1:45:00 PM-2:00:00 PM
Brazilian Germplasm as a Putative New Source of Resistance to Corky Ringspot Disease
Richard Novy, USDA-Agricultural Research Service

               A reciprocal exchange of potato germplasm was conducted between the potato breeding programs of the USDA-ARS, Aberdeen, Idaho and Embrapa Clima Temperado, Pelotas, Brazil. The germplasm exchange allowed the incorporation of new, diverse, disease-resistant germplasm into the breeding programs of each.  Brazilian germplasm sent to Aberdeen represented 1) true potato seed which was germinated for seedling tuber production, with subsequent clonal selection in the field at Aberdeen, and 2) Brazilian breeding clones and varieties which were hybridized at Aberdeen with parents representing the russet market class.  In 2023, Brazilian germplasm comprising four breeding clones and the Brazilian cultivar ‘BRS-Ana’ were evaluated for their response to corky ringspot (CRS) in a heavily infested field in Washington state that has been used for decades for screening for resistance.  CRS is a disease caused by Tobacco rattle virus, with internal necrotic lesions in tubers from virus infection resulting in economic losses to producers.  The percentage of tubers showing internal symptoms of CRS and a rating of the severity of tuber symptoms was taken in the 2023 field screening.  BRS-Ana and one breeding clone were found to be susceptible to CRS, with an additional clone being rated as moderately resistant.  Two breeding clones displayed no symptoms of CRS and were rated as resistant.  Screening in the WA field of the three CRS resistant breeding clones will again be conducted in 2024 to confirm resistance.  The pedigrees of the three CRS resistant clones also will be discussed, including shared ancestry that may be the source of the putative CRS resistance.  In addition, to assess if the observed CRS resistance identified in Brazilian germplasm represents a unique source of resistance not currently being utilized in U.S. potato breeding programs, the three resistant breeding clones will be evaluated with molecular markers associated with CRS resistance.

2:00:00 PM-2:15:00 PM             
Introgression of new sources of resistance to Columbia Root Knot Nematode from Solanum hougasii
Shengwei Hu, Oregon State University

               When present in potato production, Meloidogyne chitwoodi (the Columbia root-knot nematode, CRKN) can cause serious damage to tubers, decreasing their value in both the fresh market and processing industries. Resistance to CRKN was first identified from wild diploid potato species Solanum bulbocastanum accession SB22 and was successfully introgressed into tetraploid potato breeding material. A pathogen of CRKN existing in Columbia basin area, Roza, can break the resistance from SB22. In order to expand the genetic basis of CRKN resistance, previous screenings from our group identified clones from Solanum hougasii (6x) PI283107hou-5mc, PI239423hou-8mc and PI1239424hou-2mc have significantly high levels of resistance against Roza pathotype. The resistant clones underwent pollination with 4x russet bulk pollen (Labelle Russet, Premier Russet, Dakota Trial Blazer, and Rainier Russet varieties). Subsequent hybrid seeds were germinated via tissue culture and subjected to ploidy analysis utilizing plant cell flow cytometry to ascertain chromosome sets. Among the 13 pentaploid F1 progenies examined, two exhibited resistance to CRKN Roza. In BC1 progenies, four clones were identified as highly outcrossing and resistant to the Roza pathotype, yet maintained pentaploidy. A substantial number of BC2 progenies were generated to identify tetraploid-resistant clones.

2:15:00 PM-2:30:00 PM             
Fine Mapping Ryadg resistance from ‘Eva’ Potato
Vidyasagar Sathuvalli, Oregon State University

               Potato Virus Y (PVY) is an important potato pathogen causing severe economic damage. The potato variety ‘Eva’, developed by Cornell University, exhibits resistance to PVY and golden nematode pathotype Ro1. Resistance to PVY in Eva is conferred by Ryadg, a gene introgressed from Solanum andigena and located on chromosome XI. Eva also harbors the H1 locus, located on chromosome V, which provides resistance to golden cyst nematode. A chromosome-level genome assembly of Eva was conducted using PacBio HiFi sequencing and Hi-C scaffolding approaches. The assembly resulted in 1338 scaffolds with an N50 of 7.9 MB and a total size of 1433 MB. The region responsible for extreme resistance to PVY, identified between genetic markers M45 and M6, was located in scaffold h2tg000156l of the Eva genome. Gene prediction and functional annotation of the genome with Braker and eggnog-mapper pipeline predicted 48 resistance (R) gene analogs in this region of interest. Fine mapping is ongoing to identify the specific resistance genes for future transformation studies and develop additional markers for use in marker assisted selection. The genome sequencing of Eva provides valuable insights into the genetic basis of resistance traits against PVY and golden nematode, aiding in the development of breeding strategies for potato crop improvement.

