CLONING OF MOLECULAR MARKERS FOR DISEASE RESISTANCE IN SUNFLOWER, HELIANTHUS-ANNUUS L

A candidate-gene approach to analyse the resistance of plants to phyto pathogenic fungi is presented. The resistance of sunflower (Helianthus annuus L.) to downy mildew (Plasmopara halstedii) shows a gene-for-ge ne interaction (monogenic resistance), whereas resistance to white rot (Sclerotinia sclerotiorum) is quantitative, with different levels of resistance for different plant parts. By homology cloning, probes were obtained homologous to some plant resistance genes (nucleotide bindin g site-like, NBS, genes and serine-threonine protein kinase-like, PK, genes). These clones were used as probes for linkage mapping of the co rresponding genes. It was demonstrated that at least three NBS-like lo ci are located on linkage-group 1, in the region where downy mildew re sistance loci have been described. Quantitative trait loci for S. scle rotiorum resistance to penetration or extension of the mycelium in dif ferent tissues were studied in three crosses. Major QTLs for resistanc e were found on linkage group 1, with up to 50% of the phenotypic vari ability explained by peaks at the map position of the PK locus, 25 cM from the downy mildew loci.