A 2DS Chromosome Carries a Complex of Leaf Rust Resistance Alleles in Wheat

Most leaf rust resistance genes in wheat are inherited independently of each other. However, two or more genes on the same chromosome may show varying degrees of linkage. At the Lr2 locus on 2DS, there are three known resistance alleles, Lr2a, Lr2b and Lr2c. The Lr15 gene was recently mapped in the vicinity of Xgwm4562 and Xgwm102 by Dholakia et al. (2013). The Lr2 locus also mapped within the similar vicinity (Tsilo et al. 2014). To determine if the two genes are either tightly linked or allelic, allelism test was carried out. A cross between RL6016 (Lr2a) and RL6052 (Lr15) was created and the F₂ lines were inoculated with race B115. Both parents and 1670 F₂   lines showed resistance to B115 with infection types of ;1 and 1. A lack of observing susceptible individuals out of that large number of lines suggested that the Lr15 gene is another allele of Lr2, adding to Lr2a, Lr2b, and Lr2c. Because these alleles provide resistance against a larger number of races in South Africa and elsewhere in the world, molecular markers linked to these alleles, reported in 2013 and 2014 studies, should facilitate the deployment of these alleles in wheat breeding programmes.