2:30:00 PM-2:45:00 PM
Can Leaf Membrane Integrity Predict Potato Heat Tolerance?
Amaka Ifeduba, Texas A&M University

               Globally, periods of extreme temperatures have become more frequent, longer, and occur earlier, resulting in reduced productivity in cool-season crops like potatoes. Heat stress disrupts plant metabolic processes that affect cell membrane composition, integrity, and protein expression. Increases in cell permeability, ion leakage, and expression of heat shock proteins have been used to measure cell membrane stability and screen for heat tolerance in plants. In potatoes, it is unclear whether leaf membrane stability is correlated with underground tuber productivity under heat stress. The main goal of this study was to evaluate if leaf membrane integrity could serve as a marker for identifying heat-tolerant potato varieties.  The specific objectives were to: a) assess potato leaf membrane conductivity variation of a panel of 226 genotypes exposed to heat. b) identify quantitative trait loci (QTL)/genes responsible for regulating leaf membrane conductivity, and c) assess the differences in expression levels of small heat shock protein 18 (sHSP 18) between representative heat tolerant and heat susceptible genotypes. Electrolyte leakage assay, genome-wide association studies (GWAS), correlation studies, and Western blotting techniques were employed. Significant differences were observed among the 226 genotypes in leaf membrane relative electrolyte conductivity. Eleven QTLs were identified for leaf membrane conductivity, explaining up to 13.8% of the phenotypic variance. Gene annotation in QTL areas indicated associations with genes controlling solute transport through the cell membrane and plant response to abiotic stress tolerance.  This study demonstrated phenotypic variations for leaf membrane conductivity in potatoes, signifying a genetic basis for the trait. Also, the heat-tolerant genotypes had lower electrolyte leakage and higher expression of sHSP 18 under high-temperature stress. Leaf membrane electrolyte leakage was positively correlated with tuber defects and negatively correlated with yield, indicating the potential for indirect selection for heat tolerance in potatoes.

2:45:00 PM-3:00:00 PM
Utilizing Genotyping by Sequencing for Genetic Mapping and QTL Analysis of Potato Cyst Nematode Resistance in a Diploid Wild Potato Population of Solanum brevicaule
Nima Samadi, Oregon State University

               Potato is the world's most economically significant vegetable crop. It faces constant threats from various diseases and pests due to its clonal nature and the challenges in breeding and developing new traits. Among these threats are plant-parasitic nematodes, particularly potato cyst nematodes (PCN), Globodera rostochiensis and G. pallida, which can cause up to 80% yield loss. Developing resistant varieties is the most effective and environmentally friendly method to fight these devastating nematode pests. The U.S. Potato Genebank maintains a rich collection of wild potato species, which are excellent genetic sources to explore for novel resistance against plant pathogens. Indeed, our screening of a large group of wild potato species has identified Y1-5, a Solanum brevicaule clone, that shows robust and broad-spectrum resistance to PCN. Interestingly, a conserved nematode effector called NMAS1 was found to trigger a hypersensitive response (HR) when transiently expressed in the leaves of Y1-5, suggesting that the resistance observed in Y1-5 is likely mediated by one or more resistance (R) genes. We then performed genetic crosses between Y1-5 and a PCN susceptible clone, resulting in a mapping population of 190 diploid progenies. Phenotyping of this Y1-5-derived population using the leaf HR assay showed an approximately 1:1 segregation rate for the HR phenotype, indicating the presence of a single-domain R gene in Y1-5 that recognizes the NMAS1 effector. We have further employed Genotyping by Sequencing (GBS) to genotype this population. Our analysis is underway to identify genomic regions linked to PCN resistance. The development of molecular markers and the subsequent cloning of R genes will help accelerate PCN resistance breeding in U.S. potato varieties.

3:00:00 PM-3:15:00 PM
A review of practices to reduce Potato virus Y in a potato breeding program
Jonathan Whitworth, USDA-ARS

               Of necessity, selection of new potato varieties occurs best in the environment in which they ultimately will be grown. This is typically in commercial production areas where virus pressure, particularly PVY is higher. Selections that become advanced breeding lines may start with unwanted virus levels. Breeder seed used for yield and other breeding trials needs to be free from viruses. Practices that reduce virus levels are of the same type that benefit seed growers in their efforts to produce clean seed. These practices include isolation, separation of seed lots (i.e. inoculum sources), tuber unit planting, winter grow-out tests, and removing PVY symptomatic plants. Extensive serological testing (ELISA) is also used to reduce PVY amounts in breeder seed. Development of PVY resistant varieties remains the best method for combating PVY and for reducing PVY levels in a breeding program as well as the overall potato industry.