Fresh-cut lettuce is one of the most commercially important and perishable products in the fresh-cut vegetable industry. Tissue deterioration following processing is driven by a complex interplay of genetic, physiological, and preharvest factors determining both respiration rate and membrane stability. Fifteen accessions of Lactuca sativa were evaluated across 15 independent experiments spanning production environments, leaf developmental stages, storage temperatures, and processing conditions. Nine respirometric parameters were assessed for their capacity to predict electrolyte leakage (electrical conductivity, EC), a measure of membrane deterioration. Across three analytical approaches (Pearson correlation, partial least squares, and random forest), Time Under Hypoxia (TUH) was the strongest predictor of EC, while CO₂ area was the most robust continuous metabolic predictor. A universal critical oxygen threshold of approximately 0.50% O₂ was identified as the anaerobic compensation point, below which both the Gas Stability Index (GSI) and EC diverged sharply from their baselines, independent of cultivar, leaf age, and production environment. Temperature sensitivity (Q10) was similar for O₂ consumption (3.0) and EC (2.9), but EC was disproportionately sensitive to the 2–13 °C shift (Q10 = 4.3 vs. 1.9), underscoring the importance of cold-chain maintenance. A meta-analysis revealed a borderline non-significant correlation between CO₂ area and EC across cultivars (r = 0.489, p = 0.062), with perfect concordance between the favorable qSL4 allele and low deterioration regardless of respiration rate. A 10-day jar assay predicted 37-day MAP performance with high accuracy (r = 0.764, p = 0.0004), validating it as a rapid platform for postharvest screening and breeding.

Salt stress is one of the most important abiotic stresses limiting crop production in the salinity affected growing regions. Lettuce (Lactuca sativa L.) is sensitive to salinity. Understanding the physiological and biochemical mechanisms involved in salt tolerance would facilitate developing strategies to breed lettuce cultivars with improved salt tolerance. Membrane lipid remodeling has been shown to play important roles in adaptation and tolerance to salt stress in several crop species; however, such information is lacking for lettuce. Accordingly, we conducted a controlled growth chamber experiment to investigate membrane lipid remodeling under salt stress using four pairs of lettuce genotypes - each pair consisting of a salt-tolerant and a salt-sensitive genotype from the same horticultural type. Based on the 15 lipid classes analyzed, the lettuce leaf lipidome consisted of 79

This study investigated foliar-applied silicon dioxide (SiO2​), alone and with calcium (Ca), as a sustainable strategy to enhance lettuce quality and performance, using a genetically diverse panel of accessions for broad applicability. We conducted multi-year outdoor pot and field experiments to assess the effects of a range of SiO2​ and Ca concentrations and a promising subset of treatments, respectively. We evaluated key horticultural traits, resistance to diseases, pests, and physiological disorders, as well as post-harvest quality and plant mineral composition. The treatments provided significant benefits for several quality-related traits. A combination of 3.66 mM SiO2 and 2.50 mM Ca significantly improved plant biomass, leaf thickness, and anthocyanin concentration in pot experiments. In field trials, 3.66 mM SiO2​ application delayed bolting, reduced downy mildew severity, and increased leaf thickness, chlorophyll, and anthocyanin content. Notably, the combined SiO2 and Ca spray significantly reduced post-harvest deterioration in both pot and field experiments, demonstrating a synergistic interaction. Analysis of mineral elements revealed that the treatments modified the uptake and correlations among several elements in the plant tissue. Foliar SiO2​ and Ca applications, particularly in combination, represent an effective approach for enhancing key lettuce quality parameters. While no significant yield gains were observed in field trials, the improvements in post-harvest quality, disease resistance, delayed bolting, and plant composition are clear evidence that this strategy can reduce crop losses and improve overall product quality.

