Location: Small Grains and Potato Germplasm Research
2021 Annual Report
Objectives
This project intends to produce improved potato germplasm and varieties with emphasis on the predominant market class for the western U.S. which is characterized by long tubers and russet skin. Improved varieties will be suitable for potato processing, as well as fresh consumption. The objectives below will be the specific focus for the next five years for the project scientists Novy and Whitworth:
Objective 1: Use conventional and genomic technologies to develop improved potato germplasm and varieties representative of the primary market classes grown in the western U.S. with the following enhancements being emphasized:
• Subobjective 1A: Improve Disease and Pest Resistance
• Subobjective 1B: Improve Tuber Qualities for Processing and Fresh Use
• Subobjective 1C: Reduce Production Inputs
• Subobjective 1D: Enhance Nutritional Value
Objective 2: Accelerate breeding for resistance to potato pathogens and pests using genomic technologies.
Objective 3: Identify and utilize pathogen and pest resistance specific to potato cyst nematode (PCN) and tuber necrotic viruses (Potato virus Y, Potato mop-top virus, and Tobacco rattle virus), and characterize foliar and tuber responses of potato varieties and germplasm to the tuber necrotic viruses.
Approach
Objective 1 is non-hypothesis driven research with the goal of developing potato germplasm and varieties with tuber qualities, disease and pest resistance, and sustainable production that is superior to current industry varieties, with emphasis on primary market classes grown in the western U.S. Varieties and germplasm obtained from other breeding programs, as well as breeding clones of species and their enhanced progeny from ARS collaborators, will be hybridized with adapted parent material in our program using a modified backcross where different cultivated parent clones are used in each backcross to minimize inbreeding depression. Progenies will be screened over multiple years for enhanced traits and agronomic performance in replicated multi-site field trials in the western U.S. Use of molecular technologies (i.e. SNP microarrays, genotyping by sequencing, MAS, and genomic selection) will accelerate development of improved germplasm and varieties. Breeding clones with enhanced traits compared to industry standard varieties will be released as new varieties or as breeding germplasm. As needed, additional germplasm from outside of our program will be requested and utilized as parental material in hybridizations to generation unique populations that expedite trait enhancement.
Objective 2 is non-hypothesis driven research utilizing molecular markers with close linkage to genes conferring pest and disease resistance. Molecular markers to resistance genes for Potato virus Y, Potato leafroll virus (PLRV), and potato cyst nematode will be utilized in marker-assisted selection (MAS). Genomic technologies, including SNP microarrays, will be used to identify new genes and quantitative trait loci (QTLs) for resistance. Mapped genes and QTLs will be sequenced and primers developed for MAS. Development of new MAS protocols is important for breeding resistance to emerging diseases (i.e. Potato mop-top virus (PMTV) and zebra chip disease. MAS application will fast-track identification of resistant individuals and facilitate the development and release of potato germplasm and varieties with enhanced disease resistance. If markers in the literature prove unsatisfactory for MAS, then we would work to identify suitable markers, as was previously done by our project for a PLRV resistance gene.
Objective 3 is non-hypothesis research focusing on the screening of diverse potato germplasm and characterization of infection-response to potato cyst nematode and three tuber necrotic viruses: PVY, (PMTV), and Tobacco rattle virus (TRV). Field evaluations for response to infection will be conducted by our project (PVY), as well as with collaborators in Washington and North Dakota (PMTV and TRV). Resistant individuals will be utilized in the breeding program as parents with incorporation of resistance conducted utilizing the modified backcross method describe in Objective 1. If levels of resistance for PCN and the tuber necrotic viruses cannot be identified within project germplasm, then new parental material with desired characteristics will be obtained from the U.S. Potato Genebank and other national and international public and private breeding programs
Progress Report
In support of Objective 1, research continued on several thousand potato breeding clones that were planted, maintained, harvested, and evaluated at multiple sites throughout the United States in yield and disease screening trials in the project, with state and industry collaborators evaluating their merit for release as new potato varieties. Seed of all breeding clones was maintained at three seed increase sites in Idaho, with testing of seed for viruses being conducted prior to spring planting to mitigate virus infection in seed. An advanced breeding clone, AO06191-1, originating from hybridizations conducted by our program, was released with university researchers in Idaho, Oregon, and Washington, as Rainier Russet. Rainier Russet has a high marketable yield and long tuber dormancy, which is an advantageous trait for maintaining tuber quality in long-term storage. This variety also has cold sweetening resistance, meaning that when held at low temperatures that reduce sprouting, less starch is converted to reducing sugars, resulting in lighter-colored, and better-quality fries. Color across fries of Rainier Russet is also consistently uniform relative to industry standards for Ranger Russet and Russet Burbank.
One hundred and fifty-four parental clones representing a total of 628 plants were grown in a greenhouse in 2021 at Aberdeen, Idaho, and hybridizations made among them for the generation of true potato seed, which is the starting point for the generation of new populations in our breeding program. One thousand and eighty-nine families, having a combined total of 1,364,095 true potato seed, were extracted from potato berries, counted, and organized in the Fall of 2020 from hybridizations conducted that year.
In the Spring and Fall of 2021, seedlings from true potato seeds were planted in greenhouses to produce seedling tubers for planting in the field in 2022. In May 2021, a total of 92,049 seedling tubers generated from potato seedlings in 2020 were planted in the field for fall selection. Each plant from a tuber represents unique genetics with the potential to be developed as a new variety. Within these numbers are directed hybridizations made specifically for disease and pest resistance, as well as for better tuber quality, enhanced nutritional qualities, traits which require less fertilizer, water, and other inputs in order to make potato more sustainable. These research efforts contribute to all four sub-objectives of Objective 1.
