Reactions Of Chinese Wheat Cultivars To Powdery Mildew And Molecular Detection Of Resistance Genes

Powdery mildew caused by Blumria graminis f. sp. tritici is one of the most devastating diseases of wheat. The race-specific resistance genes commonly used are often overcome by new pathogen races possessing corresponding virulence genes. Discovery of new resistance genes and development of resistance to powdery mildew has proven to be the most safe and effective means to control the disease. In the present study, the virulence patterns of 10 isolates of Blumeria graminis f. sp. tritici were identified, seedling- and adult-plant reactions of Chinese wheat cultivars to different isolates were analyzed, and molecular markers associated with powdery mildew resistance genes were used to detect resistance genes in these cultivars.According to the virulence patterns of the 10 isolates, isolate E20 was considered to be the most virulent isolate and only 9 cultivars with known resistance genes were virulent on the isolate. The cultivars possessing genes Pm13, Pm21, Pm24, and Pm5+6 were highly effective against the 10 isolates tested.The reactions of 130 nationally approved wheat cultivars released during the past 30 years to 8 isolates were tested. The frequencies of the cultivars against the strong virulence isolates E20, E23, and Bg5 were 5.7%,9.8%, and 11.9%. For the weak virulence of Bg2 (from Henan Province) and Bg4 (from Hubei Province), the virulent frequencies were 25.6% and 35.2%, respectively. The frequencies of the cultivars against isolates E05, E09, and Bgl (from Hebei Province) were 15.0%,16.3%, and 18.2%, respectively.Comparison of powdery mildew resistance in the 130 commercial cultivars indicated that most cultivars released in the 1980s were susceptible. The frequencies of resistant cultivars released in the 1990s against different powdery mildew isolates ranged from 0%(E23) to 37.9%(Bg4). The frequencies of resistant cultivars released in the last decade ranged from 8.8% to 38.6%, which indicated that the resistance of the cultivars were improved. The analysis of molecular marker linked to the resistant genes suggested that three cultivars may possess resistance gene Pm4a, two cultivars may contain Pm21, and the frequency of Pm8 was 46.1%. The results of 2008-2009 Huanghuai wheat cultivar regional test indicated that powdery mildew resistance in the cultivars of the South Huanghuai Region was better than the North. Cultivars with gene Pm8 in the cultivars tested accounted for an average of 57.1%. The proportions of winter wheat group and spring wheat group in the south region were 60.9% and 66.7%, respectively. In the north region, the frequencies of gene Pm8 in the two groups of the north were 50%. Gene Pm21 was detected only in a few cultivars in the south region of winter wheat group B.Seedling reactions of wheat core collection comprising of 262 cultivars to isolates E09, Bg4, Bg1, Bg2, E20, Bg5, and E23 showed that the proportions of susceptible cultivars were 3.2%,12.16%,10.53%,7.98%,4.98%,12.31%, and 3.1%, respectively. The analysis of the resistance genes with gene-specific markers indicated that Pm8 was present in 12 improved cultivars, and Pm4a was detected in 3 cultivars. In the adult-plant reaction test,51 cultivars showed resistant reactions among 716 cultivars or lines tested.Two emmer and five wild emmer wheats were high resistant or immune to all the isolates. The detection of resistance genes suggested that the diagnostic fragments specific for Pm16 were amplified in a few accessions. Some wild emmer wheats that were highly resistant to powdery mildew isolates tested produced no specific amplification the markers specific for Pm3,Pm4a,Pm16,Pm21,Pm5e,MlWE27,PmDr147å’ŒIW72. This indicated that these accessions may have resistance genes that were different from the known genes tested.