2011 Annual Report
1a.Objectives (from AD-416)
1) Identify resistance to white mold in adapted common bean lines;
2) Assess the variation in common bean isolates of Sclerotinia sclerotiorum from major bean production areas.
1b.Approach (from AD-416)
Multiple field location and greenhouse screening tests will be used to determine white mold reaction of putative sources of resistance. These lines will be provided by bean breeders and pathologists from recombinant inbred line populations, interspecific hybridizations, introgressions from wild bean Phaseolus vulgaris, and breeding lines. Field plots will be located in areas of Oregon, Michigan, Wisconsin, North Dakota, Nebraska, Washington and France with a history of white mold. All field locations plus Idaho, Colorado and New York will conduct greenhouse tests. Variations in common bean isolates of S. sclerotiorum will be assessed by determining mycelial compatibility groups of isolates from bean growing areas in the U.S., and comparing them with compatibility groups from white mold screening nurseries in the same area, e.g. Red River Valley, ND. The aggressiveness of S. sclerotiorum isolates of the above isolates will be determined by the straw test. The intraspecific variation in S. scleroriorum greenhouse isolates and field isolates collected at each screening trial site and bean growing areas will be determined by the use of four microsatellite-specific primers. Pathogen variation knowledge will guide use of specific screening isolates.
This project was initiated on June 1, 2007, research is ongoing, and the overall objectives are to identify sources of resistance to Sclerotinia sclerotiorum in adapted common bean lines and assess the genetic variation in common bean isolates of S. sclerotiorum. ADODR monitoring activities to evaluate research progress included phone calls, meetings with the cooperator, and an annual meeting held each year in January.
Bean cultivars with intermediate resistance and or avoidance to white mold (WM) would reduce disease losses and require no input costs for growers. Thus, one project goal was to identify sources of resistance in adapted and nonadapted common bean lines utilizing standardized greenhouse screening methods and field nurseries across major USA bean production regions. Multi-site testing provided data for identifying four bean lines with moderately high resistance and two pinto lines with intermediate resistance. Three adapted dry bean lines also exhibited avoidance to WM. In the past four years, a snap bean and nine dry bean lines were released for public and private breeders/companies. A second project goal was to assess variation in common bean isolates of Sclerotinia sclerotiorum. To address this goal, we devised a unique study on pathogen variation across bean-production areas that tests the hypothesis that pathogen isolate variation within and between test sites influences identification of WM resistance. Mycelial compatibility groupings (MCGs), aggressiveness, and microsatellites (SSRs) were used to identify genotype and phenotype differences in the isolates that can influence stability of identified WM resistance over time and location. Collecting isolates from specific bean host lines replicated at each resistance screening site permitted us to assess within and between location variation. High aggressiveness and genetic variability (measured by MCGs and microsatellites) of pathogen isolates within and between field screening nursery locations and greenhouse test isolates has been found. Another hypothesis we are testing is that the isolates involved in screening reflect characteristics of those found in local grower fields. When isolates from screening nurseries in each of three states were compared with grower field isolates in the same state, there were significant differences in aggressiveness. Our database of characterized isolates facilitates new isolate characterization and provides critical information for choosing isolates in resistance screening. The expected outcome is a set of characterized isolates for plant breeders and pathologists searching for unique and common clones with more or less aggressiveness to use in screening for WM resistance. The isolate information will be posted on the SI and Bean Improvement Cooperative websites and isolates will be stored and made available at the University of Nebraska-Lincoln, Plant Pathology Department.