Screening of U.S Mini Cores for Resistance Against Sclerotinia Blight in Peanut.

Sclerotinia sclerotiorum is a necrotrophic soil borne fungal pathogen that causes Sclerotinia blight in many peanut growing regions. The U.S mini cores collection provided was initially screened in a greenhouse to identify resistant genotypes. A total of 107 cores were screened by using a detached leaf method as well as a whole plant inoculation method. In the detached leaflet method, each core had 6 leaflets per trial, repeating each trial 3 times for a total of 18 leaflets per core. In the whole plant inoculation method, the average disease incidence and disease severity was measured every other day up to two weeks for each core, repeating 3 times. For control, Valencia A variety was used. In both methods, two day-old, 5mm diameter PDA plugs infected with S. sclerotiorum was used when plants were at the 3-4 true leaf stage. In detached leaflets method, a plug was placed at the center of each leaf after moistening sterilized whatman filter paper with 2ml distilled water in a 9 mm diameter petri-dish. Cores were scored from 0 to 4, 0= no disease and 4= 100% leaf area infected. In whole plant inoculation, two plugs were placed between lateral leaf and main stem opposite to each other. Cores were scored from 0 to 5, 0= no disease and 5= plant death. Cores were categorized as highly susceptible, susceptible, partial resistant and resistant and data was analyzed in excel. Based on the results obtained from both methods, after 8 days post-inoculation, more than 85% of cores were highly susceptible and none showed resistance or even partial resistance to S. sclerotiorum. From detached leaflet method, cores 15- 1001, 15-1002, 15-1043, 15-1047 and 15-1052 had the lowest disease score with 2.7 so they were classified as susceptible cores. From whole plant inoculation method, cores 15-1030, 15-1005, 15-1032, 15-1044, 15-997 had the lowest disease severity percent with 62%, 72%, 73%, 75%, 77% respectively. Therefore, all cores showed susceptibility towards S. sclerotiorum.