Evaluation Of Powdery Mildew Resistance And Analysis Of Resistance Genes For Winter Wheat Cultivars In China

Wheat(Triticum aestivum L.)is an important crop in China,which is used in food,fodder and industrial materials.Wheat powdery mildew is one of the most severe epidemic foliar diseases,which affects winer wheat production in the country.Blumeria graminis f.sp.tritici(Bgt),the casual agent of wheat powdery mildew,is a biotrophic fungus,and is distributed throughout the most winter wheat producing regions.The improvement of resistance to powdery mildew in the commercial cultivars is an important objective in the winter wheat breeding programs.The objectives of this study were(1)to understand the status and potential of the disease resistance breeding efforts by the assessments of resistance to powdery mildew and the detection of resistance genes using molecular markers for the wheat entries that were involved in the national yield trials during 2012-2015;(2)to understand the effective application of Pm52 from Liangxing 99 as a parent in breeding programs and the production of wheat by resistant assessment and molecular marker detection of Liangxing 99 and ten wheat cultivars with Liangxing 99;and(3)to localize the gene for resistance to powdery mildew in the wheat cultivar Shannong 20 using the method of BSR-Seq.The main results are described below.1.Eight Bgt isolates from different sources were used to test the seedling responses of an array of 426 winter wheat cultivars from the national yield trials.The resistant frequencies of tested wheat cultivars in the reactions to 8 isolates differed from each other with a range of 13.6-25.4%.Among them,152 cultivars were resistant to at least one isolate,accounting for 35.7%.The proportion of the resistant cultivars in the 129 registered cultivars was less than 30%.The percentage of resistant entries of 66 cultivars from the Northern Winter Wheat Zone was less than 20% when tested with each isolate.More than 50% of cultivars in 66 cultivars from the Southwestern Winter Wheat Zone and 46 cultivars from the Middle and Low Yangtze Winter Wheat Zone were resistant to at least one isolate.Only 19.7% of the cultivars was resistant in the field tests for the two growing seasons at the adult stage;however,the frequency of powdery mildew-resistant cultivars from the Southwestern Winter Wheat Zone was more than 50%.2.The presences of genes Pm8 and Pm21 in the wheat cultivars were detected using the functional marker of Pm8 and the linkage marker of Pm21.Pm8 was present in 36.9% of the cultivars.The frequencies of this gene in the Northern Winter Wheat Zone and the Yellow and Huai Winter Wheat Zone were 50.0% and 44.8%.The frequency of Pm8 also was 41.1% in the commercial cultivars.Pm21 gene was discovered in 15 cultivars,inlcuding 11 cultivars from the Southwestern Winter Wheat Zone,3 cultivars from the Middle and Low Yangtze Winter Wheat Zone and one cultivar from the Huang and Huai Winter Wheat Zone.This gene was not detected in the cultivars from the Northern Winter Wheat Zone.3.Liangxing 99 is a powdery mildew-resistant winter wheat cultivar adapted to the Yellow–Huai Rivers Valley Facultative Wheat zone and the Northern Winter Wheat Zone.Its powdery mildew resistance is conferred by gene Pm52 on chromosome 2BL.A total of 123 isolates of Blumeria graminis f.sp.tritici collected from different wheat producing regions were used in assessment of disease resistance,and Liangxing 99 was resistant to 80% of them.During the four consecutive growing seasons from 2013 to 2016,Liangxing 99 was immune or highly resistant to the mixture of Bgt isolate inoculated at the adult plant stage.A gene-specific marker Xgwm120 closedly linked to Pm52 and 27 Bgt isolates were used to analyze ten wheat cultivars with Liangxing 99 as a parent.Heng 4568,Hannong 2312,Zhongxinmai 99 and DH51302 may inherit Pm52 from Liangxing 99,while the powdery mildew resistance genes of Zhengmai 369 and Jimai 729 may differ from Pm52.Shi U09-4366,XR4429,Heng 10-5039 and Nongda 3486 were susceptible to all the Bgt isolates examined and did not carry gene Pm52.The responses of these cultivars at the adult plant stage were consistent with those at the seedling stage.4.Winter wheat cultivar Shannong 20 was strongly resistant to powdery mildew at the seedling and the adult plant stages.Based on the genetic analysis of resistance using F1,F2 and F2:3 populations derived from the cross Shannong 20 × Han 4564,a dominant gene,tentatively designated PmSN20,was detected using the Bgt isolate E20.By means of BSR-Seq method,PmSN20 was located in locus Pm2 on wheat chromosome 5DS.Results of sequence alignment indicated that the nucleotide sequences of PmSN20 and Pm2 were identical,which confirms that they are the same gene.The virulence pattern of PmSN20 was similar to Pm2 when tested with 38 Bgt isolates.