Analyses of QTL associated with resistance to Sclerotinia sclerotiorum and Diaporthe helianthi in sunflower (Helianthus annuus L.) using molecular markers

Most traits exhibit continuous variation resulting from the action of multiple genes modified by the environment. Quantitative trait loci (QTL) analysis consists in determining the location and number of genes that condition such quantitative traits and estimating the magnitude of individual gene effect by the use of analytical methods and detailed linkage map. Sclerotinia sclerotiorum and Diaporthe helianthi are important pathogens of sunflower in France causing white rot and stem canker. Restriction fragment length polymorphism (RFLP) and amplified fragment length polymorphism (AFLP) were used to construct two linkage maps of cultivated sunflower based on the progenies of 335 F2 plants from intra specific cross XRQ x PSC8. Genetic factors that condition resistance to leaf and capitulum resistance to S. sclerotiorum and to D. helianthi, and other agronomic characters are analysed on 220 XRQ x PSC8 F3 families. This QTL analysis will provide new insights on the location and organisation of characterised QTL (eventually common QTL for both pathogen resistances). Genetic mapping of disease resistance genes should help to improve the efficiency of plant breeding and will lead to a better understanding of the molecular basis of resistance.