ASHS 2025 Conference

Watermelon, Citrullus lanatus, is an important vegetable crop in the United States of which the annual watermelon crop value exceeded $534 million in 2021. In recent years, production has been disrupted by the rapid spread of a serious plant pathogen, Phytophthora capsici. The closest ancestors of today’s domesticated watermelon are thought to be Citrullus mucosospermus and Citrullus amarus, several accessions of which have known resistance to Phytophthora capsici fruit rot, but are untested in regards to stem and root rot. Popular commercially available cultivars, such as ‘All Sweet’, ‘Laelanau’, ‘Penghu’, and ‘Sunshade’, as well as Texas A

Fusarium wilt, caused by the fungal pathogen Fusarium oxysporum f.sp. lycopersici (Fol), threatens tomato crops globally. Fol causes substantial yield losses in susceptible plants and is persistent once established in fields, making gene-based resistance a high-priority for growers. Historically, Fol strains isolated in the Midwest United States have been predominantly race 1, and I-based resistance has been widely deployed and effective. However, there have been increasing numbers of samples sent to diagnostic clinics in the Midwest with Fusarium wilt symptoms, suggesting a potential shift in Fol race prevalence and the need to deploy additional resistances. The aim of our project is to introgress the I3 resistance gene, effective against race 3 Fol, into Midwest-suited processing tomato lines. I3 was originally identified in Solanum pennellii, a wild relative of cultivated tomato (Solanum lycopersicum), and a minimal introgression which reduced linkage drag was developed and introduced into Fresh-Market tomatoes by the University of Florida. We developed backcross families with the I3 gene using the Florida minimal introgression and recurrent parents from the Ohio processing tomato breeding program. Lines were selected for advancement based on I3 genotyping, background genome selection using unlinked single nucleotide polymorphisms (SNPs), and phenotyping of relevant yield and quality characteristics. Our analysis found no significant differences in yield and quality traits between the backcross selections and their recurrent parents, indicating the rapid conversion of parents through this strategy. We are currently combining the I3 and I2 resistance genes through further crossing and will ultimately develop high-performing processing tomato lines suited to Midwest growing conditions that are resistant to all three Fol races.

Understanding germplasm diversity is essential in pepper (Capsicum annuum L.) breeding to enhance disease resistance and fruit quality. This study evaluated morpho-phenological characteristics of UGA-CAPSI-CORE, a collection of 352 globally sourced germplasm classified into six varietal groups (VGs): banana, bell, Italian frier, mini bell, mini sweet, and specialty peppers evaluated in two replications during summer 2024. A total of 12 traits, including eight quantitative (e.g., germination, plant vigor, plant height) and four qualitative traits (e.g., growth habit, fruit position, fruit color), were assessed. Significant phenotypic variation was observed across varietal groups. Germination rates averaged 64%, with mini sweet peppers exhibiting highest germination (71.63%) and least in banana peppers (57.30%). Flowering time slightly varied (87–103 days), with banana peppers flowered late (89.3 days) than Italian frier (88.5 days). Specialty peppers were longer (41.49 cm) while bell types shorter (34.22 cm). Banana peppers and bell types exhibited taller (17.55 cm) and shorter (14.98 cm) stems, respectively. Lodging susceptibility was highest in Italian frier (29.12%) and lowest in mini bell (19.78%). Days to maturity was consistent, with mini sweet accessions requiring slightly longer time (142.51 days) than Banana peppers (141.34 days). Fruit morphology varied significantly, with bell peppers producing the highest lobe count (3.38) and banana peppers having single-lobed fruits. ANOVA confirmed significant variation (p < 0.001) in key traits, and cluster analysis identified six distinct clusters. This study elucidates the genetic diversity within the evaluated germplasm, providing valuable insights for breeding program to focus on enhancing productivity, adaptability, and fruit quality.

