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Global warming poses serious threats and challenges to the production of leafy vegetables. Being a cool-season crop, lettuce is particularly vulnerable to heat stress. To adapt to climate change, this study was conducted to evaluate the performance of leaf lettuce genotypes for heat tolerance by growing them in different locations within California that differ in temperatures during the growing season. Fifteen green leaf and 21 red leaf lettuce genotypes were selected to evaluate their performance under these environments. These genotypes were planted in March and May in Five Points (San Joaquin Valley) and El Centro (Imperial Valley) and in June 2012 in Salinas (Salinas Valley). The results suggest that lettuce planting can be extended from January to March beyond the normal growing seasons in San Joaquin and Imperial Valleys, where yield may be higher than in the Salinas Valley. The further delay in planting date from March to May in Five Points and El Centro resulted in reduction of yield and an increase in susceptibility to bolting and heat-related disorders such as tipburn and leaf desiccation in most genotypes. The susceptibility to these disorders depends on the genotype and the temperature during lettuce growth and maturation. However, heat-tolerant leaf lettuce genotypes adapted to these regions were identified. Results of this research should be useful for the development of heat-tolerant lettuce cultivars and for extending the growing season in warmer but lower land cost areas to reduce production costs. [ABSTRACT FROM AUTHOR]

Altered precipitation patterns and increased water demands from urban, industrial, and environmental needs often reduce the volume of irrigation water available for agriculture. Strategies that reduce irrigation water inputs, e.g., deficit irrigation (DI), need further evaluation to determine potential impacts on yield and soil microbial communities driving critical soil biogeochemical cycles. Whether soil organic amendments can stabilize DI effects on yield and microbial communities remains unknown. Processing tomato beds were established in a full factorial experimental design of soils unamended or amended with a one-time application—four to five years before sampling—of either biochar or biochar with compost and three irrigation regimes: full (100 % of plant water demand), or DI treatments at 75 % or 50 % of full irrigation. We profiled soil bacterial and archaeal community compositions for two growing seasons and determined soil C and N metabolic potentials and biomass of microbial groups using high throughput sequencing of 16S rRNA genes and phospholipid fatty acid analysis. We tested the discrete and interactive effects of DI and soil amendments on soil chemical and biological properties, and crop yield. DI had stronger effects on the bacterial and archaeal community composition than soil organic amendments. However, 75 % DI did not strongly affect bacterial and archaeal community composition or the total and individual biomass of microbial groups, but it increased irrigation water productivity of processing tomatoes. Although soil amendments did not stabilize the compositional shifts induced by DI, their recalcitrant C still had residual effects on the bacterial and archaeal community composition years after their incorporation. Furthermore, soil moisture correlated with bacterial and archaeal community's C and N metabolic potentials, likely augmenting the amendments' C and N residence time in DI soils. Our results provide insight into water-saving mechanisms that could increase profit margins in water-scarce years without affecting microbial populations that support plant growth and productivity. [Display omitted] • Deficit irrigation (DI) shifted microbial composition and biomass more than organic amendments. • Organic amendments did not mitigate negative effects of DI on microbial populations. • Moderate DI increased water productivity without affecting microbial communities. • DI augmented the residence time in of C and N in soils with organic amendments. [ABSTRACT FROM AUTHOR]

The goal of this study was to characterize the bacterial diversity on different melon varieties grown in different regions of the US, and determine the influence that region, rind netting, and variety of melon has on the composition of the melon microbiome. Assessing the bacterial diversity of the microbiome on the melon rind can identify antagonistic and protagonistic bacteria for foodborne pathogens and spoilage organisms to improve melon safety, prolong shelf-life, and/or improve overall plant health. Bacterial community composition of melons (n = 603) grown in seven locations over a four-year period were used for 16S rRNA gene amplicon sequencing and analysis to identify bacterial diversity and constituents. Statistically significant differences in alpha diversity based on the rind netting and growing region (p < 0.01) were found among the melon samples. Principal Coordinate Analysis based on the Bray-Curtis dissimilarity distance matrix found that the melon bacterial communities clustered more by region rather than melon variety (R2 value: 0.09 & R2 value: 0.02 respectively). Taxonomic profiling among the growing regions found Enterobacteriaceae, Bacillaceae, Microbacteriaceae, and Pseudomonadaceae present on the different melon rinds at an abundance of ≥ 0.1%, but no specific core microbiome was found for netted melons. However, a core of Pseudomonadaceae, Bacillaceae, and Exiguobacteraceae were found for non-netted melons. The results of this study indicate that bacterial diversity is driven more by the region that the melons were grown in compared to rind netting or melon type. Establishing the foundation for regional differences could improve melon safety, shelf-life, and quality as well as the consumers' health. [ABSTRACT FROM AUTHOR]

