QTL mapping of partial resistance to basal stem rot in sunflower using recombinant inbred lines

Basal stem rot, caused by Sclerotinia sclerotiorum (Lib.) de Bary, is an important cause of yield loss in sunflower (Helianthus annuus L.). Quantitative trait loci (QTLs) implicated in partial resistance to basal stem rot disease were identified using 116 recombinant inbred lines (RILs) from the cross between the sunflower parental lines PAC2 and RHA266. The RILs and their parents were arranged in a completely randomized design with six replications and inoculated with a moderately aggressive isolate (SSU107) of S. sclerotiorum under controlled conditions. QTLs were mapped using a recently developed high-density simple sequence repeat/ amplified fragment length polymorphism (SSR/AFLP) sunflower linkage map. Analysis of variance showed highly significant differences among the sunflower genotypes for susceptibility to basal stem rot. The frequency distribution of genotypes for susceptibility to disease showed continuous patterns, suggesting that resistance is controlled by a polygenic system. Transgressive segregation for resistance occurred in this cross. Composite interval mapping analysis revealed 7 QTLs for percentage necrotic area, localized on 7 linkage groups. The effects of QTLs were small to moderate indicating a polygenic control of the studied character. However, like any other quantitative trait, it is necessary to confirm the position of the QTLs and to carry out fine-scale mapping before marker assisted selection (MAS) can be done. LG8 and LG16 are good candidates for further analysis to develop molecular markers for resistance to Sclerotinia disease.