Field Evaluation and QTL Mapping of Stem Rot Resistance in Cultivated Peanut and Wild-Derived Germplasm

Stem rot, caused by Agroathelia rolfsii (syn. Sclerotium rolfsii), is a major soilborne disease of peanut (Arachis hypogaea L.). We evaluated wild-derived germplasm for field resistance and identified associated genomic regions. Twenty-eight genotypes, including Israeli cultivars, three wild-derived induced allotetraploids and their backcross derivatives, were evaluated under artificial field inoculation over two seasons. Disease level differed significantly among genotypes, with consistent rankings between seasons (r = 0.88). The induced allotetraploids and several derived lines showed significantly low disease levels, whereas most commercial cultivars developed severe disease. Stem rot reduced pod yield by 49% on average, and disease level was negatively correlated with yield (r = −0.63). Near-isogenic line-based analysis indicated that bunch-type architecture may reduce disease development. NIFA-R, derived from ValSten1 (A. valida × A. stenosperma), combined low disease levels with relatively high yield under inoculated and non-inoculated conditions. QTL mapping in a Hanoch × NIFA-R F2:3 population detected 18 significant trait–QTL associations for sickness grade, symptomatic plants and inoculation-center sickness grade, with a consistently supported shared association on chromosome 13. NIFA-R contributed the favorable allele at 16 of 18 significant QTL associations, although their specific ancestry remains unresolved. These results demonstrate the value of wild-derived resistance resources and identify preliminary QTL regions for further validation toward marker-assisted selection.