Location: Genetic Improvement for Fruits & Vegetables Laboratory
Project Number: 8042-21000-305-011-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Nov 1, 2021
End Date: Jun 30, 2024
Objective:
Common scab is a major bacterial disease of potato in North Dakota and all other potato growing regions in the United States. The objective of this project is to characterize the population structure of the causative agent of common scab in North Dakota and identify effective disease management tools for mitigating grower losses to common scab.
1. Perform in-depth survey to identify the Streptomyces causing common scab in North Dakota.
2. Characterize the within-field diversity of phytopathogenic Streptomyces at select sites.
3. Determine resistance of potato cultivars commonly grown in North Dakota to the Streptomyces pathogens found in the state.
4. Optimize low-dose 2,4-D applications for controlling common scab in the field and identify factors that limit efficacy.
5. Identify soil chemical and physical properties that affect common scab incidence and disease.
Approach:
1. Diseased tubers will be collected from 20-30 different field sites across North Dakota following the 2022 and 2023 harvest. Streptomyces will be isolated from diseased lesions and placed in the ARS Streptomyces culture collection. PCR will be used to identify putative phytopathogenic Streptomyces and Multilocus Sequence Analysis (MLSA) used to identify species. Select strains will be selected for whole-genome sequencing for additional characterization of the strains and strain diversity. Common scab severity and incidence will be indexed at all field sites selected for sampling.
2. The same approach as Objective 1 will be employed to sample two selected field sites to the point of absolute saturation for identify Streptomyces. Approximately 100 diseased tubers from each of these two field sites will be used for isolating and identifying several hundred phytopathogenic Streptomyces. 10-20 genomes of isolates from one of the field sites, including isolates that appear identical based on the MLSA results will be sequenced to determine if the population of Streptomyces of the same species within the same field site are clonal or harbor additional diversity. Common scab severity and incidence will be indexed.
3. 5-10 of the cultivars of potato determined to be the most commonly grown in North Dakota through grower surveys will be grown in pots containing individual phytopathogenic Streptomyces strains determined to be present in North Dakota in Objective 1. Disease incidence and severity will be measured in replicated pot assays and the most resistant cultivars, the most aggressive pathogens, and notable strain x cultivar interactions will be determined.
4. The efficacy of low-dose 2,4-D sprays for common scab control will be determined at two field sites in 2022 and 2023. A modified split plot design with four to eight replicates will be used to allow for the inclusion of barrier rows to limit exposure of mock-treated plants to 2,4-D through drift. The main plot will be treatment conditions (timing and dosage of 2,4-D). Two levels of treatment will be tested to see if higher levels of 2,4-D improve common scab control without negatively impacting plant health. Prior to the 2022 growing season, a greenhouse trial will be performed to determine the highest levels of 2,4-D that can be sprayed without noticeable phytotoxicity. Three treatment timing points will be tested (approximately two weeks before tuber initiation, tuber initiation, and two weeks after tuber initiation). At harvest, common scab incidence and severity in each plot will be evaluated.
5. Soil cores will be collected from the field sites sampled in Objectives 1, 2, and 4. Soil cores will be sent for soil analysis and a principal component analysis will be performed to identify soil parameters associated with the observed common scab incidence and severity and presence/absence of specific pathogen species groups. These identified soil parameters will also be used as covariates to better analyze the field results from Objective 4.
