SNP Discovery and QTL Mapping of Sclerotinia Basal Stalk Rot Resistance in Sunflower using Genotyping-by-Sequencing

Basal stalk rot (BSR), caused by the ascomycete fungus Sclerotinia sclerotiorum (Lib.) de Bary, is a serious disease of sunflower (Helianthus annuus L.) in the cool and humid production areas of the world. Quantitative trait loci (QTL) for BSR resistance were identified in a sunflower recombinant inbred line (RIL) population derived from the cross HA 441 x RHA 439. A genotyping-by-sequencing (GBS) approach was adapted to discover single nucleotide polymorphism (SNP) markers. A genetic linkage map was developed comprised of 1053 SNP markers on 17 linkage groups (LGs) spanning 1401.36 cM. The RILs were tested in five environments (locations and years) for resistance to BSR. Quantitative trait loci were identified in each environment separately and also with integrated data across environments. A total of six QTL were identified in all five environments: one of each on LGs 4, 9, 10, 11, 16, and 17. The most significant QTL, Qbsr-10.1 and Qbsr-17.1, were identified at multiple environments on LGs 10 and 17, explaining 31.6 and 20.2% of the observed phenotypic variance, respectively. The remaining four QTL, Qbsr-4.1, Qbsr-9.1, Qbsr-11.1, and Qbsr-16.1, were detected in only one environment on LGs 4, 9, 11, and 16, respectively. Each of these QTL explains between 6.4 and 10.5% of the observed phenotypic variation in the RIL population. Alleles conferring increased resistance were contributed by both parents. The potential of the Qbsr-10.1 and Qbsr-17.1 in marker-assisted selection (MAS) breeding are discussed.