Background Contamination of fresh produce with human pathogens remains a serious public health and economic concern due to the absence of effective kill steps in the farm-to-fork chain. Escherichia coli O157:H7 has been implicated in multiple illness outbreaks linked to lettuce.Results We examined the exometabolomic profile of 31 lettuce genotypes and identified variations in the chemical composition of both the leaf surface and the leaf apoplast, supporting variable bacterial growth. Furthermore, inoculation with E. coli O157:H7 induced changes in the overall chemistry of these leaf niches, allowing the identification of many niche-specific differentially accumulated metabolites (DAMs). Intersection analysis revealed little overlap of DAMs among the genotypes, suggesting that multiple metabolites, or a combination of metabolites, may contribute to bacterial persistence in phyllosphere niches. This information guided the design of metabolite cocktails to supplement bacterial inoculations of leaves. Overall, we observed that inhibitory and promoting cocktails significantly shifted the bacterial population titer to lower and higher, respectively, when compared to the control without metabolite supplementation. These shifts were more pronounced in some lettuce genotypes than others.Conclusions These findings provide new insights into how the phyllosphere chemistry influences the survival of E. coli O157:H7, offering potential targets to mitigate food safety concerns through genetic and metabolic engineering.

Tipburn (TB) is a devastating physiological disorder in lettuce (Lactuca sativa) linked to localized calcium (Ca2+) deficiency. While biparental population studies have identified tipburn-linked QTLs, the core genetic mechanisms across diverse germplasm remain poorly understood. We utilized an integrative physiological-genetic framework to dissect TB genetic architecture in a diversity panel of 498 lettuce accessions evaluated over six years. Structural equation and response surface modeling established that TB risk is driven by a supply-demand imbalance regulated by plant biomass (PB) and developmental rate (DS). Although Ca2+ content significantly influenced TB incidence, it did not account for all phenotypic variance, suggesting the existence of Ca2+- independent resistance pathways. To isolate these, we performed GWAS on residual TB that accounted for PB, DS, and bulk Ca content, effectively decoupling plant physiology from resistance. We identified a stable cellular integrity hub on chromosomes 2 (BIN 2.21) and 8 (BIN 8.04), providing resistance regardless of biomass, developmental rate, or bulk Ca2+ status. Conversely, a major locus on chromosome 7 (BIN 7.17) acted as a developmental hub, where resistance is entirely mediated by bolting time and mineral partitioning. Candidate gene analysis at BIN 2.21 identified phosphoinositide phospholipase (PLC) as a putative primary regulator; sequence analysis revealed a highly divergent PLC protein variant strongly associated with the lowest TB incidence. Other candidates include catalases (BIN 8.04) involved in oxidative stress mitigation and myosin-11 motor proteins. Our findings move beyond simple trait associations to identify stable, vigor-independent genetic targets, providing a roadmap for breeding high-yielding, tipburn-resilient lettuce cultivars.

Lettuce is a crucial component of a healthy, well-rounded diet. The annual consumption of leafy vegetables in the U.S. is approximately 6 kg per capita. While most lettuce crops are traditionally grown in open fields, there has been a recent increase in production within controlled environment systems. U.S. lettuce growers are currently facing several challenges, including labor shortages and rising costs, water scarcity, high fertilizer costs, and concerns about food safety. Lettuce production and quality control processes are labor-intensive. Traditionally, the nutrient composition of lettuce has been determined through laboratory tests conducted by trained technicians. However, advancements in technology, such as computer vision and digital imaging, offer the possibility of obtaining real-time data while reducing labor costs. This study utilized hyperspectral image data and artificial neural networks (ANN) to estimate the nutrient composition and quality of lettuce grown in a controlled environment. One challenge in the application of ANN and other machine learning algorithms is selecting the most appropriate features to prevent overfitting in predictive model development. To address this, various feature selection and data size reduction methods were explored. The results of the study indicate that the ANN model accurately classified lettuce contents at a rate of 100

