ASHS 2025 Conference

Salix pellita (satiny willow) is a state-threatened shrub willow species which is native to Minnesota and offers appealing ornamental traits. The natural distribution of this taxon in Minnesota is limited primarily by habitat loss. Because the disjunct populations of this species in Minnesota are in decline and because no prior efforts have been made to conserve this taxon, horticultural practices and cultivation could offer a preservation outlet for satiny willow. Prior to this project, Salix pellita was not represented in any germplasm repository in the United States. This study uses GBS (genotyping by sequencing) to characterize diversity among, between, and within wild collected Salix pellita populations from Minnesota, Michigan, and New Hampshire. Diversity metrics Fis, Fst , pairwise Fst and He were used to categorize genetic diversity. High Fis was found within most populations, which can be attributed to population isolation and small population size. Pairwise Fst between state populations (MN-MI, MN-NH, MI-NH) showed high levels of genetic differentiation, which can be attributed to the lack of gene flow between these populations. Ultimately, these metrics will be used to establish a genetically diverse ex situ collection of Salix pellita.

Phytophthora capsici is one of the top ten oomycete plant pathogens infecting a wide range of economically important crops. P. capsici was first reported to infect chile pepper (Capsicum annuum L.) in New Mexico Agricultural Research Station in Las Cruces, NM, and is currently a major threat on chile pepper production worldwide. The pathogen affects multiple plant parts at all stages of growth leading to death and significant economic losses. The diseases caused by P. capsici are difficult to eliminate which can be attributed to its broad host range, complexity of the inheritance of disease resistance, its global distribution, and diversity of the pathogen population. This study aims to analyse global distribution and diversity of P. capsici isolates infecting different hosts including Cucumis sativus, Cucurbita pepo, Capsicum annuum, Cucurbita maxima, Piper nigrum, Solanum lycopersicum, and Theobroma cacao by examining mitochondrial genes (secY, cox2, nad9, rps10) using Clustal Omega. Phylogenetic analyses based on different mitochondrial genes revealed diversity of P. capsici isolates. Based on secY, cox2, and nad9 genes, clustering patterns are found based on both the host from which they were isolated from and their geographical origin, while for rps10 gene, most of the isolates are found in one cluster. Notably, a separate analysis focusing on P. capsici isolates collected from C. annuum showed five isolates from South Korea (P15103, P1514, P15157, P15160, and P15161) clustered together, as did three isolates from New Mexico (P10199, P1091, and P3605). Similarly, isolates P10736 and P3941 from China, along with P15155 and P6741 from South Korea, consistently clustered together across all four genes analyzed. Future genetic diversity studies will include analysing the pangenome of P. capsici isolates from Texas, Florida, Arizona, Illinois, New Jersey, and New Mexico, USA; and screening of C. annuum recombinant inbred lines using different isolates with varying levels of virulence. Understanding genetic makeup of isolates may provide insights of their pathogenicity. Meanwhile, the results of screening of C. annuum recombinant inbred lines will aid in understanding the inheritance of disease resistance. Altogether, these approaches can contribute to the development of more effective and sustainable disease management strategies against P. capsici.

Bigleaf hydrangea (Hydrangea macrophylla) is an economically important ornamental shrub produced worldwide for the floral trade, as a container crop, and as a landscape plant. Powdery mildew (PM), caused by Golovinomyces orontii, is a widespread disease of bigleaf hydrangea impacting production and salability of plants. However, mechanisms of resistance to PM of bigleaf hydrangea are still largely unexplored. The purpose of this study was to investigate whole-plant response to PM infection and identify differentially expressed genes (DEGs) that contribute to the PM disease response in bigleaf hydrangea. Mature plants of four cultivars (‘Blushing Bride’, ‘Endless Summer’, ‘Nigra’, and ‘Veitchii’) were chosen based on their variable responses to natural PM infection. Powdery mildew was collected by harvesting naturally infected leaves from field plants and applied via spray inoculation averaging ~20ml per plant, with inoculum rate being 1 x 104 CFUmL-1, to six replicate plants per cultivar; one plant per cultivar was sprayed with water as a control. Whole plant response (% of plant tissue infected) was measured visually on a scale of 0-100% disease severity weekly starting from 29 Nov 2023 to 14 Feb 2024 and used to calculate Area Under the Disease Progress Curve (AUDPC). Plant tissue was sampled at 12 different time points, from 1 hour after inoculation (HAI) to 5 days after inoculation (DAI) using a leaf disc puncher and immediately flash frozen in liquid nitrogen. RNA was extracted using a Qiagen RNeasy Plant Mini kit and sequenced using NovaSeq. Adapters were removed from raw reads using fastp (0.23.4) and trimmed reads were aligned to the ‘Endless Summer’ reference genome using STAR (2.7.11b). STAR bam files were sorted with samtools (1.21) and featurecounts (2.0.6) was used for the gene model counting. DESeq was used to identify DEGs between ‘Veitchii’ and ‘Nigra’. There were significant differences among cultivars for AUDPC, with disease severity ranging between 7.7 and 19.2%. Bigleaf hydrangea ‘Nigra’ and ‘Endless Summer’ were the most susceptible to PM infection and ‘Veitchii’ the most tolerant. There were 11,629 DEGs total with 6,145 upregulated compared to ‘Veitchii’ and 5,484 downregulated compared to ‘Nigra’. DEGs were sorted by their P-adjust value followed by the Log 2-fold change. Many of the top 25 strongest DEGs include genes for plant stress such as serine threonine-protein kinase, PAN_AP, and leucine-rich repeat family proteins. These genes are currently being tested for expression levels among bigleaf hydrangea cultivars.

