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.