maintained in all of the media treatments at both sites .Anaerobic soil disinfestation , a nonchemical alternative to methyl bromide, was developed in Japan and the Netherlands to control soil borne pathogens and nematodes in strawberries and vegetables. Anaerobic soil disinfestation integrates the principles of solarization and flooding in situations where neither method alone is effective or feasible. Anaerobic soil conditions are created by incorporating readily available carbon sources into topsoil, covering the soil with plastic tarp and irrigating to field capacity. The tarp is left in place to maintain soil moisture above field capacity and to sustain anaerobic conditions. Anaerobic decomposers respire using the added carbon, which results in a buildup of anaerobic byproducts that are toxic to pathogens . These byproducts degrade rapidly once the tarp is removed or holes are punched through the tarp for planting. Studies were conducted during 2008 to 2011 in an attempt to optimize anaerobic soil disinfestation for California strawberry and Florida vegetable production systems. Overall, it was very effective in suppressing Verticillium dahliae in soils, and it resulted in 85% to 100% of the marketable fruit yield observed with fumigated controls in coastal California strawberries when 9 tons per acre of rice bran was preplant incorporated and 3 to 4 acre-inches of irrigation was applied in sandy loam to clay loam soils . In the semitropical climate of Florida, when composted broiler litter and heavy black strap molasses were incorporated as substrate, anaerobic soil disinfestation treatments provided good control of nutsedge and excellent control of grasses, broad leaf weeds, Phytophthora capsici and Fusarium oxysporum f. sp. lycopersici .

In the cooler conditions of the Central Coast, however, anaerobic soil disinfestation may not provide effective control of many weed species . To ensure consistency of pest suppression across varying locations, the effects of soil temperatures and treatment length and the mechanisms of pest suppression by anaerobic soil disinfestation are being further elucidated. Its integration with other non-fumigant approaches may also have promise. For example, a combination of anaerobic soil disinfestation and mustard seed meal application is currently being tested .Heat treatment with steam can be used for soil sterilization or pasteurization . Studies have shown that most plant pathogens, insects and weeds will die when moist soils are heated to temperatures higher than 150°F for 30 minutes . The duration and amount of steam needed to raise the soil temperature to 150°F depend on various soil factors, including texture,cultivo hidroponico type and moisture content. Minuto et al. found that soil could be heated most rapidly at a moisture content between 8.5% and 12% in a sandy loam and between 6% and 7% in a sandy soil. Steam applied to field soil that raised the temperature to 158°F for 20 minutes resulted in weed control comparable to methyl bromide . In addition to pest control, an advantage of steaming is that it lacks the negative environmental and worker health issues associated with chemical fumigants. Some have reported that steaming has little or no lasting negative impact on soil quality or soil microbial communities as opposed to the known potential impact of methyl bromide fumigation on both soil quality and microbes . Other studies have reported a more significant change in soil microbial activity due to steam sterilization . Differences among steam studies may be related to duration of steam application and soil temperatures attained during steam treatments as well as the soil organic matter content. Steam has also been shown to increase crop growth and yields . Previous work found that strawberry fruit yields from steam-treated soils were similar to those from soils fumigated with methyl bromide plus chloropicrin .Natural products such as mustard seed are being evaluated as biofumigants. Recent studies found that mustard seed meal amendment can suppress root infection by Rhizoctonia solani . We have been testing mustard seed meal in strawberry beds at rates of 500 to 4,000 pounds per acre incorporated into the soil. Mustard meal alone does not consistently produce high fruit yields or control weeds . One possible method to enhance solarization is to use combinations of mustard meal, chloropicrin, and metam sodium treatments . By heating the soil with solarization or steam, the pest control activity of metam sodium, chloropicrin or mustard meal may be higher than at ambient soil temperatures.

