ANALYSES OF QUANTITATIVE TRAIT LOCI ASSOCIATED WITH RESISTANCE TO SCLEROTINIA-SCLEROTIORUM IN SUNFLOWERS (HELIANTHUS-ANNUUS L) USING MOLECULAR MARKERS

Restriction fragment length polymorphism and isoenzyme markers were us ed to investigate quantitative trait loci involved in sunflower resist ance to mycelial extension of Sclerotinia sclerotiorum on leaves and c apitula. Seed weight, oil content and flowering data were also evaluat ed. Four quantitative trait loci were demonstrated for leaf resistance and two for capitulum resistance. One of these zones appears involved in resistance to both types of S. sclerotiorum attack while the other s appear specific for resistance of one part of the plant. Two quantit ative trait loci were detected or seed weight, three for oil content a nd three for flowering date. Individual quantitative trait loci explai ned 9% to 48% of the phenotypic variability, confirming the polygenic basis of the quantitative traits studied. Overall, the quantitative tr ait loci explain 60% of the genetic variation for leaf resistance and 38% for capitulum resistance to S. sclerotiorum. One linkage group is particularly interesting since it includes quantitative trait loci for all the five quantitative traits measured. Hypotheses for linkage ver sus pleiotropy and consequences of all the results in resistance breed ing are discussed.