Identification of resistance to Rhizoctonia limb rot in a core collection of peanut germ plasm

Diseases caused by Rhizoctonia solani lead to significant reductions in peanut yields and quality throughout the world. A subset of accessions from the peanut germ plasm core collection plus the commercial cultivars Florunner, Southern Runner, Georgia Browne, and Georgia Green were evaluated for resistance to limb and seedling hypocotyl infections caused by R, solani. Georgia Green and core accessions 95 (PI 497351), 197 (PI 331326), 208 (PI 274193), 244 (PI 343361), 246 (PI 343398), and 524 (PI 288178) had levels of resistance comparable to Georgia Browne, the only commercial cultivar reported to have partial resistance to Rhizoctonia limb rot. Eleven core accessions, representing the full range of disease expression, and the commercial cultivars were evaluated in growth chambers to quantify their susceptibility to seedling hypocotyl infections and to determine if evaluating seedlings could serve as a primary screening method to identify potential sources of limb rot resistance. The most resistant core accessions to seedling hypocotyl infections were 234 (PI 159664) and 366 (PI 268968), and the most resistant commercial cultivar was Georgia Green. There was not a significant correlation between resistance to limb rot in the field and the severity of hypocotyl infections in growth chambers, indicating that resistance to hypocotyl infections is not a good indicator of resistance to Rhizoctonia limb rot.