Genetic analysis and development of molecular markers for a resistance locus to Mycosphaerella graminicola in wheat

Septoria tritici blotch (Septoria blotch) caused by the ascomycete Mycosphaerella graminicola (anamorph: Septoria tritici Roberge in Desmaz.) is a major disease of wheat in the US and many humid wheat growing areas of the world. Host resistance is the most effective means of controlling this disease. Several sources of Septoria blotch resistance have been identified. Genetic analysis coupled with development of DNA markers that are closely linked to the specific Septoria blotch resistance genes are beneficial for efficient utilization of these host resistance genes in wheat improvement. The objectives of this research were to: (1) determine the inheritance of Septoria blotch resistance of wheat germplasm line SO852, (2) develop RAPD markers closely linked to the Septoria blotch resistance gene(s), and (3) map the Septoria blotch resistance gene(s) in the wheat genome. Analysis of backcross BC1F1 populations and BC1F 2 families indicated that Septoria blotch resistance of SO852 is conditioned by a single dominant gene. Testcross analysis indicated that this gene is allelic to Septoria blotch resistance gene Stb1 of Sullivan, which was derived from Bulgaria 88. Two RAPD markers, H19520 and G71200, were identified that are tightly linked to that locus using bulked segregant analysis and 148 BC1F1 plants. Using wheat nullisomic-tetrasomic lines, RAPD marker H19520 was located on chromosome 5B. The marker was further located in a region on the long arm of 5B delineated by chromosome breakpoints at fraction length 0.59 and 0.75, using 5B deletion lines. RAPD marker H19520 is thus useful for mapping the resistance gene of SO852 and for marker assisted selection in wheat improvement.