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Quantitative Trait Loci Analysis of Resistance to Sclerotinia sclerotiorum in Sunflower

First, third, and fourth authors: Institute for Crop Science and Plant Breeding, Justus-Liebig-University of Giessen, Heinrich-Buff-Ring 26-32, D-35392 Giessen, Germany; and second author: State Plant Breeding Institute, University of Hohenheim, D-70593 Stuttgart, Germany

A quantitative trait loci (QTL) analysis of resistance to Sclerotinia sclerotiorum was carried out with 283 sunflower (Helianthus annuus) F_2:3 families derived from a cross between a resistant (SWS-B-04) and a highly susceptible sunflower inbred line. For that purpose, a genetic map based on 195 amplified fragment length polymorphism and 20 simple sequence repeat markers was constructed. The map has a size of 2,273.5 centimorgans and comprises 17 linkage groups, 12 of which could be associated to already defined linkage groups. The heads of sunflower F₃ families were artificially inoculated by using sclerotinia mycelium in three field environments. The lesion length was measured in centimeters 1 week postinoculation and head rot was scored according to a 1-to-8 head rot scale 2 weeks postinoculation. Using the composite interval mapping procedure, three QTL for lesion length and two QTL for head rot could be identified. These QTL explain 10.6 to 17.1% of the total phenotypic variance.