A field study was conducted at Monterey Bay Academy from October 2010 to September 2011 to evaluate anaerobic soil disinfestation and steam with and without mustard seed meal application prior to planting strawberry beds. Treatments included a control; Pic-Clor 60 at 300 pounds per acre as a standard; mustard seed meal at 3,000 pounds per acre; anaerobic soil disinfestation with rice bran at 9 tons per acre; anaerobic soil disinfestation with rice bran at 7.5 tons per acre and mustard seed meal at 3,000 pounds per acre; steam; and steam plus mustard seed meal at 3,000 pounds per acre. The trial was arranged in a randomized complete block design with four replicates. Anaerobic soil disinfestation was initiated Oct. 7 to create a saturated condition. The plots were maintained above field capacity with intermittently applied irrigation water from Oct. 8 to Nov. 3, 2010. Steam was applied via spike injection from a stationary steam generator for a sufficient time to raise the soil temperature to 158˚F for 20 minutes on Oct. 13 and 14, 2010. Weed densities were measured in 25-square-foot sample areas covered with clear tarp, on Dec. 15, 2010, Jan. 21, Feb. 23 and April 6, 2011. Strawberry fruit was harvested weekly from April 28 to Sept. 15, 2011. Fruit was sorted as marketable and cull at each harvest date. Data were subjected to analysis of variance and means were separated using Fisher’s protected LSD.Overall, the steam treatment and the steam treatment with mustard seed meal were as effective as Pic-Clor 60 in providing weed control . Anaerobic soil disinfestation plus rice bran suppressed weed densities, but it was less effective than Pic-Clor 60. No strawberry plant injury was observed in any of the treatments . Marketable yields data collected from April 28 to Sept. 15, 2011, indicate that strawberry fruit yields in the steam treatments and the anaerobic soil disinfestation treatments were comparable to those in the Pic-Clor 60 application . These data, along with data from our prior studies, show that steam is as effective as chemical fumigation; and that anaerobic soil disinfestation also produces yields equivalent to Pic-Clor 60 but may need to be combined with herbicide use in severely weed-infested sites. The costs of the anaerobic soil disinfestation treatments with rice bran, and with rice bran plus mustard seed meal, were $1,632 and $3,093 per acre, respectively, including material, spreading, incorporation and irrigation . The cost of steam was $10,440 per acre, compared to $1900 per acre for Pic-Clor 60. Therefore, although the yields and gross revenues were comparable across treatments, the net returns after treatment and harvest costs were highest for the Pic-Clor treatment, followed by the anaerobic soil disinfestation with rice bran. The lowest net revenue was for the steam plus mustard seed meal treatments due to the high cost of the steam treatment. The cost data showed a critical need for more-efficient steam injection systems before steam can be adopted commercially. Recent advances with steam application equipment can reduce the cost of steam treatment to less than $5,500 per acre with the potential for further cost reductions . Since 2011 we have used an automatic mobile steam applicator in our research, which lowers the labor costs relative to those reported here by approximately 50% to 70%. It mixes steam with soil, allowing soil to be heated from 60˚F to 160˚F in 90 seconds — much more rapidly than the steam application system used here .

The linear model for the Nema Quad system had the steepest slope but not a very strong R-squared value

Even though no significant differences were detected with the ANOVA analysis, linear models were weak at representing the relationship between fruit size and fruit per hectare and all systems using size-controlling root stocks had an R-squared value <0.15 . Continuing the trend from the previous season, in 2019 for June Flame, there were no significant differences in the slope of fruit size vs fruit per hectare relationship for any of the systems . The contrast between the C-6 Quad system and Nema Quad system did have a t.ratio with a greater absolute value than 1.68, however the P.value for the same comparison was still greater than the designated alpha, > 0.05. In this same season the C-6 Quad system had the best fit for the linear model showing a negative correlation between fruit size and fruit per hectare. All other systems fit the model poorly and also did not indicate a clear negative correlation between fruit size and fruit count per hectare . For the August Flame harvest of 2017, data from all systems fit linear models that showed a negative correlation between fruit size and fruit per hectare . Values for the t. ratio between the C-9 Quad and Nema Quad systems were beyond the absolute limit but had a P. value greater than the declared alpha, thus no significant differences were confirmed .For the 2018 harvest of August Flame there were no significant differences in the fruit size vs. fruit per hectare relationships detected among systems . Linear models fit 2018 August Flame data better than other years and showed a clear negative correlation between fruit size and fruit per hectare . In 2019 there was a wide spread of mean fruit sizes per tree in the August Flame data and no significant differences occurred among systems for the relationship between fruit size and fruit per hectare . Although the ANOVA analysis did not indicate differences among systems,hydroponic nft system linear models indicated a weak negative correlation between fruit size and fruit per hectare with all systems having near horizontal models accompanied by Rsquared values <0.1 . Although R-squared values for the linear models representing the relationship between fruit size and fruit per hectare were identical to those for fruit size and fruit per tree , there were differences detected in the contrast analysis for slopes.