In the western United States, curly top disease (CTD) is caused by beet curly top virus (BCTV). In California, CTD causes economic loss to processing tomato production in central and southern areas but, historically, not in the north. Here, we document unusual CTD outbreaks in processing tomato fields in the northern production area in 2021 and 2022, and show that these were caused by the rare spinach curly top strain (BCTV-SpCT). These outbreaks were associated with proximity of fields to foothills and unusually hot, dry, and windy spring weather conditions, possibly by altering migrations of the beet leafhopper (BLH) vector from locations with BCTV-SpCT reservoirs. Support for this hypothesis came from the failure to observe CTD outbreaks and BLH migrations in 2023, when spring weather conditions were cool and wet. Our results show the climate-induced emergence of a rare plant virus strain to cause an economically important disease in a new crop and location. • Curly top disease (CTD) in the western US is caused by beet curly top virus (BCTV). • CTD affects processing tomato production economically in central and southern California, historically sparing the north. • Unprecedented CTD emerged in northern California in 2021 and 2022, involving a rare BCTV spinach curly top strain. • The lack of CTD in 2023 with cool, wet spring weather conditions highlight climate's role in virus emergence. [ABSTRACT FROM AUTHOR]

Cucurbit leaf crumple virus (CuLCrV) is a geminivirus transmitted by Bemisia tabaci (Gennadius) biotype B (SPW-B) and common in melons (Cucumis melo L.) planted from July through September in the desert southwestern United States. Symptoms include chlorotic leaf spots, leaf curling and crumpling, and interveinal yellowing, and plants may be stunted. Melon breeding line MR-1, and six plant introductions (PIs; PI 124111, PI 124112, PI 179901, PI 234607, PI 313970, and PI 414723) exhibited partial resistance to CuLCrV in naturally infected field tests and controlled inoculation greenhouse tests. PI 236355 was completely resistant in two greenhouse tests. Partially resistant plants exhibited chlorotic spots, or mild expression of other typical CuLCrV symptoms; all such plants were positive for presence of virus using polymerase chain reaction analysis with a CuLCrV-specific primer pair from the BC1 region. Genetic resistance to CuLCrV in melon was recessive. Field and greenhouse data from F1, F2, and backcrosses of the F1 to 'Top Mark' and PI 313970 demonstrated a single, recessive gene for resistance to CuLCrV. Progenies from crosses of four partially resistant cultigens with 'Top Mark' were susceptible. Resistance in PI 313970 appeared to be allelic, with resistance in the other six cultigens based on F1 data. The name cucurbit leaf crumple virus and symbol culcrv are proposed for this gene. [ABSTRACT FROM AUTHOR]

• Metabolite and transcript profiles of melons grown at 7 US locations were analyzed. • Enrichment of esters in TTDV was detected. • Lipid-derivatives were enriched and carotenoids were depleted in honeydew cultivars. • Association analysis identified differential gene expression of transcripts linked to carotenoids and ester level QTLs in TTDV and honeydews. Melon (Cucumis melo) is an important crop grown worldwide. The diversity of aromatic volatiles melon fruits produce contributes to their diverse flavors. However, little is known about the chemical and molecular profiles essential for establishing the signature flavors in field conditions. Here we analyzed the metabolome and transcriptome of 10 melon varieties grown in the field in Weslaco, TX. Also, two cultivars (TTDV and F39) grown at seven locations in the US were studied further to understand how geographic conditions influence levels of metabolites and transcripts. The data obtained here were combined with sensory data, and the relationship between observed metabolites/transcripts and fruit quality QTL was evaluated. Overall, esters and lipid-derived metabolites varied significantly in different sample sets. TTDV variety was significantly enriched for esters, whereas honeydew varieties were for lipid-derived metabolites, separating their profiles from other varieties. Among transcripts associated with cultivar-specific metabolites, we identified several transcripts linked to QTLs responsible for the production of fruit metabolites, including benzyl alcohol O-benzoyltransferase (AAT2) and caffeic acid 3-O-methyltransferase 1-like. On the other hand, transcripts associated with location-specific metabolites did not produce a clear overlap with known fruit-quality QTLs, suggesting the presence of different regulatory systems for the environmental control of fruit metabolites. [ABSTRACT FROM AUTHOR]

