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ABSTRACT
Wheat leaf rust, caused by Puccinia triticina Eriks., is an important wheat (Triticum aestivum L.) foliar disease worldwide. Growing cultivars incorporating genetic resistance is one of the most effective approaches for disease control. Leaf rust resistance gene Lr42 was identified from a wheat relative, Aegilops tauschii Coss. (goatgrass), and has been transferred into hard winter wheat. A previous study identified two markers closely linked to the gene on the short arm of chromosome 1D (1DS) using a near-isogenic population, but flanking markers for Lr42 were not found. In this study, a new mapping population was developed from a cross between 'KS93U50' (a Lr42 carrier) and a susceptible parent, 'Morocco'. An F^sub 2^ population was analyzed with all simple sequence repeat (SSR) markers available from chromosome 1D and F^sub 2^ plants and F^sub 3^ families were evaluated for seedling resistance to isolate PNMRJ, a rust isolate avirulent to Lr42. The F^sub 2^ and F^sub 3^ rust data showed that Lr42 was recessive. Seven markers formed the linkage group on chromosome 1DS. The Lr42 region was flanked by two SSR markers, Xwmc432 and Xgdm33, at 18 cM apart. The results confirmed that Lr42 is positioned on the distal end of chromosome 1DS. The flanking markers for Lr42 should be useful for map-based cloning and marker-assisted pyramiding of Lr42 with other leaf rust resistance genes.
Abbreviations: IT, infection type; MAS, marker-assisted selection; PCR, polymerase chain reaction; SSR, simple sequence repeat.
Leap rust of wheat, caused by Puccinia triticina Eriks., is one of the most important wheat foliar diseases worldwide (Kolmer, 1996). Severe leaf rust epidemics can cause yield losses up to 40% (Knott, 1989). Growing genetically resistant cultivars is one of the most effective strategies to minimize yield losses due to the disease. To date, at least 71 genes for resistance to leaf rust have been cataloged in wheat (Singh et al., 2012). Of these, about half were introgressed from related species. Many of them were from Aegilops tauschii [syn. Triticum tauschii (coss.) Schmalh], the D genome donor of common wheat, including Lr21 (chromosome IDS), Lr22a (chromosome 2DS), Lr32 (chromosome 3DS), Lr39 (chromosome 2DS), and Lr42 (chromosome IDS) (Rowland and Kerber, 1974; Kerber, 1987; Gill et al., 1991; Cox et al., 1994).
Most Lr genes...