Data for the June Flame 2017 and 2018 harvest seasons indicated no significant differences in the relationship for fruit size vs fruit count per tree among any of the systems . In 2019 there was a significant difference in the data for the June Flame cultivar between the C-6 Quad system and the Nema Quad system . In the 2017 harvest data of August Flame there was a significant difference in the fruit size vs. fruit per tree relationship among C-6 V and Nema Quad systems . The difference in 2017 data was visually apparent in the steeper slope indicated in the C-6 V system but that might be a result of the narrow range of fruit loads per tree in that system . No significant differences in the fruit size vs. crop load per tree relationship were detected in the harvest season of 2018, however both, C-6 Quad and C-6 V systems, had t. ratios indicating one may exist, but p-values remained above alpha, therefore a difference was not conclusive . Data for the 2019 harvest of August Flame indicated no significant differences in this relationship between systems, and in fact, the fruit size vs. crop load per tree relationship were most similar among systems in this year compared to other years .A relationship between light interception and yield was most apparent in the June Flame cultivar with the C-6 Quad and C-9 Quad systems which produced data that fit linear models with the highest R-squared values.Data from the C-6 V system had a poor fit with a linear model. Interestingly the systems with data that had a poor fit to the model also had the highest % light interception, often >50% . August Flame cultivars showed a similar pattern for the relationship between amount of light intercepted and yield. Data from the Nema Quad and C-6 V systems had poor fits to the linear models but also had the highest light interception. Data from the C-9 Quad system had a moderate correlation between PAR and yield, fit the model best.

The C-6 Quad system is an apparent outlier, having a value of almost 5 Kg/m2 yield with only about 40% light interception, and a very slight negative correlation between the two parameters . Both of the C-6 V systems with the June and August flame cultivars had trends as shown in previous research, higher density systems were able to intercept a higher proportion of light during earlier years because the trees fill their allotted space more quickly, . The mean fruit size for the June Flame cultivar in 2017 was similar among all systems, most likely a result of consistent thinning resulting in the desired crop loads per tree. In 2018 the mean fruit size for June Flame systems was exceptionally large, especially for an early bearing cultivar. Considering that the C-6 Quad and C-6 V systems had some of the largest fruit sizes provides strong evidence that size-controlling root stocks are not always associated with reductions in fruit size. The C-9 system had poor performance in the trial but, with its success in previous studies and how well systems with the more size controlling root stocks performed in this trial, it is likely not due to the reduced hydraulic conductance associated with size controlling root stocks . June Flame systems in 2019 closely mirrored fruit sizes from the previous season, providing more confidence that any reduction in fruit size compared to the Nema Quad system is unlikely a result of size controlling root stocks. The results from the June Flame cultivar are most promising because there were concerns that the size-controlling root stocks may have the potential to have negative effects on fruit size in early maturing cultivars. With how quickly early bearing cultivars must set and mature fruit during the spring flush growth, there was concern that reduced hydraulic conductance associated with undeveloped xylem would influence fruit size . However, this trial did not provide evidence that early maturing cultivars on the size-controlling root stocks produce smaller sized fruit compared to those on more vigorous root stocks.

