QTL Mapping For Adult-plant Resistance To Powdery Mildew In Chinese Bread Wheat Founder Parent Zhou8425B

Powdery mildew,caused by Blumeria graminis f.sp.tritici(Bgt),is a severe fungal disease to threaten wheat(Triticum aestivum L.)production in China,resulting in over 300,000 tons of yield loss annually.Therefore,with the help of the booming molecular marker technology to simplify the markerassisted selection(MAS),we can accelerate the resistance breeding process to reduce yield loss caused by powdery mildew more efficiently and greenly to ensure the national food security.Zhou8425 B is a founder wheat line widely used as a parent in Chinese wheat breeding programs,particularly in Henan province.Identification of genes for adult-plant resistance(APR)to powdery mildew in Zhou8425 B is of great importance for controlling the disease.In the present study,243 RILs derived from the cross of Zhou8425B/Chinese Spring were planted in Beijng and Zhengzhou during 2014-2015 and 2015-2016 cropping seasons.Field trials were carried out in randomized complete blocks with three replicates in each environment.A total of 85 commercial wheat cultivars derived from Zhou8425 B for QTL velidation were grown in Beijing,Zhengzhou and Xingyang in the 2016-2017 cropping season.Wheat seedlings were inoculated with the prevailing Bgt isolates E09 and E20.The high-density Illumina wheat 90 K iSelect SNP array was used to map QTL for APR to powdery mildew in 243 RILs.The main results are summarized below:1.QTL mapping for adult-plant resistance to powdery mildew in Zhou8425BBased on the phenotyping data from four environments and high-density linkage map in the RIL population of Zhou8425B/Chinese Spring,inclusive composite interval mapping(ICIM)identified four QTL on chromosomes 1BL,3BS,4BL and 7DS,designated as QPm.caas-1BL.1,QPm.caas-3BS,QPm.caas-4BL.2 and QPm.caas-7DS,respectively.Resistance alleles at the QPm.caas-1BL.1,QPm.caas-3BS and QPm.caas-4BL.2 loci were contributed by Zhou8425 B,whereas that at QPm.caas-7DS was from Chinese Spring.QPm.caas-3BS,likely to be a new APR gene for powdery mildew resistance,was stably detected in all four environments.2.The validation of QPm.caas-3BS in 85 Zhou8425 B derivativesOne single nucleotide polymorphism(SNP)marker closely linked to QPm.caas-3BS was transferred into a kompetitive allele-specific PCR(KASP)marker and a semi-thermal asymmetric reverse PCR(STARP)marker.Among 85 Zhou8425 B derivatives,44 possessed the resistance allele at the QPm.caas-3BS locus based on the test of KASP and STARP markers.Cultivars with the resistance allele at the QPm.caas-3BS locus had a reduced maximum disease severity(MDS)by 7.1 % on average.The KASP and STARP markers can be used for MAS in improvement of powdery mildew resistance in wheat breeding.