Reusing and recycling treated wastewater is a sustainable approach to meet the growing demand for clean water, ensuring its availability for both current and future generations. Wastewater can be treated in such advanced ways that it can be used for industrial operations, recharging groundwater, irrigation of fields, or even manufacturing drinkable water. This strategy meets growing water demand in water-scarce areas while protecting natural ecosystems. Treated wastewater is both a resource and a challenge. Though it may be nutrient-rich and can increase agricultural output while showing resource reuse and environmental conservation, high treatment costs, public acceptance, and contamination hazards limit its use. Proper treatment can reduce these hazards, safeguarding human health and the environment while enhancing its benefits, including a stable water supply, nutrient-rich irrigation, higher crop yields, economic development, and community resilience. On the one hand, inadequate treatment may lead to soil salinization, environmental degradation, and hazardous foods. Examining the dual benefits and risks of using treated wastewater for agricultural irrigation, this paper investigates the complexities of its use as a valuable resource and as a potential hazard. Modern treatment technologies are needed to address these difficulties and to ensure safe and sustainable use. If properly handled, treated wastewater reuse has enormous potential for reducing water scarcity and expanding sustainable agriculture as well as global food security.

Silicon dioxide (SiO2) foliar application offers a promising strategy for enhancing lettuce (Lactuca sativa L.) resilience under temperature extremes, salinity, and drought stress. This study investigated the effects of SiO2 treatment on three lettuce cultivars exposed to varying temperature, salinity, and drought conditions in a controlled growth chamber environment. Silicon treatment (3.66 mM) significantly enhanced plant biomass under suboptimal (15 °C), optimal (20 °C), and salinity stress conditions. Notably, the SiO2 effect was most positive under severe salinity stress (100 mM NaCl), where its application increased plant weight together with chlorophyll and anthocyanin content. When increasing SiO2 concentrations from 0 to 29.30 mM were tested, optimal results to alleviate severe salinity stress were consistently observed at 3.66 mM, with peak performance in fresh weight, plant diameter, chlorophyll, and anthocyanin content. Higher SiO2 concentrations progressively diminished these beneficial effects, with 29.30 mM treatment leading to reduced growth and increased leaf chlorosis. Comprehensive mineral composition analysis revealed complex interactions between silicon treatment and elemental profiles at 100 mM salinity stress. At 3.66 mM SiO2, plants accumulated the highest levels of both K (20,406 mg/kg dry weight, DW) and Na (16,185 mg/kg DW) while maintaining the highest K/Na ratio (1.26). This suggests that Si enhances cellular ion compartmentalization rather than exclusion mechanisms, allowing plants to manage higher total ion content better while minimizing cytoplasmic damage. Drought stress conditions unexpectedly revealed negative impacts from 3.66 mM SiO2 application, with decreased plant fresh weight at moderate (50% soil water content, SWC) and severe (30% SWC) water limitations, though results were statistically significant only under severe drought stress. The study highlights silicon’s potential as a stress mitigation agent, particularly under salinity stress, while emphasizing the need for concentration-specific and stress-specific approaches. These findings suggest that foliar SiO2 application could be a valuable tool for enhancing lettuce crop productivity under both optimal and challenging environmental conditions, with future research warranting field validation and full market maturity assessments.

Fresh-cut lettuce is widely used in ready-to-eat salads sold in modified atmosphere packages (MAP). Even in MAP, fresh-cut lettuce has short shelf life that results in loss of nutrients. Lettuce cultivars exhibit genetic variation for shelf life in MAP, but their variation for nutrient retention is not known. Fifty accessions were evaluated for initial content of ascorbic acid (AsA), carotenoids, and sugars and their retention in storage. Accessions with high content and/or good retention of one or more nutrients were identified. The romaine accession ‘Floricos’ had high levels of all the three nutrients. Accessions with relatively high retention of all the three nutrients were ‘Salinas 88’, ‘Siskiyou’, ‘Solar’, SM09A, ‘Romance’, and ‘Green Towers’. Romaine cultivars, ‘Balady Barrage’, ‘Green Towers’, and ‘Darkland’ had relatively high initial levels of all tested nutrients and good rate of their retention. There was no clear correlation between initial AsA/carotene concentrations and their retention rates, suggesting that besides content, retention of nutrients should also be a breeding target in a lettuce nutritional improvement program. Statistical analyses with the Pearson’s correlation coefficient determined a negative relationship between tissue deterioration (AUDePS) and retention of all tested nutrients [r of -0.52 (P < 0.0001) for AsA, -0.27 (P < 0.01) for total carotene, and -0.59 (P < 0.0001) for total sugars], suggesting that an increase in tissue deterioration intensifies nutrient decay. Broad-sense heritability (H2) across the experiments was 0.15 for AsA, 0.23 for total carotene, and 0.50 for total sugars. Identification of germplasm with high nutrient content, extended shelf life and good nutrient retention provides valuable information for the lettuce industry and associated breeding programs.

