Pyramiding Stem Rust Resistance Genes into South African Wheat Cultivars

Wheat production in Africa is threatened by the evolution of new races of Puccinia graminis f. sp. tritici (Pgt) including Ug99 and its variants. Development of resistant wheat varieties is the most effective and economic strategy to control this disease. Pyramiding several resistance genes into adapted cultivars is considered a more effective method to combat new races. Resistance genes Sr2 and Sr26 are effective against all races of Pgt including Ug99 and its derivatives. Sr25 is effective against most races. The use of molecular markers makes it easy to pyramid multiple rust resistance genes into a single genotype as opposed to using conventional rust screening method. The objective of the study was to use diagnostic molecular markers to pyramid three stem rust resistance genes into three South African wheat cultivars. For pyramiding, the donor sources with three genes were first crossed to adapted cultivars, and then backcrossed until generating BC₃F₂ and BC₃F₃ lines. The markers csSr2 and Gb were used to select for Sr2 and Sr25, respectively. The marker Sr26#43 and a 6A-specific marker BE518379 were used to select for Sr26. A total of 69 lines at the BC₃F₂ generation carried all three genes. After validation of these lines for homozygosity at BC₃F₃, a multi-field trial will be conducted for yield and quality, alongside with their recurrent parents. The germplasm developed will be made available to wheat breeders.