Location: Genetic Improvement for Fruits & Vegetables Laboratory
Project Number: 8042-21000-305-026-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Aug 15, 2025
End Date: Aug 14, 2026
Objective:
1. Survey incidence of common scab and powdery scab in the Pacific Northwest and identify species of common scab pathogens
2. Evaluate efficacy of fluazinam (Omega) and pentachloronitrobenzene (Blocker 4F) against common scab in ND and ID field trials
3. Evaluate select cultivars for resistance to the identified most predominant common scab species in the PNW in controlled greenhouse trials
Approach:
To determine whether the increased incidence of common scab in the Washington, Oregon, and Idaho is associated with the emergence of novel lineages of Streptomyces pathogens, we will perform an extensive survey of disease presence across the region. Streptomyces pathogens will be isolated from approximately ten tubers exhibiting common scab symptoms from each of approximately 20 different fields. A total of 300 to 400 isolates will be collected from lesions and DNA extracted using established protocols. The presence of the Thaxtomin biosynthetic genes will be checked using PCR, and the species of Thaxtomin-positive isolates will be determined using either whole-genome sequencing or multilocus sequence analysis to determine the predominant species/lineages in the region.
Parallel field trials will be implemented to test the efficacy of PCNB and fluazinam for management of local common scab pathogen populations in ND fields with known disease pressure. Soil will be collected in each field plot before planting and tested for the infestation levels of both the powdery and common scab pathogens. The field trials will be randomized complete blocks with split plots. The main plot will be the two potato cultivars highly common scab susceptible and moderately susceptible. Subplots will include mock treatment, 48 fl oz/a Omega (fluazinam), 6 pt/a PCNB, and 10 pt/a Blocker (PCNB). Each subplot will include 4 rows, each 30 feet long. Two doses of PCNB and two differentially susceptible cultivars of potato are included in the design to optimize ability to identify conditions in which PCNB treatments impact disease outcomes. At harvest, 20-30 tubers from each field trial site will collected identification of Streptomyces species responsible for common scab. This identification informs which Streptomyces species for which the collected field trial data is directly relevant.
Two to three of the most predominant species, or sub species lineages, of Streptomyces will be tested in greenhouse trials for virulence on six potato cultivars in replicated single pot (one pathogen strain per pot) inoculation assays. A survey of growers will be conducted to determine the select cultivars. Results from the greenhouse assay will be used to inform selection of cultivars for future field trials in common scab endemic fields.