Phytophthora capsici is a devastating pathogen in peppers (Capsicum annuum L.), responsible for root, stem, and fruit rot, often leading to yield losses of 40% to 60% in outbreak conditions. Marker-assisted selection (MAS) offers a precise strategy for accelerating resistance breeding. While high-throughput genotyping approaches such as genome-wide resequencing (WGRS) are increasingly adopted, SSR markers remain a practical and informative tool for initial diversity assessment, especially in large and diverse germplasm collections. In this study, 485 globally sourced pepper accessions including 473 accessions from C. annuum and 12 accessions from seven wild Capsicum species were evaluated using 31 SSR markers previously reported to be linked with Phytophthora resistance. Eighteen markers showing robust and reproducible amplification were selected for full-panel genotyping. To ensure consistent and accurate allele calling, SSR allele binning was performed using TANDEM software. The resulting dataset revealed substantial allelic richness, reflecting the broad genetic diversity of the collection. Gradient PCR was also performed to optimize amplification of the 13 initially non-amplifying markers, resulting in six additional markers now suitable for further screening. Downstream diversity analyses, including PCA, STRUCTURE, and phylogenetic clustering, are currently in progress. Additionally, WGRS is planned for this germplasm panel, and integration of SSR and SNP datasets will allow for a comprehensive assessment of genetic relationships, population structure, and resistance allele distribution. Together, these efforts will support the identification of novel resistance sources and inform strategic breeding for improved Phytophthora resistance in pepper.

Seed increase is an essential step in germplasm management, enabling the effective use of genetic resources in breeding, evaluation, and conservation. This study focused on multiplying seed stocks and assessing phenotypic diversity in a globally sourced collection of 485 Capsicum accessions. The collection comprises accessions belonging different species of Capsicum including C. annuum (473), C. chinense (4), C. baccatum (3), C. chacoense (1), C. flexuosum (1), C. frutescens (1), C. galapagoense (1), and C. rhomboideum (1). Evaluated accessions were obtained from diverse genebanks (domestic and international), and collaborative breeding programs that comprises landraces, heirlooms, breeding lines, and exPVPs. To ensure sufficient seed availability, 352 accessions were grown in a greenhouse during summer 2024 and an additional 133 accessions were grown during winter 2024. Simultaneously, twelve agronomic and morphological traits, six pre-harvest (e.g., germination rate, plant vigor, internode number and length) and six post-harvest (e.g., fruit size, pericarp thickness, yield) were recorded. Significant phenotypic variation was observed across varietal groups. Bell and mini bell peppers showed high germination rates (>65%) and marketable yields, with bell types producing the heaviest fruits (79.8 g) and thickest pericarps (5.2 mm). Banana peppers exhibited the longest fruits (13.8 cm) and high plant vigor, while mini bells were completely resistant to lodging. These findings highlight both successful seed multiplication and the phenotypic richness of the collection, offering a valuable resource for pre-breeding, core collection development, and trait-specific selection.

Spinach (Spinacia oleracea L.) produces two types of seeds: spiny and spineless. Seed spine is one of the most important agronomic traits that affect seed treatment, mechanized harvesting and planting, and sowing. This study aimed to identify single nucleotide polymorphism (SNP) markers associated with seed spines in spinach through a genome-wide association study (GWAS), with the goal of developing SNP markers for marker-assisted selection (MAS). GWAS was conducted for the seed spine trait in a panel of 307 diverse spinach accessions using 147,977 SNPs generated from whole genome resequencing. Using MLM, FarmCPU, and BLINK models in GAPIT 3 and TASSEL 5, two significant SNPs associated with seed spines: SOVchr3_141167900, and SOVchr3_141168649 were identified on the chromosome 3. (LOD) values of t-test analysis identified homozygous alleles associated with the spiny and spineless traits in each of the two SNP markers, with LOD values greater than 80.00, and 80.00, respectively. The gene SOV3g042220, located between 141,172,904 bp and 141,183,504 bp on chromosome 3, is proposed as a potential candidate gene associated with the seed spine trait. This research provides valuable insights for MAS in spinach breeding, facilitating the development of spinach lines with desirable seed characteristics.

