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.