IMPROVEMENT IN SCREENING FOR RESISTANCE TO SCLEROTINIA SCLEROTIORUM IN COMMON BEAN THROUGH CHARACTERIZATION OF THE PATHOGEN

摘要

White mold (Sclerotinia sclerotium) is a fungus that can persist in the soil for many years and has a host range of over 400 species. There are currently no sources of complete resistance to this fungus in common beans. Achieving repeatability of resistance expression in bean lines with putative sources of white mold resistance has been enhanced by screening in multiple locations using a white mold monitor nurseries in major bean production areas. The premise of screening these lines in multiple locations is to reduce variable screening results found in using only one location. One aspect of the variable results often recorded is how variable the pathogen is. To increase our understanding of the white mold pathogen variation in each location, isolates were collected from white mold field screening nurseries in eight states and two countries over 4 years and analyzed. The standard greenhouse house testing isolates used in nine states were also submitted. The genetic variation of the isolates was initially tested using mycelial compatibility groupings (MCGs). MCGs test the isolates for clonality by growing the isolates on a special medium. Two isolates are tested together on the media and if they grow together and form a continuous mycelial mat, they are considered compatible. If; however, the two isolates form a barrage line of dead cells where the hyphae met, the isolates are considered incompatible. The original 146 screening nursery isolates as well as the nine greenhouse isolates plus a control isolate 1980 (isolate sequenced by the Broad Institute) were tested using MCGs and a total of 64 MCGs were identified.