Location: Vegetable Crops Research
2021 Annual Report
Objectives
Objective 1: Identify and maintain a set of wild potato plants, determine the DNA sequence of each, evaluate the distribution of genetic diversity among these wild potatoes, and use this information to guide breeders in developing improved potato germplasm.
Objective 2: Characterize the set of wild potato plants from Objective 1 for resistance to major potato diseases and pests, including late blight, early blight, Verticillium wilt, and Colorado potato beetle, and map these resistance traits to identify the genetic regions responsible for these traits.
Objective 3: Create hybrids between diploid cultivated potato and the set of wild potato plants from Objective 1, characterize these hybrids for plant and tuber traits, and provide the data to the breeding community to use in developing improved potato germplasm.
Approach
Objective 1: We have identified 10 wild diploid Solanum species with demonstrated utility in potato breeding. Within each species, we will choose 10 accessions for this project based on published resistance data, personal experience, and genebank passport data. Multiple individuals from each wild species will have their S-locus RNase alleles sequenced. Fertility of individuals will be assessed by assaying for pollen viability and production of berries with viable seeds. Disease and pest resistance screens will be carried out on multiple plants in each accession for which a specific resistance trait has been reported previously. Based on these data, twenty individuals from each species will be selected for SNP genotyping, detailed phenotyping and clonal maintenance.
Objective 2: Individual clones identified in Objective 1 will be characterized for resistance to major potato diseases and pests, including late blight, early blight, Verticillium wilt, and Colorado potato beetle. For each disease or pest, we will perform disease inoculations or beetle challenges that generate quantitative resistance scores using previously published methods. R-genes within each individual will be sequenced using RenSeq and the position of R-genes will be mapped to the potato genome.
Objective 3: We will create hybrids by crossing flowers of diploid cultivated potato with pollen from the 200 wild potato plants identified in Objective 1. Resulting hybrids will be characterized for plant growth and tuber traits including size, shape, color and yield. These phenotypic data will be shared with the potato breeding community to use in developing improved potato germplasm. Phenotypic data and genotypic data will be deposited into GRIN and the clones used for this research will be donated to the NRSP-6 potato genebank for use by others.
Progress Report
The U.S. potato genebank stores wild species relatives cultivated potatoes as populations of seeds. How closely related these populations are to each other is unknown but important for potato breeding. Diversity at the S-locus is directly related to the ability of an individual to produce seeds when crossed with another individual or itself. We have begun using capture-based sequencing to dissect the allelic diversity of S-locus RNase genes in wild diploid potatoes. To design and synthesize baits, we identified conserved primer binding sites in functionally annotated S-locus RNase genes from different Solanaceae and amplified ˜140 bp and ˜280 bp DNA fragments from three species (S. chacoense, S. berthaultii and S. tuberosum). We have cloned and sequenced more than 100 plasmids containing these PCR fragments and our results showed these S-locus RNase fragments are highly diverse even within the same species.
We selected 83 potato genebank accessions from ten different species that are thought to have contributed genetic information to cultivated potato. We planted two genotypes from each accession and these clones are being tested for self-compatibility in the greenhouse.
We are conducting a field study to compare greenhouse grown versus field grown seedling tuber families as well as transplants from the same families. Emergence, maturity and flowering notes taken throughout the season and harvest yield/notes at the end of the season will allow us to identify traits that are consistent regardless of seed source and which traits vary.
In order to develop hybrids between wild species and cultivated potato, we have generated dihaploids from Castle Russet, La Belle Russet, Payette Russet, Ranger Russet and Pike and retested previously generated dihaploids of Pacific Russet, Mercury Russet, Russet Norkotah and Silverton Russet. All material was crossed with pollen from diploid clone M6, mixed pollen from tetraploid varieties, and selfed to determine fertility and ploidy. Approximately 15 clones have been selected to move forward with genotyping to confirm ploidy. Generated true potato seed from crosses between dihaploids and selected species clones with resistance to early blight, late blight, verticillium wilt and Colorado potato beetles.
We evaluated the effect of mother plant fertilizer and seed stratrification on true potato seed germination and found that treating seeds with gibberellic acid was superior to stratification as a method for promoting potato seed germination.
Accomplishments
1. Hybrid breeding as a catalyst for change in the potato industry. The potato breeding community is currently exploring the possibility of producing inbred, hybrid potato varieties. If this strategy proves to be feasible, then it will be important to produce high quality true potato seed in large quantity. Improvements in sexual reproduction will be a critical step toward achieving this goal. To support hybrid potato breeding and commercialization efforts, ARS scientists in Madison, Wisconsin, summarized research findings spanning two centuries into the first comprehensive review of potato fertility research as it relates to true potato seed production. As part of this project, best practices that promote potato fertility and seed production were developed as a guide for potato breeders and others who need to generate true potato seed.
Review Publications
Bethke, P.C., Jansky, S.H. 2021. Genetic and environmental factors contributing to reproductive success and failure in potato. American Journal of Potato Research. 98:24-41. https://doi.org/10.1007/s12230-020-09810-3.
Karki, H.S., Halterman, D.A. 2021. Phytophthora infestans (late blight) infection assay in a detached leaf of potato. Bio-protocol. 11(4). Article e3926. https://doi.org/10.21769/BioProtoc.3926.
Nanfeng, L., Wang, Y., Naber, M.R., Bethke, P.C., Hills, W.B., Townsend, P.A. 2021. Hyperspectral imagery to monitor crop nutrient status within and across growing seasons. Remote Sensing of Environment. 255. Article 112303. https://doi.org/10.1016/j.rse.2021.112303.
Mori, M., Maki, K., Kawahata, T., Kawahara, D., Kato, Y., Yoshida, T., Nagasawa, H., Satoh, H., Nagano, A., Bethke, P.C., Kato, K. 2021. Mapping of QTLs controlling epicotyl length in adzuki bean (Vigna angularis). Breeding Science. 71(2):208-216. https://doi.org/10.1270/jsbbs.20093.
Nashiki, A., Jansky, S.H., Bethke, P.C. 2021. The effect of mother plant fertilization and stratification on the germination of true potato seed. American Journal of Potato Research. 98, p. 194-201. https://doi.org/10.1007/s12230-021-09830-7.
Karki, H.S., Abdullah, S., Chen, Y., Halterman, D.A. 2021. Natural genetic diversity in the potato resistance gene RB confers suppression avoidance from Phytophthora effector IPI-O4. Molecular Plant-Microbe Interactions. https://doi.org/10.1094/MPMI-11-20-0313-R.
Halterman, D.A., Kumar, P., Sharma, D., Kumar, A., Verma, H.K., Kumar, A. 2021. Genome-wide identification and expression profiling of basic leucine zipper transcription factors during abiotic stresses in potato (Solanum tuberosum L.). PLoS ONE. 16(3). Article e0247864. https://doi.org/10.1371/journal.pone.0247864.
