Genetic analysis and SSR mapping of stem rust resistance gene from wheat mutant D51

Abstract

Wheat (Triticum aestivum L.) stem rust caused by Puccinia graminis f. sp. tritici is one of the main diseases of wheat worldwide. Wheat mutant line D51, which forms a highly susceptive cultivar ‘L6239’ to the three races notated and cultured with immature embryos, shows resistance to prevailing races 21C3CPH, 21C3CKH, and 21C3CTR of P. graminis f. sp. tritici in China. In this study, the number and the expression stages of the resistance genes in mutant D51 were studied using inoculation identification and microsatellite (SSR) marker analysis. Two F1 populations from the crosses of D51 × L6239 (60 individuals) and D51 × Chinese Spring (60 individuals), their F2 populations (185 and 175 individuals respectively) at the seedling stage, and one F2 population derived from the cross of D51 × L6239 (194 individuals) at the adult stage were inoculated with pathogen race 21C3CPH to test for resistance. All F1 individuals of the two crosses were immune to stem rust at both seedling and adult stages. The response pattern of the three F2 populations showed that the R:S segregation ratio was 3:1, suggesting that the stem rust resistance of D51 is controlled by a single dominant gene, and is expressed during the entire growth period. The identification of the stem rust resistance by the F3 progeny test confirmed the credibility of the F2 population test. Segregating populations and small population analyses were used to identify chromosomal regions and molecular markers linked to the gene by the SSR marker method. A total of 675 SSR markers and 185 individuals of the D516L6239 F2 population were used to search genetically linked markers to the target gene. Using Mapmaker 3.0 and Map-draw with Kosambi’s function and other options set at default values, molecular mapping revealed that the gene was located on chromosome 5DS, linked with and flanked by two SSR markers, Xgwm190 and Xwmc150, at 18.58 and 21.33 cM, respectively. It has been reported that only one stem rust resistant gene, Sr30, is located on the wheat chromosome 5DL, and that it has no resistance to 34C2MKK and 34C2MFK, while the parent L6239 of mutant D51 has no resistance to 21C3CPH, 21C3CTK and 21C3CTR, but has resistance to 34C2MKK and 34C2MFK. The results above indicate that the gene identified in the study might be a novel resistance gene to stem rust, tentatively designated as SrD51.