Location: Vegetable Crops Research
2019 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
Five accessions of four diploid wild potato species were chosen based on published literature establishing their value as sources of resistance to Colorado potato beetle. Up to 20 plants per accession were grown in a greenhouse. Detached leaves were used for a beetle feeding assay. In collaboration with scientists at Agriculture and Agri-Foods Canada, USDA Grand Forks, and Michigan State University, plants were screened for presence of glandular trichomes and resistance compounds (acyl sugars and glycoalkaloids). Variability among plants for these compounds was identified, as was beetle feeding and mortality. Resistance trials will be repeated in June 2019. Preliminary results indicate that high levels of resistance are present in each accession. The most resistant plants are being maintained clonally. Individuals with resistance to late blight, as identified in Objective 1, are also being used for pollen collection.
We have also evaluated 20 accessions for resistance to late blight using a detached leaf assay. We rated individuals within each accession as susceptible, partially resistant, or resistant. When available, two resistant individuals were selected for clonal maintenance in the collection of 200 individuals. When no resistance was identified in an accession, additional accessions of the same species will be screened for resistance.
Accomplishments
1. Transfer of resistance to common scab from wild to cultivated potato. Common scab, caused by the soil-borne bacterium Streptomyces scabies, is a persistent threat to the potato industry. It causes unsightly pits on the surface of potatoes and results in economic losses and waste due to grade-out for all potato market classes. There is no chemical control option and cultural control methods do not produce consistent results. We identified strong scab resistance in a wild relative of potato and demonstrated that resistance can be transferred to cultivated potato. Through a series of crosses, we incorporated resistance into parental lines and released them to breeders (our stakeholders) who are using them to develop resistant cultivars. The development of cultivars with enhanced levels of resistance to common scab will address a major cause of marketable yield loss for potato growers and will provide more attractive potatoes to consumers.
Review Publications
Marand, A.P., Jansky, S.H., Gage, J.L., Hamernik, A.J., de Leon, N., Jiang, J. 2019. Residual heterozygosity and epistatic interactions underlie the complex genetic architecture of yield in diploid potato. Genetics. 212(1):317-332. https://doi.org/10.1534/genetics.119.302036.
Fulladolsa, A., Charkowski, A., Cai, X., Whitworth, J.L., Gray, S.M., Jansky, S.H. 2019. Germplasm with resistance to Potato Virus Y derived from Solanum chacoense: Clones M19 (39-7) and M20 (XD3). American Journal of Potato Research. 96(4):390-395. https://doi.org/10.1007/s12230-019-09719-6.
