Mapping Of Resistance Genes Against Stripe Rust And Powdery Mildew In Common Wheat (Triticum Aestivum L.)

Stripe rust and powdery mildew, caused by Puccinia striiformis f. sp. tirtici and Blumeria graminis f. sp. tritici, respectively, are the most damaging diseases in common wheat (Triticum aestivum L). Breeding and utilization of resistant varieties are the most economical and effective way to control the disease. After the emergence of the highly virulent race CYR32 of Puccinia striiformis f. sp. tirtici and highly virulent isolate E20 of Blumeria graminis f. sp. tritici, most of Chinese wheat varieties have lost their resistance to stripe rust and powdery mildew, and thus vulnerable to the two diseases under suitable climate. Therefore, identification of stripe rust and powdery mildew resistance genes are essential for breeding resistant wheat cultivars.The objectives of this study were to identify the molecule markers tightly linked to wheat stripe rust resistance gene YrZH84 employing the resistance gene-analog polymorphism (RGAP) markers, and validate the availability of the markers, and to map the powdery mildew resistance gene in Jimai 22. The molecular markers identified in this study can be used for marker-assisted selection in wheat breeding. The results are summarized as follows:1. A total of 522 F2 plants derived from the cross Zhou 8425B/Chinese Spring and their parents were used for linkage analysis. In all, 1711 RGA primer combinations were used to test the parents, as well as the resistant and susceptible bulks. Of the 116 RGA primer combinations, 40 generated repeatable and clearly polymorphic bands between the resistant and susceptible bulks. One RGAP marker, designated Xrga-1, showed a tight linkage with the stripe rust resistance gene YrZH84, with a genetic distance of 0.8 cM. The DNA sequence of the RGA fragment was in a size of 343 bp. BLAST analysis indicated that the Rpg1 showed 93% of identical nucleotide sequences to that of barley stem rust resistance gene Rpg1, and 92% to that of barley powdery mildew resistance gene Mla homology family. These results will greatly benefit for the marker-assisted selection and cloning of the resistance gene YrZH84.2. Forty-eight varieties derived from Zhou 8425B and seven important commercial varieties from the Huang and Huai winter wheat region were tested by the YrZH84 flanking RGAP marker Xrga-1 and SSR marker Xcfa2040. The results indicated that the specific 343-bp PCR fragment generated by the Xrga-1 and 238-bp by Xcfa2040 were detected in 10 varieties, i.e. Zhoumai 11, Zhoumai 17, Zhoumai 20, Zhoumai 22, Aikang 58, 04 Zhong 36, Yuanyu 3, 05 Zhong 37, Yuankang 18 and Yuzhan 10, which showed resistant to the prevalent race CYR32 of Puccinia striiformis f. sp. tirtici and should contain the stripe rust resistance gene YrZH84 based on resistance identification result and the pedigree analysis. In contrast, the other 38 derivatives of Zhou 8425B, susceptible to the race CYR32, did not amplify the corresponding specific PCR fragment, indicating that the resistance gene YrZH84 were lost during the development of these varieties. These results showed that the marker Xrga-1 and Xcfa2040 can be effectively used for the test of the stripe rust resistance gene YrZH84 and marker-assisted selection.3. A total of 228 F2 plants and 99 F2;3 lines derived from the cross Jimai 22/Chinese Spring and their parents were used for the identification of powdery mildew resistance gene in the Jimai 22 using a highly virulent isolate E20 of Blumeria graminis f. sp. tritici, and SSR and EST markers. The result showed that Jimai 22 carried a dominant powdery mildew resistance gene, designated PmJM22 tentatively. Pedigree analysis and resistance test indicated that this gene may be originated from an English common wheat line TJB 259/87. Molecular marker analysis indicated that the powdery mildew resistance gene PmJM22 was mapped on chromosome 2BL, and linked to SSR marker Xwmc149-2B and EST markers CD490485-2B with genetic distances of 7.7 cM and 18.7 cM, respectively. Based on the origins, chromosome locations and reaction patterns of the powdery mildew resistance genes on chromosome 2BL, PmJM22 is likely a new powdery resistance gene that is different from Pm6, Pm26, Pm33 and MlZec1.4. Seventy-nine advanced wheat lines participating in the national field trials for the Huang Huai winter wheat region and two control varieties in 2008-2009 cropping season, and seven important commercial varirties were used for seedling test to the isolate E20. The results showed that 4 lines were resistant to E20, accounted for 5.1%, in which Yunong 209, Yuan 594 and Jinhe 9123 were highly resistant and Luomai 27 moderately resistant, whereas 75 were susceptible to E20 with a percentage of 94.9%, including 22 moderately susceptible and 53 highly susceptibile lines. Two control varieties Zhoumai 18 and Yanzhan 4110 were moderately susceptibile to E20. Three of the seven commercial varirties were highly resistant, i.e., Zhoumai 22, Jimai 22 and Aikang 58, and Han 6172 were moderately susceptibile, while Xinmai 18, Jimai 19 and Shi 4185 were highly susceptibile. Pedigree analysis indicated that the genetic basis of these new breeding lines was rather narrow, and thus it is essential to find some new powdery resistance genes for the development of resistant wheat varieties.