Abstract Describing baseline microbiota associated with agricultural commodities in the field is an important step towards improving our understanding of a wide range of important objectives from plant pathology and horticultural sustainability, to food safety. Environmental pressures on plants (wind, dust, drought, water, temperature) vary by geography and characterizing the impact of these variable pressures on phyllosphere microbiota will contribute to improved stewardship of fresh produce for both plant and human health. A higher resolution understanding of the incidence of human pathogens on food plants and co-occurring phytobiota using metagenomic approaches (metagenome tracking) may contribute to improved source attribution and risk assessment in cases where human pathogens become introduced to agro-ecologies. Between 1990 and 2007, as many as 1990 culture-confirmed Salmonella illnesses were linked to tomatoes from as many as 12 multistate outbreaks (Bell et al., 2012; Bell et al., 2015; Bennett et al., 2014; CDC, 2004; CDC, 2007; Greene et al., 2005a; Gruszynski et al., 2014). When possible, source attribution for these incidents revealed a biogeographic trend, most events were associated with eastern growing regions. To improve our understanding of potential biogeographically linked trends in contamination of tomatoes by Salmonella , we profiled microbiota from the surfaces of tomatoes from Virginia, Maryland, North Carolina and California. Bacterial profiles from California tomatoes were completely different than those of Maryland, Virginia and North Carolina (which were highly similar to each other). A statistically significant enrichment of Firmicutes taxa was observed in California phytobiota compared to the three eastern states. Rhizobiaceae, Sphingobacteriaceae and Xanthobacteraceae were the most abundant bacterial families associated with tomatoes grown in eastern states. These baseline metagenomic profiles of phyllosphere microbiota may contribute to improved understanding of how certain ecologies provide supportive resources for human pathogens on plants and how components of certain agro-ecologies may play a role in the introduction of human pathogens to plants. Highlights • At the time measured, bacterial profiles from the phyllosphere of California tomatoes were completely different than those of Maryland, Virginia and North Carolina (which were highly similar to each other). • As environmental pressures on plants (wind, dust, drought, water, temperature) vary by geography, it appears that risk factors for introduction of human pathogens to plants may also vary. • Describing baseline microbiota associated with agricultural commodities in the field is an important step towards improving our understanding of a wide range of important objectives from plant pathology and horticultural sustainability, to food safety. [ABSTRACT FROM AUTHOR]

[Display omitted] • Carotenoid and sugar profiles of melons grown at five locations were reported. • Total sugar content was higher in honeydew HD-150 grown in Georgia. • Tuscan type (DaVinci) grown in Texas had significantly higher β-carotene content. • Three ζ-carotene isomers were identified in cantaloupe cultivars. • Cultivar and location significantly influenced the phytochemical composition. The sensory and functional quality attributes of muskmelons (Cucumis melo L.), such as flavor, sweetness, color, and texture, determine consumer preferences. Genetic makeup primarily regulates these traits, but environmental factors such as soil type, irrigation, and temperature affects yields and quality. Here, we investigated variation in quality traits of diverse melon cultigens (advanced breeding lines or cultigen) grown in multiple locations (California, Texas, Georgia, Arizona, and North Carolina) across the United States. Mesocarp sugar and carotenoid concentrations varied significantly as a function of production location and cultigen. Multivariate analyses revealed significant cultigen, location, and interactive effects on fruit quality. The highest sugar content was found in a honeydew melon cultigen (HD-150; 83.1 ± 2.36 mg/g) grown in Georgia and the Western Shipper type cantaloupe (F-39; 70.8 ± 2.85 mg/g) grown in North Carolina compared to the other cultigens. The Tuscan type (Da Vinci) grown in Texas and Georgia had the highest β-carotene contents (29.1 ± 3.37 and 33.6 ± 1.73 μg/g, respectively) compared to the other cultigens. These findings suggest that cultivar and location significantly influenced melon phytochemical composition, will help melon breeding programs improve the sensory and functional qualities of melons and identify suitable cultivars for specific environments to maximize fruit quality. [ABSTRACT FROM AUTHOR]

Soil amended with biochar has many potential environmental benefits, but its influence on the fate of nitrogen (N) under irrigated conditions is unclear. The objective of this research was to determine the effects of biochar and interactions with irrigation on N movement in soil, gas emissions, and leaching. A three-year study was conducted in an onion field with three main irrigation treatments (50, 75, and 100% of a reference that provided sufficient water for plant growth) and three biochar amendment rates (0 or control, low char - applied first year at 29 Mg ha−1, and high char - added both first and second year for a total 58 Mg ha−1) as sub-treatments in a split-plot design. Nitrogen fertilizer was applied three times during first year growing season, but weekly the second year. Ammonia (NH 3) volatilization, nitrous oxide (N 2 O) emission, and nitrate (NO 3 −) in soil pore water were monitored during growing season, and annual N (total and NO 3 −) changes in soil profile were determined for first two years. Nitrate leaching was measured in the third year. Ammonia volatilization was affected by fertilization frequency with higher loss (5–8% of total applied) when fertilizer was applied in large doses during the first year compared to the second year (4–5%). Nitrous oxide emissions were ≤0.1% of applied N for both years and not affected by any treatments or fertilization frequency. Nitrate concentration in soil profile increased significantly as irrigation level dropped, but most of the NO 3 − was leached by winter rain. There was no significant biochar effect on total N gas emissions or soil NO 3 − accumulation, but significant irrigation effect and interaction with biochar were determined on soil NO 3 − accumulation. High leaching was associated with biochar amendment and higher irrigation level. Irrigation strategies are the key to improving N management and developing the best practices associated with biochar. Unlabelled Image • Biochar increased soil organic carbon, pore water pH, and electrical conductivity. • Biochar had no effect on ammonia emission, nitrous oxide emission and soil nitrate. • Irrigation had a profound impact on soil nitrate accumulation and leaching. • Higher leaching is associated with soil amended with biochar. • Irrigation, not biochar, and their interaction had significant effects on yield. [ABSTRACT FROM AUTHOR]