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ARS Home Midwest Area St. Paul, Minnesota Plant Science Research Research





- Samac, Deborah - Debby
- Plant Genetic Resources, Genomics and Genetic Improvement (301)

Research Project: **Location:
                            Plant Science Research** Project Number: 5062-21000-034-002-S
                        
                        Project Type: Non-Assistance Cooperative Agreement Start Date: Jul 1, 2023
                        
                        End Date: Jun 30, 2025 **Objective:**
                        
                        1.1. Establish a reliable phenotyping platform for oat stem rust screening.
1.2. Inventory the diversity and level of resistance (or a lack thereof) in current cultivars and breeding germplasm from regional breeding programs.
1.3. Identify and characterize new sources of major and adult plant resistance genes.
2.1. Monitor the movement of Xanthomonas translucens in wheat plants in field trials using seeds inoculated with rifampicin resistant strains.
2.2. Validate molecular methods to detect and quantify bacteria from infected seed using qPCR.
2.3. Visualize where the pathogen is located within infected wheat through microscopy.
2.4. Curate and expand a collection of Xanthomonas translucens strains from the Upper Midwest. **Approach:**
                        
                        An oat stem rust phenotyping platform that includes field and seedling evaluations will be developed. A set of Puccinia graminis f. sp. aveane (Pga) races with different virulence spectra will be used to characterize germplasm for resistance at the seedling stage and postulate resistance genes. Two oat stem rust nurseries will be established that will accommodate 2,000 entries per year. Every year, elite breeding lines will be evaluated at the field nursery and at the seedling stage to generate critical stem rust reaction data for breeders. This stem rust screening system, once established, will be made open to screen breeding germplasm beyond the Upper Midwest. To identify and characterize new sources of stem rust resistance, mapping populations derived from crosses using parents that potentially carry adult plant resistance (APR) genes will be genotyped with the a commercial 3K SNP array.
Resistant lines will be forwarded to regional breeding programs. Additionally, a selection of 1,000 cultivated oat accessions from diverse geographic origins deposited at the USDA National Small Grains Collection (NSGC) will be phenotyped at the stem rust field nurseries in year 1. Accessions exhibiting resistance to moderately susceptible reactions will be evaluated in year 2 at both field nurseries and at the seedling stage against the complete set of Pga races. Accessions carrying potential major or APR genes will be crossed with susceptible parents to develop mapping populations.
The movement of X. translucens in wheat plants in field trials will be tracked using seeds inoculated with rifampicin resistant strains. Wheat (cv. Mayville, susceptible) seeds will be inoculated with a rifampicin resistant strain and sown in field plots at St. Paul. Leaves will be sampled upon emergence throughout the growing season, bulked by sampling date, and plated in dilution series on bacterial growth medium amended with rifampicin. This trial will be repeated over two field seasons. To determine the extent of seed transmission, seed from infected field plots will be tested with a PCR assay. On-farm variety trials with naturally occurring Bacterial Leaf Streak (BLS) infections will be an additional source of infected seed. Scanning electron microscopy (SEM) will be utilized to determine where bacterial cells reside in seeds. In cooperation with the University Imaging Center (UIC), seed surfaces, cross-sections, and longitudinal sections of wheat and barley seeds will be viewed with SEM technology. The collection of Xanthomonas translucens strains from the Upper Midwest will be increased and curated. The collection will be expanded by scouting and collecting samples from BLS infections in MN. This work includes characterization of X. translucens isolates through molecular and in plant assays. Strains will be provided to the BLS research community.


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