Identification and mapping stripe rust resistance gene YrLM168a using extreme individuals and recessive phenotype class in a complicate genetic background

The identification and characterization of resistance genes effective against stripe rust of wheat is beneficial for modern wheat breeding programs. Molecular markers to such genes facilitate their deployment. The variety Milan has resistance that is effective against the predominant stripe rust races in the Sichuan region. Two resistant and two susceptible F-8 lines from a cross between Milan and the susceptible variety Chuannong 16 were used to investigate inheritance of the Milan resistance. Three F-2 populations were developed from crosses between the resistant lines and their susceptible sibling lines (LM168a x LM168c, LM168c x LM168a, LM168b x LM168d) and used for genetic analysis and molecular mapping of the genes for resistance. The stripe rust resistance in LM168a and LM168b was conferred by a single dominant gene, temporarily designated as YrLM168a. Forty-five extreme susceptible plants from the F-2 families of LM168d x LM168b were genotyped with 836 simple sequence repeat (SSR) markers to map YrLM168a. YrLM168a was mapped in chromosome 6BL. The nearest flanking markers Xwmc756 and Xbarc146 were 4.6 and 4.6 cM away from the gene at both sides, respectively. The amplification results of twenty extreme resistant (IT 0) and susceptible (IT 4) F-2 plants of LM168c x LM168a and LM168a x LM168c with marker Xwmc756 further validated the mapping results. The study suggested that extreme individuals and recessive phenotype class can be successfully used for mapping genes, which should be efficient and reliable. In addition, the flanking markers near YrLM168a should be helpful in marker-assisted breeding.