Molecular mapping of adult-plant race-specific leaf rust resistance gene Lr12 in bread wheat

Wheat (Triticum aestivum) gene Lr12 provides adult-plant race-specific resistance to leaf rust caused by Puccinia triticina. It is completely linked or identical to Lr31, which confers seedling resistance only when the complementary gene Lr27 is also present. F-2 and F-2-derived F-3 families were developed from a cross between the susceptible variety Thatcher and TcLr12, an isoline carrying Lr12. Of 230 F-3 families, 55 were homozygous resistant, 115 were segregating for resistance, and 60 were susceptible to P. triticina, fitting a monogenic 1:2:1 segregation ratio. Lr12 was mapped on chromosome arm 4BL and was flanked by markers Xgwm251 and Xgwm149 at distances of 0.9 and 1.9 cM, respectively. Using linked markers and wheat deletion stocks, Lr12 was located in deletion bin 4BL-5, FL = 0.86-1.0, comprising the terminal 14% of 4BL. The markers will be useful for following Lr12/Lr31 in crosses and for further mapping studies.