This review describes the taxonomy, phylogeny, and diversity of wild Lactuca spp. and their relationship to cultivated lettuce (Lactuca sativa). The value of the different species as sources of useful variation for a range of economically important traits is detailed and the case is made for the conservation of more accessions in global genebanks. The integration of knowledge from research using the wild and domesticated species is highlighted. Lettuce (Lactuca sativa L.) is an annual species in the family Asteraceae (formerly Compositae). It is a widely cultivated leafy vegetable and one of the oldest domesticated crops. In addition to their high nutritional value, lettuce plants are aesthetically pleasing. A range of lettuce morphotypes has been developed to suit various production systems, meet the demands of the processing industry, and to satisfy consumer demand. Disease- and pest-resistant cultivars are a priority, as pesticide application is often not possible because of potential pesticide-related health risks due to lettuce’s relatively short cultivation period. Wild Lactuca species closely related to lettuce were first utilized in breeding programs in the early twentieth century in USA and later in Europe. They continue to play a vital role in modern breeding as sources of resistance to important diseases and pests, tolerance to abiotic stresses (e.g., salinity, drought, temperature), and sources of variation in leaf taste, structure, and secondary-metabolite composition. The importance of wild Lactuca species in lettuce crop improvement extends beyond the close relatives of the crop. A thorough understanding of the taxonomy and phylogenetic relationships within the genus Lactuca provides insight into the history of domestication of lettuce, the management of genebank collections, and the utilization of germplasm in breeding and genetic studies. This knowledge aids identification and functional analysis of key genes and development of molecular markers for lettuce improvement. Current research supports the classification of L. serriola L. as the direct progenitor of cultivated lettuce, with the Middle East and Egypt identified as two centers of domestication. Lactuca virosa L. and L. saligna L. have also been utilized in lettuce breeding over the past 20–30 years and there has been an increased interest in exploiting other Lactuca species in recent years. Despite their importance, wild Lactuca species remain underrepresented in public-sector genebanks, with only a limited number of accessions available. Challenges, such as incomplete biogeographic and ecological data and frequent miss-identification of accessions, hinder the effective management and use of the collections in breeding programs. Recent studies have advanced our understanding of relationships within the subtribe Lactucinae, but the taxonomy of this lineage remains unresolved. The current taxonomic classification recognizes 73 Lactuca spp.; however, further research is needed to confirm species delineation and refine their classification. This paper proposes two potential approaches to address the unresolved taxonomy of Lactucinae: either recognizing each monophyletic unit as a distinct genus or adopting a broader definition of the genus Lactuca to encompass its diverse lineages.

A large effect and environmentally stable QTL was identified on LG2 that confers high levels of INSV resistance in lettuce cultivar Eruption. Impatiens necrotic spot virus (INSV) has recently emerged as a major threat to lettuce production in the Salinas Valley of California, the region which contributes over 60

The presence of antimicrobial resistance genes (AMRGs) on crops is of concern to public health since plant-derived foods may serve as vectors of AMRGs to human pathogens. This study mined the bacterial metagenomes of soil and lettuce from harvest through processing and storage to characterize their comprehensive resistomes (antibiotics, metals, and biocides). Cold-stored lettuce had the greatest number of AMRG reads per million of all sample types. AMRGs were overall dominated by metal resistance determinants, except those of processed lettuce (cut, washed in chlorinated water, and rinsed), which were heavily enriched in genes encoding biocide resistance. The greatest percentage of drug resistance genes, when averaged over all sample types, belonged to resistance to β-lactams (30 %) followed by aminoglycosides (6.7 %); and specific allele sequences from both classes were observed in common between lettuce and soil sampled next to lettuce heads. Genes for resistance to β-lactams were in highest relative abundance (RA) on cold-stored lettuce and lowest in soil. Several extended-spectrum β-lactamase genes and the colistin resistance gene mcr-9.1 were detected in the cold-stored lettuce resistome. Harvest season and field type had a significant effect on the comprehensive resistome of most sample types (PERMANOVA, P < 0.05). Notably, the RA of β-lactams resistance genes in the drug resistome of cold-stored lettuce represented 17.4 % and 2.0 % in spring vs. fall, and 11.3 % and 3.9 % in the commercial vs. experimental field, respectively. This study highlights the multifactorial role of the biotic and abiotic environment on the comprehensive resistome of lettuce during production and storage.

