Abstract
Basal stem rot (BSR), caused by Sclerotinia sclerotiorum and S. minor, is one of the most important fungal diseases of sunflower (Helianthus annuus L.) causing significant yield losses worldwide. Using resistant cultivars is the most effective method to manage BSR in the field. Therefore, identification of resistant genotypes and genomic regions related to the disease resistance is necessary for employment in the field and for development of resistant cultivars. In this study, the reaction of 100 oilseed sunflower lines was investigated against three isolates from each of the S. sclerotiorum and S. minor species in controlled conditions and association analysis of resistance traits was performed using retrotransposon-based DNA markers. The sunflower germplasm exhibited various reactions against the fungal isolates as the mean necrosis percentage in basal stem of the lines ranged from 30.67 to 100. The genotypes H156A/H543R, 110 and 8A×/LC1064C were resistant to the isolates of both species. Population structure analysis subdivided the genotypes into two subpopulations. Association analysis using general and mixed linear models identified 15 and 14 loci, respectively, which were significantly (P ≤ 0.01) associated with resistant traits. Phenotypic variance explained by QTLs (R2) ranged from 1 to 23%. The markers UF1, LTR1064-A13, LTR1061-UBC818 and LTR1064–65 were commonly associated with the traits conferring resistance to more than one fungal isolate. This was the first study on QTL mapping of genomic regions responsible for resistance to S. sclerotiorum and S. minor using retrotransposon-based DNA markers in and provided an evidence for effectiveness of these markers in association analysis of sunflower. The QTLs and the markers associated with the resistance traits can be useful in marker-aided programs to develop sunflower cultivars with effective resistance to BSR caused by the two Sclerotinia species.
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