Vitamin C (VC), also known as ascorbic acid and ascorbate, is a water-soluble antioxidant in plants that promotes skin health and immune function in humans. Spinach (Spinacia oleracea L.), a leafy green vegetable widely valued for its health benefits, has been identified as a target for nutritional enhancement, including increased VC content. However, the complex inheritance of VC necessitates advanced selection methods to accelerate cultivar development. In this study, VC- associated single nucleotide polymorphism (SNP) markers identified through genome-wide association (GWAS) were employed for genomic prediction (GP) to estimate prediction accuracy (PA) for VC content in spinach. A dataset of 147,977 SNPs generated from whole genome resequencing was analyzed in a panel of 347 spinach genotypes using six GWAS models. Sixty-two SNP markers, distributed across six spinach chromosomes, were significantly associated with VC content. PA was assessed using randomly selected SNP sets and GWAS-derived SNP marker sets across various GP models. Results demonstrated that PA exceeded 40% when using 1,000 or more SNPs. Furthermore, incorporating GWAS-derived SNP markers improved PA, achieving a r-value greater 0.70 through Bayes ridge regression (BRR) model. This study highlights the potential of GWAS-derived SNP markers for marker-assisted selection (MAS) and genomic selection (GS) in spinach breeding programs aimed at enhancing VC content. Keywords: Genomic Selection, Genome-Wide Association Study, Spinach, SNP, Prediction Accuracy

Leaf base color in spinach (Spinacia oleracea L.) exhibits substantial phenotypic variation, potentially influencing consumer preference and nutritional content. To elucidate the genetic basis of this variation, we conducted a genome-wide association study (GWAS) utilizing a diverse panel of 313 USDA-GRIN accessions of spinach. This population, characterized by a predominance of white (65%) and red (35%) leaf base colors, was genotyped using whole-genome resequencing (WGR) resulting in the identification of 83,261 high-quality single nucleotide polymorphisms (SNPs) after rigorous filtering. Genetic diversity analyses and association mapping were performed using multiple statistical models, including mixed linear model (MLM), generalized linear model (GLM), BLINK, and FarmCPU, implemented in GAPIT 3, TASSEL 5, and rMVP software. The GWAS identified three significantly associated SNPs (SOVchr3_140405053, SOVchr3_140405474, SOVchr3_140412359) located on chromosome 03, which collectively contribute to leaf base color variation. Within a 50kb flanking region of these SNPs, we identified three candidate genes: SOV3g042000 (membrane protein), SOV3g041980 (mariner transposase), SOV3g041990 (pentatricopeptide repeat). These genetic loci explained 30.55% of the phenotypic variation observed in leaf base color. These findings provide critical insights into genetic architecture governing leaf base color in spinach. The identified SNPs and candidate genes represent valuable targets for marker-assisted selection and gene editing, facilitating the development of improved spinach cultivars with desired leaf base color. Overall, this study contributes to a comprehensive understanding of the genetic control of leaf pigmentation, ultimately supporting targeted breeding strategies for spinach varieties.

Spinach (Spinacia oleracea L.) is a globally valued vegetable, renowned for its rich nutritional content and health-enhancing benefits. Leaf texture, ranging from smooth to savoy, is an important trait influencing consumer preference, taste, and nutritional compositions. This study aimed to conduct a comprehensive genome-wide association study (GWAS) to identify single nucleotide polymorphism (SNP) markers associated with leaf texture in spinach, along with genomic prediction (GP) to facilitate trait screening in breeding programs. GWAS was performed on a panel of 103 USDA spinach germplasm accessions using 12,744 high-quality filtered SNPs obtained from whole-genome resequencing. Several statistical models, including MLMM, MLM, FarmCPU, and BLINK, were applied using the GAPIT 3 tool. Two significant quantitative trait locus (QTL) regions were identified on chromosome 1, spanning from 13,798,232 bp to 51,588,552 bp. Within this region, three SNP markers—SOVchr1_13798232 (LOD 5.84), SOVchr1_51500008 (LOD 9.73), and SOVchr1_51588552 (LOD 5.77) and—showed strong associations with leaf texture. Additionally, another SNP marker, SOVchr2_8225269, on chromosome 2, also exhibited a strong association with this trait. Furthermore, the gene SOV1g002810, located between 13,795,625 bp and 13,803,405 bp on chromosome 1, encodes a ULP_PROTEASE domain-containing protein and is proposed as a potential candidate associated with the trait. GP revealed strong predictive accuracy (PA), with an r value of 0.43. The identified SNP markers and PA metrics provide valuable tools for breeders to spinach breeding programs through marker-assisted selection (MAS) and genomic selection (GS), thereby accelerating the development of spinach lines with desired leaf textures.

