MOLECULAR MAPPING OF RESISTANCE TO LEPTOSPHAERIA-MACULANS IN AUSTRALIAN CULTIVARS OF BRASSICA-NAPUS

Doubled haploid (DH) lines together with a cotyledon bioassay were emp loyed for the molecular analysis of resistance to the blackleg fungus Leptosphaeria maculans in the Australian Brassica napus cultivars Shir alee and Maluka. We used bulked segregant analysis to identify 13 RAPD and two RFLP markers linked to the resistance phenotype and mapped th ese markers in the segregating DM population. Our data suggest the pre sence of a single major locus controlling resistance in the cultivar S hiralee, confirming our previous results obtained from Mendelian genet ic analyses. In addition, preliminary mapping data for the cultivar Ma luka also support a single locus model for resistance and indicate tha t the resistance genes from 'Shiralee' and 'Maluka' are either linked or possibly identical. The molecular markers identified in this study should be a useful tool for breeding blackleg resistant varieties usin g marker-assisted selection, and are the essential first step towards the map-based cloning of this resistance gene.