| Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most important diseases of common wheat (Triticum aestivum L.) worldwide. Since 1970s, due to more intensive wheat cultivation systems, including the use of semidwarf cultivars,improved irrigation and fertilization conditions, and resistance genes be rapidly overcome, powdery mildew severities have increased in drier and warmer areas as well. Breeding and utilization of resistant cultivars are the most economical and environmentally safe method to decrease fungicide application and to reduce yield reduction due to the disease. Molecualr markers tightly linked to resistance genes not only facilitates the identification and mapping of resistance genes, but also can be used for marker-assisted selection (MAS). MAS greatly enhances the breeding efficiency and expedites the process. In the present study, based on the analysis of the genetic characteristics and origin of the powdery mildew resistance gene in Shannong 030-1, we had constructed the genetic maps of the powdery mildew resistance gene, discussed the application of the tightly linked markers in further study and marker-assisted selection.1. Germplasm line Shannong 030-1 is highly resistant (IT:0;) to powdery mildew prevalent isolate E09 at the seedling and adult plant stages in North China. Genetic analysis using four F1 population and four F2 segregating population, Shannong 030-1/Yannong 15, Shannong 030-1/Kavkaz, Shannong 030-1/Huixianhong and Shannong 030-1/Chancellor, indicated that the segregation ratio resistant individuals and susceptible individuals was 3:1, and a single dominant gene was responsible for the resistance of Shannong 030-1, temporarily designated Pm030-1.2. Chi-square text and PCR profiles with 1RS-specific molecular markers of four F2 segregating population, Shannong 030-1/Yannong 15, Shannong 030-1/Kavkaz, Shannong 030-1/Huixianhong and Shannong 030-1/Chancellor, indicated that the ratio of individuals with specific bands and individuals with no specific bands was not 3:1, and genotype (amplification of specific bands) and performance type (disease resistance) is inconsistent. Correlation analysis was made to explain the correlation between 1RS-specific markers and powdery mildew resistance gene of Shannong 030-1, the results showed they had no correlation. All indicated that the powdery mildew resistance of Shannong 030-1 had nothing to do with rye 1RS chromosome.3. Five specific molecular markers linked to the powdery mildew resistance gene of Shannong 030-1were selected from 2492 G-SSR, EST-SSR and STS markers via the Preferred Small Group (PSG) in Shannong 030-1/Yannong 15 F2. The Pm030-1 was mapped by the linkage analysis of a segregating F2 population. The Pm030-1 was linked to five specific markers (CFE27, Xcfd81, Xcfd266, Xcfd18 and Xcfd25) and their most likely order was CFE27–Xcfd81–Pm–Xcfd266–Xcfd18–Xcfd25 at 3.2, 1.3, 8.6, 24.3 and 24.3 cM, respect- tively. In Shannong 030-1/Kavkaz F2, the Pm030-1 was linked to two specific markers (CFE27 and Xcfd81) and their most likely order was CFE27–Pm–Xcfd81 at 3.7 and 0.9 cM, respectively; In Shannong 030-1/Chancellor F2, the Pm030-1 was linked to two specific markers (Xcfd81 and CFE27) and their most likely order was CFE27–Xcfd81–Pm at 11.3 and 3.0 cM, respectively; In Shannong 030-1/Huixianhong F2, the Pm030-1 was linked to three specific markers (CFE27, Xcfd81 and Xcfd266) and their most likely order was Xcfd266–CFE 27–Pm–Xcfd81 at 13.8, 2.2 and 3.4 cM, respectively. These results indicated that markers Xcfd81 and CFE27 were the tightly linked markers to the Pm030-1.4. The the Pm030-1 was located on chromosome 5D, according to the infection-type of E09 Bgt isolate and mapping results, and we conclude that it might be powdery mildew resistance gene Pm2 or a new allele of the Pm2 locus. The molecular markers developed in this study are useful for marker-assisted selection(MAS) and gene pyramiding of powdery mildew resistance genes in wheat breeding programs. |
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