Soil salinity is a critical abiotic stress that severely limits spinach (Spinacia oleracea L.) growth and productivity, particularly in salt-affected agricultural regions. Developing salt-tolerant cultivars and identifying genetically diverse germplasm are essential strategies to improve spinach resilience under saline conditions. In this study, 150 spinach accessions from the United States Department of Agriculture (USDA) germplasm collection are evaluated under control and salt stress (300 mM NaCl) conditions in a controlled greenhouse environment. The experiment was conducted using a randomized complete block design with three replications. Seedlings were assessed for chlorophyll content (SPAD value), leaf injury score (1–7 scale; 1 representing no visible injury and 7 representing completely necrotic leaves), and seedling height (cm). Substantial genetic variation was observed among the accessions. Five accessions were identified as salt-tolerant based on trait performance, including higher chlorophyll content, lower leaf injury scores, and greater seedling height under salt stress. These included CPPSIH 3 04, PI 171860, PI 177082, PI 171859, and PI 174387. Broad-sense heritability was high for chlorophyll content, leaf injury score, and seedling height, indicating that these traits are largely controlled by genetic factors under salinity stress. A negative correlation was detected between chlorophyll content and leaf injury score, suggesting that accessions maintaining higher chlorophyll content tended to exhibit less foliar damage under salt stress. These findings highlight valuable genetic resources for spinach breeding programs focused on improving salinity tolerance. Future studies will expand the evaluation to a broader collection of spinach accessions and implement genome-wide association studies (GWAS) to identify single nucleotide polymorphism (SNP) markers that can facilitate molecular breeding for salt tolerance.

Sweet potato (SP) is a staple in many countries, primarily used for human consumption, but also showing potential for animal feed, ethanol production, ornamental use, and industrial applications. SP is mistakenly considered tolerant to drought, but water shortage can significantly compromise the yield and quality of this crop. It is frequently cropped in drought-prone environments, characterized by sandy soil and high temperatures. Identifying drought-tolerant genotypes is essential for the development of future-ready cultivars. This study aimed to evaluate physiological, biochemical, and morphological responses of sweet potato genotypes to water deficit conditions. A completely randomized experimental design was adopted in a 2 x 20 factorial scheme with four replicates. The first factor consisted of two water regimes, 20 and 100% of pot capacity. The second factor included 20 genotypes. Plants were grown in 12L-pots filled with a 2:1 soil-to-sand mixture. All plants were irrigated at full pot capacity for five weeks to ensure establishment. Subsequently, water regimes were imposed employing time-domain reflectometry (TDR) sensors, and evaluations were conducted four weeks later. Parameters assessed included chlorophyll fluorescence, biomass, water potential, gas exchange, biochemical parameters, and secondary metabolites. Genotypes responded differently to water regimes, revealing considerable genetic variability for drought tolerance. Water deficit negatively affected the performance of several genotypes, particularly in relation to the variation of minimum fluorescence (Fv/F0), leaf water potential, and electron transport rate. Correlation analysis showed strong associations among traits of stressed plants. There was a high positive correlation between leaf water potential and fresh mass of the aerial part, as well as the photosynthetic rate with the chlorophyll fluorescence parameters Fm and Fv/F0. Genotypes ‘Luiza’, ‘Canadense’, ‘CIP-420717', ‘Maria Isabel’, and ‘CIP-440186' exhibited superior performance under drought conditions and are promising candidates for breeding programs targeting drought tolerance.