Bacterial leaf spot (BLS) of lettuce (Lactuca sativa L.) is caused by the bacterium Xanthomonas hortorum pv. vitians that is hypothesized to have at least three races of the pathogen present in North America as defined by their differential resistance phenotypes in lettuce cultivars/accessions. Although resistance to X. hortorum pv. vitians race 1 has been identified in cultivated lettuce, numerous other X. hortorum pv. vitians strains cause disease on cultivars carrying this resistance locus. Thus far, resistance to these "additional" X. hortorum pv. vitians strains has not been adequately described in L. sativa or in any other wild Lactuca species sexually compatible with cultivated lettuce. We have performed an extensive screening of approximately 500 Lactuca accessions from L. sativa, L. serriola, L. saligna, L. virosa, L. aculeata, L. altaica, and L. perennis species to identify accessions resistant to these additional X. hortorum pv. vitians races. Following the initial screenings, greenhouse tests confirmed that X. hortorum pv. vitians race 2 and race 3 could be defined using L. serriola accessions. Race 2 strain BS3127 had an incompatible response (hypersensitive response) on 10 L. serriola accessions, including PI 491114 and PI 491108, whereas race 1 (BS0347) and race 3 (BS2861) strains of X. hortorum pv. vitians showed a compatible response (disease) on these genotypes. L. serriola accession ARM09-161 (and selections derived from it) was the only genotype resistant to the race 3 strain BS2861. L. serriola accessions identified in this study to be resistant to race 2 and race 3 of X. hortorum pv. vitians, together with race 1-resistant cultivars, can be used for pyramiding resistance loci against the three races of the BLS-causing pathogen.

Lettuce (Lactuca spp.) is one of few edible plant species that produce latex. During lettuce harvest, latex leaks from ruptured laticifers onto the cut stem and adheres to other lettuce heads, harvesting tools, and packaging. Little is known about the colonization of lettuce latex by Shiga toxin-producing E. coli O157:H7 (EcO157), the main causal agent of outbreaks linked to lettuce. We screened 14 lettuce genotypes, including wild lettuce and commercial morphological types, for EcO157 multiplication in their latex-coated cut stems. Change in EcO157 density after its inoculation into the latex of these genotypes differed significantly and ranged from a 1.7x decline to a 3.6x increase over 6 h at 25 degrees C. EcO157 density increased in all genotypes except one, a romaine lettuce breeding line that caused decline of the pathogen. Latex biochemical properties, such as concentration of sucrose, glucose, fructose, phenolic compounds and H2O2, and peroxidase (POD) activity, were quantified in all genotypes. These traits varied significantly among genotypes, but only POD activity correlated significantly with the change of EcO157 density in the latex (r =-0.553). Total phenolics and H2O2 concentrations were also negatively and significantly correlated with each other (r =-0.608). The inhibitory effect of POD on EcO157 multiplication in lettuce latex and the identification of a genotype that causes decline of the pathogen in its latex may serve as new phenotypic and genotypic tools to control microbial contamination of lettuce at harvest. Their integration in lettuce breeding programs may enhance the microbial safety of lettuce.