With the August Flame cultivar, systems using size-controlling root stocks also were not found to diminish fruit size in this later maturing cultivar. In 2017 all dwarfing systems performed beyond expectations. With fruit sizes reaching almost 300 grams, it is likely that thinning may have been excessive and crop load per tree could have been increased while still reaching above minimum fresh market size requirements. The strong yield for high density plantings of August Flame during the 2017 harvest supports reports of higher density plantings reaching full cropping sooner than low density systems . By 2018 the Nema Quad systems were able to produce fruit of similar size compared to systems with size-controlling root stocks, but fruit were still not the largest. Large fruit sizes indicate that the amount of thinning could, again, have been reduced. In 2019 there was noticeable water stress in the field due to some irrigation problems,nft channel but the magnitude of the problem was not documented. It is likely the water stress was a reason for some of the smaller fruit sizes compared to previous years. Most interesting about the 2019 season was the performance of the C-9 Quad system and how after producing significantly smaller and fewer fruit in both previous seasons, it now had the largest mean fruit size. Overall, systems with size-controlling root stocks performed well and on par compared to the Nema Quad system giving confidence that reduced hydraulic conductance associated with size-controlling root stocks does not necessarily reduce fruit size in either early or late bearing cultivars such as June and August Flame.In addition to fruit size, number of fruits produced was not diminished in systems using size controlling root stocks compared to the Nema Quad system. The 2017 harvest for the June Flame cultivar was the only harvest that the Nema Quad system produced significantly more fruit per hectare than all other systems. These results differ with previous studies where KAC_V plantings reached full cropping at the same time as trees on vigorous root stocks but, systems with size-controlling root stocks pruned to an open-vase lagged behind more vigorous root stocks . By 2018 the C-6 Quad and C-6 V systems produced more fruit per hectare than the Nema Quad system while the C-9 system had a substantially reduced yield compared to all other systems. Fruit count could have been increased had thinning been more consistently managed but since fruit sizes were also similar, results would not likely have changed in terms of differences between systems. 2019 was by far the most productive harvest for June Flame, with strong yields in the C-6 Quad, C-6 V, and Nema Quad systems while the C-9 Quad was less productive. Due to the lack of significant differences among systems there is no evidence that a reduction in either fruit size or fruit count would be expected in an orchard system using size-controlling root stocks compared to a system with more vigorous root stocks, when using appropriate management practices and planting densities adjusted for the reduced tree size.

Results from the 2017 harvest of August Flame were much more aligned with previous studies where systems with high-density plantings reached maximum yield capacity earlier than in low-density systems . It is possible that if the amount of thinning in the C-6 Quad and C-6 V systems had not been as severe, they could have produced significantly more fruit than the Nema Quad system. The C-9 Quad system had the lowest fruit count but, with such a large fruit size, could have potentially produced a fruit count similar to the Nema Quad system if thinning had been done more precisely. In 2018 the fruit count was similar in the C-6 Quad, C-6 V, and Nema Quad systems while the C-9 Quad system had half the crop load as the other systems. Since the most size-controlling root stocks produced yields on par with the Nema Quad system, it is probable that the C-9 Quad system was under some stress that hindered production rather than its reduced fruit count being a result of reduced hydraulic conductance in the root stock. It is likely in 2019 that all systems were under stress. Not only was fruit size significantly smaller than previous years, fruit count per hectare was also fewer than that of even the earlier bearing cultivar for all systems except the C-9 Quad. It is widely accepted that as crop load increases fruit size diminishes . In this study the relationship between crop load and fruit size was similar among systems with high density plantings on size-controlling root stocks and the system with lower planting densities on a vigorous root stock. Results were as expected, as crop load increased fruit size diminished. Although the relationship between fruit size and fruit produced per hectare was not significantly different among systems, appropriate crop load per tree and fruit size was influenced by planting density. The larger crop load that trees in the Nema Quad system could hold while maintaining similar fruit size as trees from other systems with significantly reduced crop load per tree indicate that trees with size-controlling root stocks planted at a higher density may not be able to maintain as large of fruit size with larger crop loads compared to trees with more vigorous root stocks at wider spaced plantings, this concurs with findings from Inglese et al., . Results from this study also demonstrate that an increased number of trees per unit area compensate for the reduced crop load per tree, thus allowing high-density plantings on size controlling root stocks to be a viable option for commercial production, similar findings have been reported by Webster and DeJong et al., .It is well documented that an orchard’s ability to intercept photosynthetically active radiation influences yield and that the two are linearly related up to 50% light interception .

