The inheritance of leaf rust resistance in the wheat cultivars 'Superb', 'McKenzie' and 'HY644'

Understanding the genetic resistance to wheat leaf rust, caused by Puccinia triticina, in Canadian wheat cultivars is critical for maximizing resistance in future-bred cultivars. This knowledge also helps to predict the impact of changes in virulence to specific resistance genes within the P. triticina population. 'Superb' and 'McKenzie' are two of the most popular high-yielding wheat cultivars in Canada. 'HY644' has moderate resistance to Fusarium head blight (caused primarily by Fusarium graminearum). All three of these cultivars have been used extensively as parents in Canadian wheat breeding programmes. To analyze the nature of resistance in these cultivars, they were crossed and then backcrossed to the susceptible cultivar 'Thatcher'. The BC1F3 populations were inoculated at the seedling and adult plant stages with various P. triticina races to determine the number and identity of the resistance genes in each cultivar. Allelism tests, to confirm the postulated genes, were performed by crossing each cultivar to the 'Thatcher' isolines containing the postulated genes and analyzing the F2 progeny for rust resistance. 'Superb' was demonstrated to have genes Lr2a and Lr10, 'McKenzie' had Lr10, Lr13, Lr16 and Lr21, and 'HY644' had Lr1, Lr17, Lr34 and an unknown resistance gene.