Tomato is one of the economically important agricultural crops worldwide. Approximately 80% of tomatoes are consumed fresh, while 20% are used in various processed food products. The tomato production in the United States (US) contribute and $2.8 billion to the national economy annually. However, virus infections are a major threat to tomato production and fruit quality. Tomato brown rugose fruit virus (ToBRFV) which was reported in 2014 and has spread in more than 50 countries since then, is a highly infectious and stable Tobamovirus spreads mechanically and can stay on a surface for weeks. Its ability to overcome existing resistance genes in tomato is the main concern, emphasizing the urgent need to identify tolerance or resistance in tomatoes cultivars. Besides this, horse nettle virus A (HNVA), recently reported to infect tomatoes in Oklahoma was previously limited to a weed named horse nettle (Solanum carolinense), and exhibits a concerning host shift, causing symptoms such as curling, cupping, and brown discoloration of leaves in tomatoes plants. The objective of this study was to evaluate commercially cultivated tomato cultivars in the US for resistance against both ToBRFV and HNVA. The tomato seedlings were inoculated mechanically with ToBRFV and HNVA and were observed and scored weekly at 7-, 14-, 21-, and 28-days post-inoculation (dpi) on a severity scale of 0 to 3 where 0,1, 2, and 3 correspond to no symptoms, mild, mildly severe and severe symptoms respectively. At 28 dpi, representative plants were tested using virus-specific RT-PCR assays to confirm systemic infection. The findings suggest that there are no resistant cultivars against ToBRFV while there are some showing tolerance based on the symptom severity scores. For HNVA, 22 cultivars have been screened so far and were mostly tolerant but not resistant. These results provide insights into the interaction of these emerging viruses with widely grown tomato cultivars and help us to identify tolerant cultivars to inform the growers and the variation in disease severity which would be valuable for breeders to guide future breeding strategies aimed at ToBRFV and HNVA resistance.

Focus on the role of National Clean Plant Networks and other agencies (potentially including private parties), and discuss best practices.

Jerusalem artichoke (Helianthus tuberosus L.) (sunchoke) presents a resilient and low-input crop alternative with potential for both biomass and tuber production. However, a comprehensive understanding of varietal performance in specific environments like Ohio is essential to unlock its full agricultural potential. This study evaluated the growth and yield performance of five Sunchoke varieties (Beaver Valley, Dwarf Sunray, Jack's Copperclad, Supernova, and White Fuseau) in Ohio, during the 2024 growing season. Plant height, tuber number, root system weight, and morphological characteristics were assessed. Variations were observed among the varieties in terms of growth and yield. "Dwarf Sunray" exhibited the highest growth rate, while "Jack's Copperclad" had the lowest. "White Fuseau" yielded the highest tuber count and weight, approximately nine times more than "Jack's Copperclad". Tuber production was positively correlated with root system weight. Varieties also differed in branching patterns, flowering time, tuber shape, and tuber color. This study provides preliminary data for selecting varieties suitable for further research and evaluation in Ohio. The study emphasizes the importance of considering root system development for improved tuber yield and suggests future research should focus on the genetic basis of trait variations and varietal performance under diverse conditions.

With an economic value exceeding $68 billion USD, grapes are third in global horticultural crop production, with production across 93 countries. Recurring incidents of extreme weather conditions are forcing growers to alter conventional production practices. Reduced production areas, shifts in pest management, decreased water availability, increased temperature stress, and extreme weather events have all negatively impacted global grape production. There is a need to develop resilient grape cultivars that can survive the vagaries of nature. In the late 1800s, American horticulture scientist Thomas Volney Munson utilized 10 of the 13 Vitis spp. native to Texas and SW USA to develop cultivars that were adapted to the North American environment and resistant to the pests and pathogens of this area. Munson introduced 300 cultivars, of which 87 remain today. These cultivars have the potential to offer improved fruit quality combined with pest and pathogen resistance, traits that are sought after in modern grape breeding programs. Due to the wide range of parental material used to improve these native grapes, Munson’s cultivars offer a largely untapped genetic resource. By performing whole genome sequencing on the remaining 87 cultivars and the parental lines, we aim to develop a pangenome encompassing the full range of genetic diversity within the remaining Munson cultivars. This study will help clarify the lineage and shed light on any discrepancies in the records. The genomic characterization of the Munson cultivars will also aid in identifying potential resistance genes in these cultivars. This work is expected to secure profitable and resilient production of grapes in the US.

Freezing injuries account for an estimated 15 % of global grape production losses annually, posing a significant challenge to sustainable viticulture. This study investigated phenotypic variation correlated with cold hardiness in two biparental mapping populations to explore potential markers for selecting cold‐hardy genotypes. Quantitative trait locus (QTL) mapping was also performed to identify loci that could accelerate the development of environmentally resilient grape cultivars. We examined two F₁ families—312 hybrids from V. riparia × V. vinifera ‘Fresno Seedless’ and 302 hybrids from V. amurensis × V. vinifera ‘Valley Pearl’. Differential thermal analysis (DTA) was used to assess bud cold tolerance, and we recorded additional traits including bud water content, trunk and cane diameters, and post–bud‐break phenology. Significant variation was observed in cold hardiness and all measured phenotypes. High‐quality genetic linkage maps were generated for both populations, providing a solid foundation for subsequent QTL analysis and marker development. This research offers a sustainable strategy for breeding cold‐hardy grape cultivars that maintain productivity under harsh conditions and speeds breeding efforts in support of climate‐adaptive viticulture.

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.