Mapping of Stem Rot Resistance in Peanut Indicates Significant Effect for Plant Architecture Locus

Stem rot, caused by the Sclerotium rolfsii, imposes severe yield losses in peanuts (Arachis hypogaea L.) worldwide. Breeding for resistance is challenging because not enough is known about mechanisms for resistance. The goals of this study were to (a) evaluate the field resistance of recombinant inbred lines derived from a resistant x susceptible cross, (b) associate quantitative loci (QTLs), and (c) reveal potential mechanisms for resistance. Lines were inspected during 3 yr in field conditions. Plants were manually inoculated and rated for three parameters: disease level, number of damaged plants/center, and disease power. Significant effects were found for the lines and the environment in all three parameters. Heritability and year-to-year correlations were highly significant, suggesting a consistent response of the lines to the stem rot pressure. Quantitative trait loci mapping was performed based on a previously constructed genetic map. Overall, 20 significant QTLs were found for the resistance parameters, concentrating in four locations on chromosomes A07, A03, B03, and B05. Out of the four loci, three were reported in previous studies with different genetic backgrounds suggesting a wide effect. The B05 QTL was the strongest, with the phenotypic variation explained of 11.6-21.7%. Interestingly, this QTL is colocalized with a previously identified major locus for branching habit trait. An additional field trial performed on 14 lines found a significant branching habit effect, wherein bunch-types lines were more resistant than spreading-types, suggesting that plant architecture can be a possible factor influencing the infection rate of S. rolfsii on the field level.