Location: Vegetable Crops Research
Project Number: 5090-21220-006-048-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Aug 1, 2026
End Date: Jul 31, 2027
Objective:
The objectives of this project are to screen previously identified late blight-resistant wild species accessions against a broad range of P. infestans lineages to evaluate the durability of the newly identified resistance, and to identify accessions with heritable resistance. In our preliminary work, we have screened over 200 potato wild species accessions (populations) for resistance to P. infestans US-23. Resistance varied widely among accessions, but several belonging to species S. microdontum, S. brevicaule, S. raphanifolium, and S. verrucosum contained robust immunity. The species in this collection were selected because they are sexually compatible with diploid cultivated potato and can easily serve as immediate sources of resistance in diploid potato breeding programs. Further characterization of late blight resistance in this collection using an equally diverse collection of pathogen strains will increase the value of individuals that contain broad-spectrum late blight resistance.
We have also screened 200 accessions belonging to the species Solanum boliviense, which is also sexually compatible with diploid cultivated potato, for resistance to US-23 in whole-plant growth chamber assays. S. boliviense accessions showed a wide range of susceptibility phenotypes but several possessed a high level of resistance. Several late blight R genes did not map to previously known genes, indicating potentially novel resistance.
This research addresses national potato research priorities related to environmentally sound control of diseases and the development of innovative strategies that promote potato production and protection. The project also aligns with USDA’s 2026 research priorities by advancing durable host resistance to emerging pathogens, strengthening crop resilience, and reducing reliance on fungicides.
Research Objectives:
1. Expand testing of late blight resistant germplasm using diverse strains of P. infestans to identify individuals with broad-spectrum resistance.
2. Cross resistant individuals with cultivated diploid potato to determine the heritability of late blight resistance in progeny.
Approach:
Objective 1. Our resistance testing approach uses a protocol that has been previously established and allows for high-throughput screening of potato for late blight resistance (Karki and Halterman, 2021). Our screen will include up to 20 clones from accessions of S. microdontum, S. brevicaule, S. raphanifolium, and S. verrucosum, as well as the ten most resistant S. boliviense clones identified in preliminary experiments. All inoculation experiments will include a susceptible check, the commercial potato variety Desiree. Each clone will be tested against the following P. infestans lineages: US-1, US-7, US-8, US-11, US-18, US-20, US-21, US-22, US-23, US-24, and US-25. Leaves will be scored for resistance based on lesion size at 4 and 5 days after inoculation. Individuals will be considered resistant if the average lesion size is below 1cm in diameter. Individuals will be considered as containing broad-spectrum resistance if they contain resistance to three or more P. infestans lineages.
Objective 2. Individuals containing broad-spectrum resistance will be used as females for crossing with two cultivated diploids: US-W4 and MSFF744-01. The Halterman lab has been using these individuals successfully with wild species to determine fertility and resistance inheritance. Thirty progeny from each cross will be tested against the P. infestans lineages for which they contain resistance in Objective 1. We expect resistance to be inherited in a dominant fashion, so most individuals should be resistant. Resistance will be considered heritable if at least 75% of the progeny are resistant to all the tested lineages.