Alternative extrapolations of the same data were subsequently published that accounted for differences in foliage turnover rates between biomes, significantly lowering the global strength of a putative aerobic plant source . To further constrain the potential magnitude of global CH4 emissions from upland plants, we used a foliar VOC emissions model—MEGAN or Model of Emissions of Gases and Aero sols from Nature—to incorporate certain canopy and physical processes that were not considered by Kirschbaum et al. and Parsons et al. . In particular, we used the temperature responses reported by Keppler et al. and accounted for the effects of self-shading within the plant can opy. We used MEGAN with the assumption that the mechanism of CH4 production, if it exists at all, shares some features of the biochemical pathways that produce other VOCs such as methanol. MEGAN includes a detailed canopy environment model that calculates solar radiation and leaf temperature of sun and shade leaves for each of five canopy depths. Driving variables include wind speed, humidity, soil water content, above-canopy direct and diffuse solar radiation, and ambient temperature. MEGAN includes emission factors for light-de pendent and light-independent components of emissions, and irradiances that vary because of self-shading in the plant canopy. Light-dependent and light-independent emissions of CH4 were estimated based on the emission factors recommended by Keppler et al. . Although Keppler et al. did not report light response curves,maceta 30 litros we assumed that emissions increase nearly linearly with irradiance to a saturation point. This is the behavior we observe for other biogenic VOC and is thus a reasonable starting point for the CH4 extrapolation.

The emission algorithm for dark emissions was based on the temperature response shown in Figure 1 of Keppler et al. . A range of global annual CH4 emission estimates was generated using different combinations of the alternative land cover and weather databases described by Guenther et al. . Our parameterization of light and temperature in the MEGAN model is similar to the global model of aerobic CH4 emissions developed by Butenh off and Khalil . The global distribution of CH4 emissions from foliage simulated with MEGAN is shown in Figure 1. Tropical forests are a major source region, which agrees with the predictions of Keppler et al. and the observations of Frankenberg et al. . The annual global CH4 emission from living vegetation estimated with MEGAN ranged from 34–56 Tg year –1, depending on the land cover and weather data used to drive the model. This figure is nearly one order of magnitude lower than the highest estimates provided by Keppler et al. and is consistent with the magnitude of alternative extrapolations provided by Kirschbaum et al. and Parsons et al. , and the global model developed by Butenhoff and Khalil . Our estimates would be about an order of magnitude lower if we had used the mean rate reported by Dueck et al. of 21 ng g–1 h–1.The demand for nutritious and safe food will increase as the human population is expected to reach between 9.4 and 10.1 billion in 2050 and between 9.4 and 12.7 billion in 2100 , along with increasing urbanization and standards of living . Healthy consumption of grains, oil seeds, nuts, and fresh fruits and vegetables is part of an integrated strategy to decrease the risk for diet-related chronic diseases, such as cardiovascular disease, type 2 diabetes, some types of cancer, and obesity . However, the World Health Organization report shows that at global level, 31 hazards caused 600 million food borne illnesses and 420,000 deaths in 2010 . Health concerns exist due to the consumption of mycotoxins produced by fungi that frequently infect grain, oil seed, and nut crops . The health burdens placed on consumers and economic burdens placed on farmers and processors by the presence of these toxins can be severe . Furthermore, heavy metals , allergens , and accumulations of natural molecules and compounds may be detrimental to human health.

At the same time, the number of food borne disease outbreaks related to consumption of contaminated fresh or minimally processed produce has been increasing . In the United States, 48 million illnesses and 3000 deaths associated with food-borne diseases occur annually, with approximately one half associated with crops . In the European Union, during the period 2004–2012, there were 198 outbreaks linked to the consumption of fresh produce . Beyond the burden on public health, food borne illness outbreaks negatively affect the economics of the industry. It is estimated that the overall cost of food safety incidences for the economy of the United States is $7 billion per year, which comes from notifying consumers, removing food from shelves, and paying damages from lawsuits . Furthermore, a single produce-borne disease outbreak can trigger a sharp decrease in the market of the affected crop for years . Following a number of large multistate foodborne disease outbreaks linked to contaminated fresh produce1 , the American Phytopathological Society-Public Policy Board convened the first formal activity in 2007 in a symposium titled “Cross Domain Bacteria: Emerging Threats to Plants, Humans, and Our Food Supply”. A working group on “Human Pathogens on Plants” was assembled to create solutions for this problem and has since convened as a satellite meeting during annual APS meetings. Similar activities have been conducted in Europe through the COST Action on “Control of Human Pathogenic Micro-organisms in Plant Production Systems”. Leafy greens are annually involved in food safety incidents in the United States. From 1996 to 2016, 134 confirmed incidents, including 46 outbreaks, were identified to be linked to products from California that provides one-third of the vegetables and two-thirds of the fruit and nuts in the United States according to the California Department of Agriculture , California Agricultural Production Statistics. During this period, lettuce and spinach were reported as the main vehicles of food safety incidents . After three major outbreaks in 2006, the leafy green industries in Arizona and California created the Leafy Green Marketing Agreement with evidence-based food safety metrics that are updated to incorporate the most current state-of-the-science5 . Likewise, the U.S. Food and Drug Administration subsequently implemented the Food Safety Modernization Act to address the significant public health burden of preventable foodborne diseases.

