GENETICS OF ADULT-PLANT RESISTANCE OF LEAF RUST IN FRONTANA AND 3 CIMMYT WHEATS

Wheat (Triticum aestivum L.) cultivar 'Frontana' and three globally leaf rust resistant CIMMYT spring bread wheats, 'Parula', 'Trap', and 'Mango', which displayed seedling susceptibility to Mexican pathotypes TCB/TD and (or) TBD/TM of Puccinia recondita f.sp. tritici and which displayed high levels of adult-plant resistance, were genetically analyzed. The four wheats were intercrossed and crossed with seedling and adult-plant susceptible cultivars 'Inia 66' or 'Yecora 70', and also with 'RL6058', a tester for leaf rust resistance gene Lr34. Adult-plant resistance to leaf rust appeared to be based on four additive genes in 'Frontana' and three additive genes in each of the other resistant wheats. Gene Lr34 was confirmed to be present in all four wheats and appeared to be important in conferring adult-plant resistance in conjunction with other partially effective adult-plant resistance genes. Some of these latter genes appeared to be common in the four wheats, since limited segregation occurred when intercrossed. Genes Lr3, Lr10, Lr13, and Lr26 appeared to be independent of the adult-plant resistance. The resistance is expected to be durable, since the source of Lr34 and the additional genes was traced to 'Frontana', which has retained its field resistance since its release in 1943.