Quantitative Trait Loci Associated with Isolate Spe cific and Isolate Non-Specific Partial Resistance to Sclerotinia sclerotiorum in Sunflower

Abstract

Basal stem rot caused by Sclerotinia sclerotiorum (Lib.) de Bary is one of the most important diseases of sunflower. Quantitative trait loci (QTL) implicated in partial resistance to two isolates of S. sclerotiorum (SSU107 and SSKH41) were investigated using F 9 recombinant inbred lines (RILs) from the cross bet ween sunflower parental lines PAC2 and RHA266. Experiments were conducted in comp letely randomized design with 3-6 replications under controlled conditions. The r eaction of genotypes to basal stem rot disease was evaluated by measuring the percentage o f necrosis area three days after inoculation. Combined analysis of experiments showe d significant interactions between sunflower genotypes and S. sclerotiorum isolates suggesting that partial resistance to S. sclerotiorum should be isolate-specific in sunflower. QTLs were mapped using an updated high-density SSR and SNP linkage map. The map consi sted of 210 SSRs and 11 gene- derived markers placed in 17 linkage groups (LGs). The total map length was 1,653.1 cM with a mean density of 1 marker per 7.44 cM. A tota l of 14 QTLs were detected for partial resistance to two isolates. The phenotypic variance explained by QTLs (R 2 ) ranged from 0.10 to 9.85. The sign of additive gene effect s showed that favorable alleles for partial resistance to isolates came from both paren ts. Six QTLs were common between two isolates on LGs 1, 8 and 17, whereas the others were specific for each isolate. Co- localized QTLs on LG 1 were linked to the glutathio ne S-transferase gene (GST). The co- localized QTLs for partial resistance to basal stem rot isolates could be good candidates for marker assisted selection (MAS). Keyword: Basal stem rot, Helianthus annuus L., isolate specificity, partial resistance, QTL mapping.