Fresh-cut lettuce (Lactuca sativa) requires modified atmosphere packaging (MAP) with low oxygen (< 3 % O-2) to prevent enzymatic discoloration. However, some accessions exhibit rapid deterioration under these low oxygen conditions, resulting in significant product loss. This study investigated the mechanisms of this heritable deterioration, linked to the qSL4 locus, by examining respiration and transcriptomic responses. We found that rapid deterioration is associated with continued respiration under very low oxygen levels (<1 % O-2), with minimal effects from CO2 and ethylene. Deterioration differences lessened at higher O-2 levels (similar to 20 %), emphasizing oxygen's critical role. RNA-seq analysis of slow (Salinas 88) and rapid (La Brillante) deteriorating cultivars revealed distinct early transcriptomic shifts under MAP. La Brillante upregulated more genes (1837) and downregulated fewer (1735) than Salinas 88 (1185 upregulated, 2367 downregulated), indicating higher metabolic activity in rapid deteriorating cultivar. Notably, glycolysis and electron transport chain (ETC) genes showed differential expression; ATP-consuming enzymes (fructokinase, hexokinase) and ETC complexes I and IV were upregulated in La Brillante but downregulated in Salinas 88. Conversely, Salinas 88 exhibited higher expression of alternative oxidase (AOX) genes, suggesting ATP conservation and reduced oxygen use. These findings indicate that slow-deteriorating genotypes maintain quality under low oxygen by limiting sugar and ATP consumption, while rapid deteriorating genotypes sustain higher metabolic activity, accelerating deterioration and likely shifting towards fermentation. This study provides insight into the early stages of lettuce deterioration and highlight the importance of low oxygen tolerance and metabolic adjustment capacity, setting the stage for future genomic research and functional studies on postharvest respiration and fermentation.

Lettuce (Lactuca sativa) is highly vulnerable to Sclerotinia minor, the pathogen causing lettuce drop. Breeding for resistance is the most effective control strategy; however, full resistance has not been achieved, and current partial resistance sources are often linked with undesirable traits, such as early bolting. This study aimed to unravel the genetic basis of partial resistance to S. minor and its relationship with plant maturity (bolting), stem mechanical strength (SMS), and cell wall composition (CWC) using a recombinant inbred line (RIL) population derived from a cross between the susceptible iceberg cv. 'Salinas' and the resistant oil-seed accession PI 251246. Field evaluations indicated that resistance was linked to earlier bolting, stronger stems, and higher pentose content. Path analysis demonstrated that earlier-maturing plants exhibited increased resistance through enhanced SMS and modified CWC, particularly with higher xylose and lower arabinose levels. Further analysis indicated a significant relationship between syringyl lignin content and resistance, especially in plants with varying bolting responses. Three key quantitative trait loci (QTLs) on linkage groups (LG) 2, 6, and 7 were consistently associated with resistance, bolting, and SMS. Importantly, residual QTL analysis revealed that the resistance locus on LG7 acted independently of maturity, suggesting a distinct resistance mechanism. Callose synthase emerged as a key candidate gene within the LG7 resistance QTL, located near - but distinct from - genes associated with plant maturity and flowering. These findings provide valuable insights into decoupling resistance from early bolting, suggesting a pathway for breeding lettuce cultivars with improved disease resistance and delayed bolting.

