Genetics of rape (Brassica napus L.) resistance to blackleg
Blackleg, harmful and widespread disease of rape, is caused by two species of fungal pathogen Leptosphaeria maculans and L. biglobosa, L. maculans does more significant losses to crop. Both pathogens are hemibiotrophs. They can persist for many years in the stubble and crop residues. The source of primary infection for rape seedlings are ascospores and picnidio-spores. Blackleg develops on all plant organs. The disease manifests on the leaves and pods as dry gray oval spots, on the stems may occur most damaging defeat of plants (stem cancer), on the roots - dry root rot. The severity of symptoms increased at high temperatures, so global warming leads to greater threat of blackleg. L. maculans genome was sequenced and seven avirulence genes were cloned. Rapeseed genome also sequenced but only one gene was cloned of 14 known major resistance genes to L. maculans. The interaction of avirulence genes with complementary resistance genes in Brassica - L. maculans system occurs by «gene to gene». All known major rape resistance genes to L. maculans were localized in A - genome, but resistance loci were identified also in C-genome of rape by association mapping. Some resistance genes were introgressed into rape from other species (B. rapa, B. juncea, B. nigra). Besides the major genes of juvenile (race-specific) resistance there were identified minor genes of quantitative (partial, field) blackleg rape resistance. It is necessary to intensify the research of rape resistance genetics to L. biglobosa which causes significant yield loss in countries with high summer temperatures.