The introgressed segment carrying rust resistance genes Yr17, Lr37 and Sr38 in wheat can be assayed by a cloned disease resistance gene-like sequence

A cloned gene sequence (Vrga1D), with features of the nucleotide-binding-si te leucine-rich repeat class of disease resistance (R) gene sequence super family, was previously shown to belong to a family of five gene members der ived from a Triticum ventricosum Ces. (syn. Aegilops ventricosa Tausch) seg ment in wheat (Triticum aestivum L.). This gene family was introgressed, to gether with the linked rust resistance genes Yr17, Lr37 and Sr38 from T. ve ntricosum, to wheat chromosome 2AS. An independently derived T. ventricosum segment carrying a leaf rust resistance gene in a French wheat cultivar, w as shown to exhibit a rust resistance response equivalent to Lr37 as well a s Yr17 and Sr38. DNA probes from different regions of the Vrga1D clone cons istently detected the presence of RFLPs associated with the introgressed se gment carrying the resistance genes Yr17, Lr37 and Sr38 present in diverse wheat genotypes from Australia, Canada, France and the UK. Our results show ed that the transfer of the T. ventricosum-derived Vrga1 gene members and t he rust resistance genes were always accompanied by the loss of a correspon ding set of Vrga1-related gene members in recipient wheat cultivars presume d to be of homoeoallelic origin. A PCR assay, based on sequences from the 3 '-untranslated region of a Vrga1 gene member isolated from the T. ventricos um donor line of the introgressed segment, was developed. The PCR assay det ected the presence of the introgressed rust resistance genes across the div erse wheat backgrounds and should be useful in marker-assisted selection in wheat breeding.