Plants were evaluated for disease incidence after reaching harvest maturity

Individual weed biomass for A. palmeri and D. sanguinalis, however, was lower for all weed densities when grown in the presence of sweet potato compared with weeds grown without sweet potato. The reduced individual biomass and biomass per meter of row for both weeds, when grown with sweet potato, indicate that interspecific interference is occurring between sweet potato and weeds. Crop biomass reductions are generally associated with increased weed competition and yield losses . However, in this study, although weed biomass was lower when grown with sweet potato, increased weed density did not reduce sweet potato biomass, despite the reduction in sweet potato yield at the same densities.Individual dry biomass of each weed species growing without sweet potato decreased as weed density increased . In the absence of sweet potato, individual dry biomass of both weeds was fit to a linear-plateau model. Individual weed biomass was greatest for both weeds at the lowest density. Amaranthus palmeri and D. sanguinalis individual plant biomass decreased 71% from 1 to 3 plants m−1 of row and 62% from 1 to 4 plants m−1 of row, respectively, and remained unchanged at densities above 4 plants m−1 row for both weeds . This finding was similar to the trend observed in peanut for A. palmeri. We believe that the reduction in individual weed biomass for A. palmeri and D. sanguinalis at lower weed densities when grown without sweet potato is due to increasing intraspecific competition as weed density increases. At the higher densities of both weeds,dutch bucket hydroponic the impact of intraspecific competition has limited effect on further decreasing individual weed biomass. The established threshold is the density at which all weeds achieve maximum accumulated biomass before intraspecific competition begins.

Further biomass increases would require densities resulting in weed mortality due to intraspecies competition, and such densities were not evaluated in this study. This study demonstrates that A. palmeri and D. sanguinalis have the ability to reduce yield at densities as low as 1 to 2 plants m−1 row. Sweetpotato competes with A. palmeri or D. sanguinalis, resulting in reduced weed biomass. This observation suggests that sweet potato with rapid canopy establishment and dense growth habit may provide additional competition with weeds and reduce yield loss, as proposed by Harrison and Jackson . Future studies should establish critical weed-free periods for these weeds in sweet potato, investigate competitiveness of resistant weed biotypes with sweet potato, and determine weed interference with sweet potato under varying management practices .The Salinas and Pajaro Valleys of coastal central California are among the most important lettuce-producing regions in the United States. One of the top disease concerns for lettuce in the area is Verticillium wilt caused by the fungus Verticillium dahliae, which is a soilborne pathogen with a wide host range that also includes artichoke, cotton, eggplant, hops, potato, sunflower, tobacco, and tomato. Two races of V. dahliae occur in coastal central California based on their differential virulence on cultivar La Brillante; however, race 1 is more prevalent and economically important than race 2. In tomato, race 1 of V. dahliae carries Ave1 that is recognized by Ve1 in resistant genotypes. Ve genes encode receptor-like proteins with extracellular leucine-rich repeats; such RLPs are widespread in land plants. In addition to Ve1, tomato also contains the closely linked paralog Ve2; their encoded RLPs work antagonistically to confer resistance to V. dahliae race 1. Several Ve paralogs also confer resistance in otherwise V. dahliae-susceptible species including cotton, potato, hops, and wild eggplant, but it is unknown whether they function analogously to the tomato Ve genes in conferring V. dahliae race 1resistance. In lettuce, resistance to V. dahliae race 1 was originally identified in the Batavia-type cultivar, La Brillante, as conferred by a single dominant locus located on chromosomal linkage group 9. The lettuce Vr1 locus contains several genes with sequence similarity to the Ve genes of tomato; it is very likely that one or more of these LsVe homologs are functional resistance genes.