Under FSMA,frambuesas maceta the Produce Safety Rule established, for the first time, science-based minimum standards that include on farm regulation of fresh fruits and vegetables grown for human consumption. Food safety is a complex issue that requires a concerted effort among scientists, regulators, seed/nursery industry, processors, retailers, and other stakeholders from diverse disciplines and research fields who do not often have the opportunity to meet and discuss global, comprehensive, and objective solutions. On 5–6 June 2019, the University of California, Davis hosted the first workshop on Breeding Crops for Enhanced Food Safety7 to identify knowledge gaps and research priorities in this emerging field to inform the USDA-NIFA and other agencies for funding and research priorities. This workshop connected plant scientists, plant breeders, extension specialists, microbiologists, and food safety experts from industry and academia to discuss collaborative efforts and multidisciplinary approaches geared toward preventing the occurrence of hazardous microbes, mycotoxins, elements, and allergens in crop and food production systems. Together, these pivotal steps by academia, industry, and government groups have laid out the opportunities to enhance food safety with plant breeding and created avenues for unique collaborative efforts and new research directions, which formed the basis for this review. The presence of mycotoxins, elements, and allergens in affected food crops has a high potential for mitigation via plant breeding . These substances, produced by the fungus, the plant itself, or taken up by the plant from the environment, are generally not defense compounds, but can be severely detrimental to the health of humans and animals who consume the crop in which the substances have accumulated. Crop varieties that do not support growth of the fungi that produce mycotoxins have been created in some cases and heritability is sufficiently high for genetic gain in others . Additionally, it may be possible to create host plants that do not allow or create the need for the fungi to produce mycotoxins. The level of allergens in crop plants can also be reduced in some cases via plant breeding, or in others, via genetic engineering or gene editing and breeding for wheat varieties that do not accumulate heavy metals . Furthermore, breeding efforts are conducted for the reduction of antinutritional compounds, such as vicine and convicine in faba bean and the acrylamide-forming potential of potatoes . Mounting evidence suggests that zoonotic bacterial pathogens of humans may have adapted to both animal and plant hosts, enabling them to survive in the food production chain . For example, romaine lettuce and other leafy greens continue to be linked to E. coli O157:H7 outbreaks traced to major leafy green production regions in Arizona and California despite widespread implementation of LGMA food safety practices; moreover, trace back and environmental assessments suggest that contamination is occurring at the pre-harvest level, but root causes remain elusive . A few research groups have discovered phenotypic variability in the interaction between these pathogens and fresh produce, suggesting that plant genetic traits may affect plant susceptibility or tolerance to human pathogen colonization.

A complete description of the methods used in each study is listed in Supplementary Table S1. Similarly to the examples of breeding strategies described above, these reports support the basis for breeding for decreased microbial hazards in several systems. Host plant resistance to the fungi that produce mycotoxins can be a synergistic part of a systems approach to reducing mycotoxins in crop plants . The method is economical for the farmer because it requires no additional equipment or supplies and is integral to the seed itself. It works well with other methods for controlling mycotoxins, including the use of biocontrol agents that farmers can buy and apply to the field, and proper handling and environmental conditions during harvest, drying, and storage, which can also help prevent the growth of the fungi. There has been a long history of breeding wheat for resistance to Fusarium graminearum that produces deoxynivalenol , although complete resistance remains elusive. Significant progress has also been made, for example, in pre-breeding germplasm in maize that does not support the production of aflatoxin or significantly reduces it compared to conventional maize varieties. These traits are being introgressed into U.S. maize inbreds by Paul Williams and Marilyn Warburton at USDA–ARS, Mississippi, and Seth Murray and Wenwei Xu at Texas A&M University. Heritable plant traits that reduce the numbers of harmful human pathogen cells on the edible portions of the plant may also be incorporated into a system designed to reduce risk from these microorganisms without negatively influencing the other components of the system. Similarly, Charlie Brummer and Allen Van Deynze, with support from Richard Smith have identified and are breeding lines of spinach that have reduced accumulation of cadmium, a heavy metal found in some soils in California that can have chronic health effects, especially in children. Wheat varieties that accumulate low levels of cadmium are being developed using the latest genomic and phenotyping technologies . The fresh produce industry faces several major challenges related to controlling risks from in-field contamination of crops by zoonotic enteric pathogens . First, zoonotic fecal-borne pathogens may be widespread in the environment, but rarely detected in field crop, thus making it difficult to precisely define the most important direct and indirect routes of contamination . Second, if bacterial contamination occurs in the field, there is no subsequent “kill step” for many popular produce items such as salad greens that are consumed raw or minimally processed. Third, the infectious dose for these pathogens may be low, especially among vulnerable populations such as young children . Although it may seem improbable that a low level of in-field contamination could result in large numbers of human foodborne illnesses, Danyluk and Schaffner developed a quantitative risk assessment model that predicted that exposure to levels of E. coli O157:H7 in the field—as low as -1 log CFU/g and 0.1% prevalence—could result in a nationwide outbreak in combination with post harvest contributing factors such as cross-contamination during the washing process.