Location: Genetic Improvement for Fruits & Vegetables Laboratory
Project Number: 8042-21000-305-017-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Jun 1, 2023
End Date: May 31, 2025
Objective:
Common scab is an economically devastating disease of potato in the United States caused by pathogenic Streptomyces bacteria that produce the phytotoxin Thaxtomin A. Soil-based detection of the pathogen is possible through qPCR amplification of the Thaxtomin A biosynthetic genes TxtAB, but routine detection is not available to growers to help determine planting plans based on the presence and amount of common scab pathogens. We will address this problem via:
1. Determine the stability of pathogenic Streptomyces populations in soil.
2. Identify soil factors associated with common scab disease severity and pathogen population levels.
3. Establish pathogenic Streptomyces soil qPCR assay with three plant disease diagnostic labs.
Approach:
1. Cooperator and ARS will determine the stability of pathogen populations in greenhouse pot and potato fields within and between growing seasons. Field trials will be conducted at the ARS Aroostook research farm in Presque Isle, Maine and the Penn State Russell Larson Experimental Ag station in Pennsylvania Furnace, PA. All selected field sites are known to have common scab infestations. At each site, five replicate blocks (one block = three five-hill plots) will be planted with a common scab-susceptible potato cultivar, five blocks planted with a resistant potato cultivar, and five blocks kept fallow. Soil samples will be collected from each five-hill plot immediately prior to planting, halfway through the growing season, and immediately prior to harvest (135 total soil samples for each field site). A qPCR detection assay will be utilized to quantify the pathogen population of each soil sample to determine if pathogen populations change throughout a growing season and if potato presence and potato cultivar disease susceptibility alter pathogen populations. Common scab disease scores will be quantified from each five-hill plot (45 per field site) at harvest to determine which soil sampling timepoint most accurately predicted disease pressure in the field.
2. Field soil from each plot described in Objective 1 will be sent for physical and chemical analysis to the University of Maine, Pennsylvania State University. Covariate analyses will be performed to identify soil factors associated with disease severity and pathogen populations.
3. To translate the improved and validated TxtAB detection assay into an immediately valuable tool for potato growers across the United States, we will establish the detection assay with plant disease diagnostic labs at University of Maine, and Penn State University. Protocols will be shared with the lead diagnosticians at those laboratories and known soil samples from Objective 1 (both field and greenhouse samples) will be sent to the diagnostic labs for blind testing.
