Abstract:

Stem rust caused by Puccinia graminis f. sp. tritici is one of the main diseases of wheat (Triticum aestivum L.) worldwide. Wheat mutant line D51, form a highly susceptive cultivar ‘L6239’ to the three races notated and cultured with immature embryo, shows resistance to prevailing races 21C3CPH, 21C3CKH, and 21C3CTR of P. graminis f. sp. tritici in China. In this paper, number of the resistance genes in mutant D51 and the expression stages were studied with 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 seedling and one F₂ populations derived from the cross of D51×L6239 (194 individuals) at adult stage were inoculated with pathogen race 21C3CPH to test their 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 fit 3:1, suggesting the stem rust resistance of D51 controlled by a single dominant gene, and expressed in whole growth period. The identification to stem rust resistance by F3 progeny test confirmed the credibility of F2 population test. Segregating populations and small population analyses were used to identify chromosomal region and molecular markers linked to the gene by SSR markers method. A total of 675 SSR markers and 185 individuals of D51×L6239 F₂ population were used to search genetically linked makers to the target gene. Using Mapmaker3.0 and Map-draw with Kosambi’s function and other options left at default values, molecular mapping revealed that the gene was located on the chromosome 5DS, and linked with and blanked by two SSR markers Xgwm190 and Xwmc150 at 18.58 and 21.33cM, respectively. According to references reported, the only one stem rust resistant gene Sr30 is located on the wheat chromosome 5DL, and has no resistance to 34C2MKK and 34C2MFK, and parent L6239 of mutant D51 is without resistance to 21C3CPH, 21C3CTK and 21C3CTR, but with resistance to 34C2MKK and 34C2MFK.The results above indicate that the gene identified in this paper might be a novel resistance gene to stem rust, designated SrD51 tentatively.

Key words: Wheat (Triticum aestivum L.), Stem rust, Resistance gene, SSR marker