Identification Of Slow Stripe Rust Resistance In Chinese Wheats And Molecular Mapping Of New Stripe Rust Resistance Gene YrZH84

Stripe rust, caused by Puccinia striiformis f. sp. tritici (PST), is one of the most damaging diseases in common wheat (Triticum aestivum L.). Identification of seedling and slow stripe rust resistance genes in wheat cultivars or advanced lines is important for gene deployment and breeding cultivars with stripe rust resistance to control the disease. The research included two parts, identification of seedling and slow stripe rust resistance genes in 145 cultivars and lines as well as molecular tagging of stripe rust resistance genes in Chinese wheat line Zhou8425B.A total of 145 Chinese leading wheat cultivars, newly released cultivars, and advanced lines included in this study were collected from the autumn-sown wheat regions in 12 provinces. In all, 98 lines were inoculated with 26 pathotypes of Puccinia striiformis f. sp. tritici (PST) for postulation of stripe rust resistance genes at the seedling stage. One hundred thirty five wheats were planted in two locations to characterize their slow rusting resistance to stripe rust in the 2003-2004 and 2004-2005 cropping seasons. The results indicated that genes Yr2, Yr3a, Yr4a, Yr6, Yr7, Yr9, Yr26, Yr27, and YrSD, either singly or in combinations, were postulated in 72 genotypes, whereas known resistance genes were not identified in the other 26 accessions. The resistance genes Yr9 and Yr26 were found in 42 and 19 accessions, respectively. All lines postulated to have Yr9 also amplified a SCAR marker for rye chromatin and Yr26 was derived from Chinese line γ80-l (Triticum turgidum L.) and its derivatives such as 92R137, 92R171, and 92R178 based on the pedigree information of each line. Yr3a and Yr4a were detected in two entries, and four cultivars may contain Yr6. Three cultivars were postulated to possess YrSD, one carried Yr27, and one may possess Yr7. Yr2 was found in combinations with other genes in two lines. Thirty-three genotypes showed slow stripe rusting resistance at two locations in both seasons by Fisher's F-protected least significant difference (LSD) test. The correlation coefficient between relative AUDPC and FDS was very high at the two locations, indicating that FDS could be used as a reliable and simple indicator for evaluation of slow stripe rusting resistance in wheat breeding program.F₁, F₂ and F₃ populations derived from the cross Zhou 8425B/Chinese Spring were inoculated with Chinese PST isolate CYR32 (Tiaozhong 32) in the greenhouse for the identification of seedling resistance gene in Zhou 8425B. A total of 790 SSR primers were used to test the parents as well as resistant and susceptible bulks. The polymorphic SSR markers between the resistant and susceptible bulks were used for genotyping the F₂ and F₃ populations. Linkage analysis was conducted with the software MapManager QTXb20. Results indicated that Zhou 8425B carries a single dominant resistance gene to Chinese PST isolate CYR32, located on chromosome 7BL, temporarily designated YrZH84. The resistance gene YrZH84 was closely linked to the seven SSR loci on the 7BL with genetic distances ranging from 1.4 cM to 12.0 cM. The two closest flanking SSR loci were Xcfa2040-7B and Xbarc32(?)7B with genetic distances of 1.4 cM and 4.8 cM to YrZH84, respectively. At present, stripe rust resistance genes Yr2 and Yr6 have been located to chromosome 7B. Zhou 8425B and the lines carrying Yr2, Yr6 and Yr9 were inoculated with 25 PST isolates in a seedling test. The result showed that reaction patternsof YrZH84 to 25 PST isolates were different from those of Yr2 and Yr6. In addition, the locations of YrZH84, Yr2 and Yr6 are different, suggesting that YrZH84 is probably a new stripe rust resistance gene.