Inheritance of leaf rust resistance in the wheat cultivars AC Majestic, AC Splendor, and AC Karma

The wheat cultivars AC Majestic, AC Splendor, and AC Karma were developed and licensed for production in western Canada in the mid-1990s. Leaf rust, caused by Puccinia triticina, is an important pathogen of wheat throughout North America. Virulent isolates of P. triticina are selected and increase following the release of wheats with specific resistance genes, which eventually reduces the effectiveness of the resistance. Knowledge of the genes that condition leaf rust resistance in wheat makes it easier to add additional resistance genes to breeding germplasm. The objective of this study was to identify the leaf rust resistance genes in these three cultivars. The three cultivars were crossed with the susceptible wheat 'Thatcher', and the F₁ plants were backcrossed to 'Thatcher'. The backcross F₂ (BCF₂) families were tested for segregation of leaf rust resistance in seedling tests with specific P. triticina isolates. The BCF₂ families were also tested for segregation of leaf rust resistance as adult plants in a field rust nursery that had been inoculated with a mixture of P. triticina virulence phenotypes. 'AC Majestic' was determined to have the seedling resistance gene Lr16 and the adult plant resistance gene Lr13. 'AC Splendor' was determined to have Lr13, Lr16, and the adult plant resistance gene Lr34. 'AC Karma' was determined to have Lr13, Lr16, and the adult plant resistance gene LrTb. All three cultivars had genes Lr13 and Lr16, which reflect a lack of genetic diversity for leaf rust resistance in western Canada spring wheats. The results of the study indicate that additional leaf rust resistance genes need to be crossed into the spring wheat germplasm to provide new cultivars with high levels of leaf rust resistance.