National Fry Processing Trials (NFPT), financially supported by the potato processing industry, included 63 entries (breeding clones) from seven states in 2021. Twenty-nine of those entries originated from this project. The NFPT program seeks to identify advanced breeding clones that perform well under multiple environments and have low tuber sugars (reducing sugars) for processing. Our project serves as one of six trial sites for the NFPT where entries were planted, maintained, and data collected and provided to the national project. These NFPT research efforts directly contribute to Sub-objective 1B.
In support of Objective 2, marker assisted selection (MAS) was conducted, beginning with second-field year material. Molecular markers that indicate the presence of genes for resistance to Potato virus Y (PVY), Potato leafroll virus, and potato cyst nematode were tested, and this information was used during field selection to facilitate the breeding for resistance to these diseases and pests. A ‘multiplex’ assay that allows breeding lines to be tested for the presence of three PVY resistance genes simultaneously, rather than having to conduct three separate tests, was developed by our project and is being used for MAS. This multiplex assay identified a PVY resistance gene in russet germplasm that previously had not been known to be present in this potato market class, aiding in the subsequent development of PVY-resistant russet-skinned varieties. PVY causes yield and tuber quality defects, and control with pesticides is ineffective. This virus is transmitted by multiple species of aphids which can rapidly acquire and transmit the virus prior to being adversely impacted by the application of insecticides. Plant resistance is an important component in an integrated approach for the control of this virus. Our project also identified regions of potato chromosomes associated with tuber shape and starch content, as well as late blight resistance, which will be used in developing MAS for these important traits. This research supports Sub-objectives 1A and 1B and Objective 2.
In support of Objective 3, Potato mop top virus (PMTV) research was expanded to include two PMTV-infested field trial sites, rather than one in the previous year. Testing for the percentage of symptomatic tubers with spraing (necrotic tuber tissue associated with PMTV) and asymptomatic tubers is being conducted in infested fields in Idaho with PMTV-resistant potato varieties Castle Russet, Pomerelle Russet, and Mesa Russet. One of the sites is the same field which was used previously in 2019, and results will be used in developing a publication that characterizes levels of PMTV resistance/tolerance to infection among the three varieties and examines the correlation between disease level in the field at planting and PMTV transmission and symptoms after harvest. The ability to identify infested fields and to be able to use resistant or insensitive varieties will offer growers options in potato production in PMTV-infested fields.
PVY research was published in the American Journal of Potato Research that detailed foliar and tuber symptoms associated with multiple strains and isolates of PVY collected from across the United States. The varieties included in the study represent 62% of the seed acreage grown in the United States. Results showed that many varieties do not express necrotic tuber symptoms when infected with different PVY strains. This publication provides a valuable resource to growers when assessing the risk to best manage fields that have varieties sensitive to PVY tuber symptoms. Documentation of foliar symptoms will benefit growers and seed certification officials who rely on visual inspections for detection of PVY. This research supports Sub-objective 1A and Objective 3.
Accomplishments
1. New potato variety, Rainier Russet, with high marketable yield, long tuber dormancy, and attractive tubers. ARS researchers in Aberdeen, Idaho, along with their university colleagues in Idaho, Washington, and Oregon, released the new potato variety, Rainier Russet, with plant variety protection (PVP) for the variety to be sought. This variety produces high marketable yields in both early- and full-season harvests, allowing for its use in a greater diversity of growing regions. Rainier Russet has cold-induced sweetening resistance and uniformity of fry color, allowing its use for longer-term storage prior to production of French fries. This is an improvement over other industry standard varieties, where conversion of starch to sugar results in a darker processed product. Rainier Russet is also notable for having long tuber dormancy, which promotes the retention of tuber quality in storage with reduced sprouting. Rainier Russet has an attractive tuber, making this variety also suitable for use for fresh consumption, as well as for processing.
Review Publications
Vigue, S.J., Scheuring, D.C., Koym, J.W., Rush, C.M., Tamborindeguy, C., Miller, J., Douches, D.S., Novy, R.G., Vales, M. 2020. Identification of tetraploid potato clones with good processing quality among genotypes with reduced zebra chip disease symptomatology. American Journal of Potato Research. 97:565-579. https://doi.org/10.1007/s12230-020-09804-1.
Zhang, C., Zarka, K., Zarka, D., Whitworth, J.L., Douches, D.S. 2021. Expression of the tomato pot-1 gene confers potato virus Y (PVY) resistance in susceptible potato varieties. American Journal of Potato Research. 98:42-50.
Spear, R., Novy, R.G., Whitworth, J.L., Stark, J.C., Pavek, M.J., Knowles, R., Knowles, L., Charlton, B.A., Sathuvalli, V., Yilma, S., Thornton, M., Olsen, N., Brant, T., Wang, Y. 2021. Galena russet: A long dormancy, dual purpose potato cultivar exhibiting low asparagine, cold-sweetening resistance, and enhanced protein content. American Journal of Potato Research. 98:51-63. https://doi.org/10.1007/s12230-020-09817-w.
Pandey, J., Scheuring, D.C., Koym, J.W., Coombs, J., Novy, R.G., Thompson, A.L., Holm, D.G., Douches, D.S., Miller Jr, C.J., Vales, I.M. 2021. Genetic diversity and population structure of advanced clones selected over forty years by a potato breeding program in the USA. Scientific Reports. 11. Article 8344. https://doi.org/10.1038/s41598-021-87284-x.
Whitworth, J.L., Gray, S.M., Ingram, J.T., Hall, D.G. 2021. Foliar and tuber symptoms of U.S. potato varieties to multiple strains and isolates of Potato virus Y. American Journal of Potato Research. 98:93-103. https://doi.org/10.1007/s12230-020-09820-1.
