Evaluation Of Thinopyrum Intermedium-derived Resistance And Mapping Of Stripe Rust Resistance Gene In Wheat

Stripe rust(Yr) and powdery mildew (Pm), caused by Puccinia striiformis f. sp. tritici (PST) and Blumeria graminis f. sp. tritici (Bgt), respectively, are very damaging fungal diseases of wheat (Triticum aestivum L.) worldwide. The growing area of wheat in China ranks second only to rice as one of the most important staple food crops. Breeding for resistance is one of the most successful ways to protect wheat varieties against these diseases. As the prevalence of the new Chinese PST and Bgt pathotypes CYR31, CYR32, E20, and E21, most of the reported resistance genes, except for Yr5, Yr10, Yr15, Yr24, Yr26, and Pm2+6, Pm16, Pm20, Pm21, Pm43 are, however, ineffective against the above races, thereby posing a grave threat to Chinese wheat production. Therefore, the search for new and effective sources of resistance and their transfer is needed to their use in breeding of wheat.Thinopyrum intermedium has been hybridized extensively with wheat and proven to be a valuable source of genes for disease resistance to stripe rust and powdery mildew. A program for introgression of alien resistance genes was initiated at the Institute of Crop Genetics, Shanxi Academy of Agricultural Sciences in 1992, which aimed to transfer resistances to powdery mildew and stripe rust into wheat from Th. intermedium. To date, many multi-resistance lines have been developed by crossing susceptible wheat cultivars with resistant partial amphiploids as donor parents and Pm40 and Pm43 were transferred from Th. intermedium into cultivated wheat. The objectives of this study wereâ…°) to evaluate the seedling and adult plant resistance to powdery mildew in eighty-four wheat lines derived from an resistant partial amphiploid TAI7045;â…±) to determine the inheritance, chromosomal location, and linkage to molecular markers, of gene(s) for resistance to stripe rust in the Th. intermedium-derived line CH7114. The following is the main results obtained.1. The evaluation of seedling and adult plant responses to powdery mildew showed that, among eighty-four homogeneous BC1F5-derived wheat lines derived from the cross of Jing 411/TAI7045//Jinmai 33, sixty-seven, accounting for 79.8% of all the materials tested, were resistant at the seedling and adult stages to Bgt isolates E09, a prevalent pathotype and the most widely virulent pathotypes in China E20 and E21, which are virulent to most of the Pm genes. The powdery mildew response in the resistant lines was similar to its donor TAI7045, and the wild parent, suggesting that the powdery mildew resistance conferred by the above wheat lines was derived from Th. intermedium. The cytological analyses showed that the resistant lines and their F1 hybrids involving Chinese Spring wheat had 2n=42 of somatic chromosome numbers and a regular pairing per pollen mother cell at meiosis, indicting that the resistant lines was stable in cytology, and their chromosome structure largely identical to that of wheat.2. CH7114 is wheat advanced line resistant to stripe rust and powdery mildew, which was developed by crossing Th. intermedium-derived partial amphiploid TAI7047 with susceptible wheat cultivar. The evaluation of resistance reactions demonstrated that, at the seedling and adult stages, CH7114 was resistant to four PST isolates including CYR32, the prevalent and most widely virulent in China, and the resistance derived from Th. intermedium. Genetic analysis of the F1, F2 and BC1 populations revealed that resistance was controlled by a single dominant allele. By the linkage analysis of a segregating F2 population, the gene responsible for stripe rust resistance, temporarily designated YrCH7114, was mapped to the short arm of wheat chromosome 5D (5DS) and flanked by two co-dominant genomic SSR markers (Xbarc130 and Xgwm205). Their most likely order was Xbarc130-YrCH7114-Xgwm205 at 9.7 and 14.6 cM, respectively. As Yr40, the only other known Yr gene on 5DS, was transferred from Aegilops geniculata and its specificity is different from that of YrCH7114, it was concluded that YrCH7114 is probably a new stripe rust resistance gene.