Genetic association of leaf rust resistance gene Lr34 with adult plant resistance to stripe rust in bread wheat

Near-isogenic Thatcher lines (viz., RL6058, RL6077, and Line 920) carrying gene Lr34 for leaf rust resistance, Frontana, and various other wheat cultivars carrying Lr34 displayed adult plant resistance to stripe rust in Mexico. F2 populations or F3 fines from several intercrosses of wheats carrying Lr34 did not segregate for susceptibility to stripe rust and leaf rust, indicating that at least one resistance gene was common in each parent. An evaluation of F3 lines for stripe rust and leaf rust, from the crosses of stripe rust and leaf rust susceptible Jupateco 73S with stripe rust and leaf rust resistant Condor and Jupateco 73R, showed linked segregation for the two diseases. For each disease, resistance was conferred by one partially dominant gene. Because Lr34 is located on chromosome 7D, the linked Yr gene is designated Yr18. RL6058, RL6077, Line 920, Condor, or Jupateco 73R could be used as tester genotypes for Yr18. The durable adult plant stripe rust resistance of Anza, a related sib of the parent of Condor, is postulated to be attributable to Yr18, which is widespread in cultivars from the International Maize and Wheat improvement Center germ plasm and South American wheats. An additional adult plant stripe rust resistance gene was present in both Sonoita 81 and Tonichi 81.