The goals of this study were to identify the lettuce Ve allele that play a role in resistance to V. dahliae race 1 and to develop PCR-based assays for marker-assisted selection. For this purpose, we analyzed the genome sequences of cultivars La Brillante and the previously published Salinas. Subsequently, we sequenced and/or used allele-specific PCR screens of 150 additional lettuce accessions to identify the allele of the LsVe genes that are exclusively present in resistant phenotypes.Cultivar La Brillante is a Batavia type lettuce with a small, round head that is less dense than those of modern iceberg cultivars. Because of the certain phenotypic similarities in the shape of heads, fewer back crosses are usually needed to develop true to type iceberg cultivars when introgressing desirable genes from Batavia accessions than would be needed if those genes were introgressed from non-heading types of lettuces. Our current analyses showed that besides cultivar La Brillante, another Batavia cultivar can also be used for a relatively rapid development of iceberg cultivars with resistance to V. dahliae race 1. Both of these cultivars contain the same combination of LsVe alleles . Only two out of 36 romaine accessions were resistant to the disease in field experiments. One of the resistant accessions, cultivar Annapolis, is a dark red lettuce with a relatively small and light head that is usually grown for baby leaf production and is therefore harvested at early stages of development. The other resistant cultivar was Defender, which is green. Origin of resistance in this cultivar is unknown because it was developed through open pollination. A high frequency of resistance to the disease was found in Latin type accessions thatphenotypically resemble a small romaine lettuce with more pliable and oily leaves. Because of the phenotypic similarity between romaine and Latin types, Latin-type accessions may also be used for a relatively rapid development of romaine cultivars with resistance to V. dahliae race 1. Both romaine cultivars and three sequenced Latin cultivars that are resistant to the disease contain an identical combination of LsVe alleles . Substantially different frequencies of LsVe1L alleles and resistant phenotypes in different horticultural types of lettuce are not unexpected considering that comparable differences were previously described for other monogenically inherited traits, such as resistance to lettuce dieback and sensitivity to triforine.

Differences in the frequency of specific alleles among horticultural types are likely caused by the breeding approach that is used to develop lettuce cultivars. Only a few elite progenitors or founder lettuce cultivars have given rise to most of the modern commercial cultivars. Each of these progenitors is frequently found in pedigrees of cultivars of the same horticultural type. Additionally, new cultivars are mainly developed by recurrent breeding within small pools of closely related germplasm of the same type. Therefore, alleles present in an original progenitor of a certain type are found in high frequency in cultivars of the same type, but may be absent or present in low frequency in cultivars of other horticultural types. Our data are consistent with the LsVe1 gene identified in the cultivar La Brillante being involved in resistance to V. dahliae race 1 in lettuce. Among the 152 accessions included in this study, 21 were resistant to V. dahliae race 1 and all 21 contained the LsVe1L allele; this allele was not present in any of the susceptible accessions. The other La Brillante Ve alleles, LsVe3L and LsVe4L,blueberry grow pots were also present in all the resistant accessions, but they also occurred in two and twelve susceptible accessions, respectively. Therefore, LsVe1L is the strongest candidate as being required for resistance to V. dahliae race 1 in lettuce, although our data do not exclude LsVe3L or LsVe4L from also being involved similarly as in tomato. Complementation and knock-out studies are still required to determine the functional basis of LsVe-mediated resistance to V. dahliae race 1. The function and the significance of the differences between the LsVe1L and LsVe1S alleles remains to be investigated. The proteins encoded by LsVe1L and LsVe1S have the same domain organization, including the 37 extracellular, leucine-rich repeats separated by a short spacer region, as in previously characterized functional Ve proteins in other species. However, in addition to sequence diversity in the extracellular LRR domain, LsVe1L has an additional Cterminal transmembrane domain as compared to Ve1 and Ve2 in tomato, suggesting that maybe LsVe1L crosses the membrane three times and terminates with anon-cytoplasmic domain instead of a cytoplasmic domain. The distribution of disease incidence in susceptible accessions and across horticultural types indicates a possible presence of a modifying factor or factors that affect disease incidence. Our data do not exclude the possibility of interactions between two or more Ve genes, similar to those reported in tomato. A more detailed study of accessions with different frequencies of disease incidence and allelic compositions is needed to elucidate the basis of variation in disease incidence.Experiments were conducted in a field infested with V. dahliae race 1 located at the USDA-ARS station in Salinas, California. One hundred and fifty accessions were direct-seeded in a randomized complete block design with three replications. The original seed batches of previously sequenced cultivars Salinas and La Brillante were not available for field tests; therefore, seed batches used in field tests are shown as separate entries . Each plot was 7 m long and consisted of two seed lines on 1 m wide beds standard for lettuce production in coastal California.

