Inheritance And Mapping Of Powdery Mildew Resistance Gene In A Trititrigia Germplasm Line

Wheat powdery mildew caused by Blumeria graminis f. SP. tritici (Bgt) is one of the main diseases of wheat in wheat-producing regions of the world, which seriously constraints on wheat production. So far, more than 60 powdery mildew resistance genes have been identified on different chromosomes or arms, but only several genes were applied successfully in wheat breeding programs. With the large-scale cultivation of resistant varieties, some resistance genes usually become ineffective. Therefore, it is necessary for the ongoing development and identification of new resistance genes. The wild relatives, Thinopyrum intermedium (2n= 42, JJJSJtSt), has a wealth of genetic variation for the improvement of resistance to fungal diseases including powdery mildew in wheat, and some of resistance genes have been widely used in wheat breeding programs.CH09W83 is a homogeneous BC2F5-derived resistant wheat line from ’Jintai 170/TAI7047//2*Jintai 170’, and its resistant parent TAI7047 is a partial amphiploid developed by crossing common wheat cultivars with Th. intermedium accession Z1141 with pedigree’Taiyuan 768/Z1141//Jinchun 5’. To investigate the inheritance of powdery mildew resistance introgressed from Th. intermedium, CH09W83 was crossed to susceptible cultivars Taichang 29 and Jintai 170 to yield segregating populations. The F2, F3 and BC1 were tested for segregation of powdery mildew resistance. An F2 population from Taichang 29/CH09W83 was further used for microsatellite screening and gene mapping.The main results obtained in this study are as follows:(1) Seedlings of Th. intermedium, the resistant parent TAI7047 and CH09W83 as well as all the wheat parents were screened for their reactions to powdery mildew in the greenhouse using seven Chinese Bgt isolates. The disease evaluation showed that the resistance of CH09W83 is effective against all the Bgt isolates tested, including the most widely virulent and predominant pathotypes E09, E20 and E21, whereas the wheat parents Jintai 170, Taiyuan 768 and Jinchun 5 were susceptible. These results demonstrated that CH09W83 conferred resistance to powdery mildew similar to its putative donor TAI7047, and wild parent, suggesting the resistance was probably derived from Th. intermedium and expressed in this wheat line.(2) When somatic cells of the resistant line CH09W83 were probed by genomic DNA of Th. intermedium and blocked with CS genomic DNA, no translocation was visible, suggesting that if a translocation was present in this line, its size was too small to be detected by GISH. Metaphase I chromosome pairing in PMCs of CH09W83 and its hybrids with susceptible wheat genotype Taichung 29 was 21 bivalents. These results suggested that CH09W83 is probably a cryptic wheat-Th. intermedium translocation.(3) When inoculated with isolate E09 at the adult stage, all F1 plants from all crosses showed infection types similar to the susceptible parent, implying that the resistance in CH09W83 was recessive. Segregations of the F2 population from the susceptible/resistant cross and the BC, population were consistent with those expected for segregations at a single locus. When tested with the same race, the F3 lines from Taichang 29/CH09W83 were scored 32 homozygous resistant:62 segregating:39 homozygous susceptible, confirming the single gene segregation. The recessive gene for Pm resistance in CH09W83 was temporarily designated as pmCH83.(4) The parents and 133 F2 plants corresponding to their F3 families from Taichung 29/CH09W83 were further used for screening microsatellite marker to map the resistance gene pmCH83 using bulk segregant analysis (BSA) method. The result demonstrated that pmCH83 was linked to four co-dominant genomic SSR markers, Xgwm193, Xgwm251, Xwmc652 and Xgpw7272, and flanked by Xgwm251 and Xwmc652 at 4.3 and 3.8 cM, respectively. Using the Chinese Spring nullitetrasomic and ditelosomic lines, the polymorphic markers and the resistance gene were assigned to chromosome arm 4BL. As no permanently named powdery mildew resistance genes had been assigned to chromosome 4BL, pmCH83 should be a new gene for resistance to powdery mildew.