In Florida, lettuce is cultivated in the southern region in wintertime, a period marked by environmental fluctuations. The dominant Histosols in this area are prone to subsidence and exhibit an increased pH due to the incorporation of calcium carbonate, leading to a reduction in phosphorus (P) availability. In the northern part of Florida, lettuce has the potential to be cultivated in sandy soil to supply the high demand of lettuce, however this type of soils naturally exhibits low P availability. To sustainably produce lettuce in these soils, P efficient cultivars should be bred. Prior, lettuce genotypes were identified as P-efficient and P-inefficient across types. The objective of this study was to determine the influence of Genotype × Environment (G×E) interaction on lettuce cultivated under low P inputs. A multi-environment trial was conducted using 22 P-efficient or P-inefficient genotypes in eight experiments distributed across the lettuce season (Fall, Winter, and Spring) at two locations and distributed in a randomized complete block design with four replicates. Five experiments were conducted in histosol soils, and three in sandy soils. Each experiment was cultivated under a standard and a reduced P fertilizer rate . Data collected included head weight, and marketability. The analysis of the G×E for these traits under low P conditions utilized three methodologies: the Finlay-Wilkinson approach, that determines the stability of each genotype across environments independently; the Genotype Genotype × Environment biplots, that discerns the 'which-won-where' patterns for mega-environments and identifies the most stable genotype(s) across environments; and the Bayesian AMMI, that aims to understand genotype stability across environmental factors. The results demonstrated that both crossover and non-crossover G×E interactions are statistically significant, accounting for 16% of the variance for season and for soil types in head weight. These interactions explained 27% of the variance for marketability for P fertilizer treatments, accounting 15% and 9% for season and soil types, respectively. The romaine breeding line 60183 and cultivar Tall Guzmaine were identified as P-efficient, exhibiting non-crossover interaction and stability across P rates, seasons, and soil types. Iceberg cultivars Honcho II, and Cibola, and the loose-leaf RSX743 were P-efficient and exhibited crossover interactions. The analysis revealed that winter planting in both soil types is the most stable and productive environment, with histosol soils achieving higher yields under low P input. Results of this study highlight the importance of G×E interactions to be considered when breeding lettuce cultivars for low P inputs.

Bacterial leaf spot (BLS) of lettuce, caused by Xanthomonas hortorum pv. vitians (Xhv), is a major disease limiting lettuce production worldwide, particularly in tropical environments such as the Everglades Agricultural Area (EAA) in Florida. The pathogen is highly aggressive, rapidly dispersing under favorable conditions, and its sporadic outbreaks make disease prediction and management challenging. While Xhv is primarily known to infect lettuce (Lactuca sativa L.), its potential to colonize alternative hosts, including crops and weeds in lettuce-growing regions, remains poorly understood. This study aimed to evaluate the host range and epiphytic capabilities of Xhv by inoculating two isolates (‘L7’ and ‘SC8B’) onto common leafy vegetable crops and weeds frequently found in or around lettuce fields. A total of 26 plant species were tested, including weeds from Malvaceae (n=1), Portulacaceae (n=1), Amaranthaceae (n=2), Asteraceae (n=3), Brassicaceae (n=1), and Poaceae (n=1), along with vegetable crops from Asteraceae (n=6), Brassicaceae (n=7), and Apiaceae (n=5). Disease severity was assessed 12 days post-inoculation (DPI) using a 0–5 rating scale based on symptomatic foliage area. Initial water-soaked lesions were observed on susceptible lettuce (‘Okeechobee’) at 2 DPI, progressing to necrotic lesions and severe infection with an average disease severity score of 4 at 12 DPI. Notably, symptomatic responses were also observed in endive (Cichorium endivia L.), escarole (C. endivia var. latifolium), and coriander (Coriandrum sativum L.), with median disease severity scores of 3, 3, and 2, respectively. Symptoms in these crops were consistent with BLS in lettuce, including water soaking, chlorosis, and necrosis. In contrast, Brassicaceae species and all tested weeds remained asymptomatic. Bacterial isolations from symptomatic and asymptomatic leaves revealed colonies morphologically consistent with Xhv, displaying yellow pigmentation on nutrient agar. To confirm pathogenicity, hypersensitivity and compatibility response assays were conducted by infiltrating recovered bacterial isolates into resistant (‘PI 358001-1') and susceptible (‘Okeechobee’) lettuce cultivars. Typical disease symptoms developed on susceptible lettuce, confirming Koch’s postulates. The asymptomatic nature of weed species suggests they may serve as reservoirs, potentially contributing to pathogen persistence and dissemination in lettuce fields. These findings provide new insights into Xhv epidemiology and highlight alternative host species that may play a role in disease outbreaks. Understanding the pathogen’s ecological interactions is critical for developing effective disease management strategies and mitigating economic losses in lettuce production systems.