Plant spacing was approximately 28 cm between seed lines and 30 cm between plants within a seed line. All field experiments were maintained using standard cultural practices for coastal California lettuce production.Unless indicated otherwise, ten plants from each plot were uprooted and visually evaluated. Disease incidence was assessed by cutting taproots longitudinally and recording the number of plants exhibiting the yellowish-brown discoloration of root vascular tissues that is typical of Verticillium wilt. Absence of V. dahliae race 1 in cultivars with race 1-resistant genotype was confirmed by plating surface-sterilized symptomatic root tissue on NP-10 semi-selective agar medium and PCR screening any resulting isolates with Ave1-specific primers. Three additional experiments were performed in the same field to confirm phenotypic observations. These experiments comprised only a subset of accessions that were either symptomless in the first experiment or were used as susceptible checks. Disease incidence values from all four experiments were combined and used for statistical analyses with JMP 14.2 .Intracellular transport of plant viruses during infection operates via unique interactions between viral proteins and selected host cytoskeletal and membrane elements. Microtubules and/or actin filaments are required for host cytoskeleton functions that are involved in virus replication and movement . Virus infections often result in modification of these systems and mechanisms affecting these processes have become special topics of enquiry over the past decade . For example, the roles of cellular remodeling in formation of replication factories and intracellular movement of several viruses has been reviewed recently . Since these reviews, the Potato virus X triple gene block 1 movement protein has been shown to remodel actin and endomembranes to form X-bodies that function in replication, and to recruit the TGB2 and TGB3 proteins to the X-bodies . Also, the endoplasmic reticulum and Golgi apparatus have been shown to be extensively remodeled as a consequence of Turnip mosaic virus infection . Modified actin filaments and the endomembrane system are involved intracellular and intercellular movement of several plant viruses . The plasma membrane and ER are continuous between cells, and form desmotubule conduits for intercellular movement of macromolecules between adjacentcells that are regulated by actin filaments, myosin-motor associations, and/or poorly understood membrane flow mechanisms . Virus studies over the past decade have shown that plasmodesmata connections forming cellular symplast boundaries are remarkably plastic and are involved in numerous complex interactions required for virus transit . Considerable variation is now apparent in mechanisms of virus intercellular movement, and this is most evident in viruses in which nucleoprotein complexes move through enlarged PD, versus viruses in which remodeled tubular PD function in cell-to-cell transit of whole virions . All plant viruses encode movement proteins that function in cell-to-cell movement, but these proteins and the pathways involved in movement vary enormously in their complexity and host component interactions . The most intensively studied MPs are Tobacco mosaic virus 30K protein, TGB proteins encoded by hordeiviruses and potexviruses, the Closterovirus movement complex proteins, the Nepovirus 2B protein, and the P6 Cauliflower mosaic virus . Each of these MP complexes interact in a variety of ways with endomembrane components, cytoskeleton networks and PD .

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