Location: Cereal Disease Lab2012 Annual Report
1a. Objectives (from AD-416):
Determine resistance of barberry species and cultivars to Puccinia graminis. Develop improved methods of inducing germination of P. graminis teliospores and inoculating barberry plants. USDA-APHIS maintains quarantine against cultivars of barberry and Mahonia that are susceptible to the wheat stem rust fungus. Research is required to determine whether any new barberry cultivar developed for sale in ornamental landscape plantings is susceptible to the wheat stem rust fungus. APHIS established an agreement with the CDL to support research on all new barberry cultivars within the barberry quarantine area to determine thier susceptibility to Puccinia graminis.
1b. Approach (from AD-416):
Conduct field surveys for grass or cereal plants bearing teliospores of Puccinia graminis whose dormancy has been broken by weathering through the winter (exposed teliospores release basidiospores and infect susceptible barberry plants). Evaluate cultivars for symptoms of rust infection of 1-2 weeks after inoculation. Certify new cultivars as resistant if they show no symptoms of rust infection in 12 tests in which susceptible check plants develop abundant rust. Identify possible hybrid barberry cultivars based on plant morphology, grow seedlings from seed of suspected hybrid plants, and test them for segregation of resistance and susceptibility to P. graminis. Test storage procedures for over-wintered teliospores and effects of temperature and moisture treatments for inducing teliospore germination of improved rates of infectious basidiospores for barberry inoculations.
3. Progress Report:
Berberis vulgaris was used in several tests as the positive control. A test was considered adequate when the tester plant was at the optimal stage for infection (i.e. when newly emerged leaves were available) and the positive control (B. vulgaris) had heavy infection in the same experiment. Among 2012 entries, we found Mahonia eurybracteata variety "Minganpi" to be susceptible to Puccinia graminis. Interestingly, this variety was also found to be susceptible to wheat stripe rust pathogen (P. striiformis f. sp. tritici). Other entries were either resistant to stem rust or we could not reach a definitive conclusion. Plants are maintained for further testing when unable to determine whether testing was adequate.