Foodborne illness linked to fruit and vegetables poses a major challenge to public health and horticulture production. Processed lettuce has been implicated in recurrent outbreaks of pathogenic Shiga toxin-producing Escherichia coli (STEC) infection. We hypothesized that plant defenses elicited by mechanical injury may effect STEC inhibition in cut leaves. Intact and cut leaves of 31 lettuce cultivars (Lactuca spp.) selected from >500 accessions based on their resistance to common insect pests and the necrotrophic lettuce drop pathogen were assessed for STEC serovar O157:H7 (EcO157) survival under cold storage conditions. The cultivars were previously ranked also for phenotypes such as resistance to other phytopathogens and physiological traits. Total leaf phenolic compounds, anthocyanins, and reactive oxygen species (ROS); and phenylalanine lyase (PAL), peroxidase (POD), and polyphenol oxidase (PPO) activity were quantified in each cultivar. Principal Component Analysis (PCA) and K-means cluster analysis were applied to group phenotypes and EcO157 population decline on lettuce. In five cultivars, high resistance to herbivorous insects (aphids, leaf miners and thrips), diseases (lettuce drop, downy mildew, and Impatiens Necrotic Spot Virus), and the disorder tipburn was associated with up to 42-fold EcO157 population decline on cold-stored cut (shredded) leaves, and with up to 11-fold difference in decline on cold-stored intact vs cut leaves (Delta D). The decline on these cold-stored cut cultivars also was up to 24-fold greater than on the cultivar with the lowest decline, and up to 8-fold greater than the mean decline for all 31 cultivars (P < 0.01). Resistance to the hemibiotrophic pathogen causing lettuce bacterial leaf spot, Xanthomonas hortorum pv. vitians, was not indicative of high EcO157 inhibition in this system. High PAL activity, and phenolic and anthocyanin content (PPA); and high PAL and POD activity, were associated with high EcO157 population decline (P < 0.05). One cultivar with high susceptibility to herbivorous insects and phytopathogens, and low levels of defense metabolism nevertheless showed high EcO157 inhibition, suggesting other plant inhibitory characteristics at play. Basal plant immunity and pathways associated with a strong wound response may inform about enteric pathogen survival on minimally processed postharvest lettuce. The related traits identified in this study may serve to breed new genotypes with intrinsically enhanced microbial safety.

BackgroundSclerotinia spp. are generalist fungal pathogens, infecting over 700 plant hosts worldwide, including major crops. While host resistance is the most sustainable and cost-effective method for disease management, complete resistance to Sclerotinia diseases is rare. We recently identified soft basal stem as a potential susceptibility factor to Sclerotinia minor infection in lettuce (Lactuca sativa) under greenhouse conditions. ResultsAnalysis of stem and root cell wall composition in five L. sativa and one L. serriola accessions with varying growth habits and S. minor resistance levels revealed strong association between hemicellulose constituents, lignin polymers, disease phenotypes, and basal stem mechanical strength. Accessions resistant to basal stem degradation consistently exhibited higher levels of syringyl, guaiacyl, and xylose, but lower levels of fucose in stems. These findings suggest that stem cell wall polymers recalcitrant to breakdown by lignocellulolytic enzymes may contribute to stem strength-mediated resistance against S. minor. ConclusionsThe lignin content, particularly guaiacyl and syringyl, along with xylose could potentially serve as biomarkers for identifying more resistant lettuce accessions and breeding lines. Basal stem degradation by S. minor was influenced by localized microenvironment conditions around the stem base of the plants.

Pea (Pisum sativum) dominant for the fundamental color gene A showed a high level of resistance to Globisporangium ultimum (formerly Pythium ultimum) seed rot. Reciprocal crosses demonstrated that, with our materials, such resistance was associated with the testa (seedcoat) phenotype but not the embryo phenotype. Dominance of A over a was complete for this trait. Neither wrinkled seed form (r) nor green cotyledons (i) diminished resistance when A was dominant, although both recessive alleles diminished resistance when seeds were borne on white-flowering (a) plants. The product of the A gene functions in the pathway leading to flavonoids, including proanthocyanidins (PAs) and anthocyanidins. We found that resistance to G. ultimum seed rot was closely associated with not only dominant A but also testa PAs and testa sclerenchyma. Even A testas that lacked anthocyanins but contained PAs and sclerenchyma showed a high level of seed rot resistance. Moreover, a mutation removing PAs and sclerenchyma in a narrow zone from the hilum to the radicle markedly increased susceptibility. The PAs in pea testas were predominantly prodelphinidins in seeds from purple-flowered plants (A B) and procyanidins from pink-flowered plants (A b). Compared with procyanidins, prodelphinidins have higher antioxidant activity but are more likely to sequester iron, a particular concern with dry pea. Although A B testas were more resistant than A b to seed rot, the difference seemed too slight to militate against growing pink-flowered pea. We stressed the need for more histological comparisons of A B and A b testas, and we indicated that genes and their phenotypic effects examined during the current study could be useful for modeling biosynthesis of PAs and related cell walls.