Genetic Analysis And QTL Mapping Of Wheat Resistance To Bipolaris Sorokiniana Black Point Based On RIL Population

Black point of wheat occurs in many countries in the world,and it is increasing in the Yellow and Huai wheat areas of China in the recent years.This disease is harmful to the appearance and processing quality of wheat grains,and also reduces the germination rate,seedling emergence rate and seed vigor.Planting resistant wheat cultivars is an effective way to control black point.It is important to explore the genetic loci for black point resistance and to develop molecular markers ued to assist selection for breeding wheat cultivars resistant to black point.In this study,196 recombinant inbred lines(RIL)at F7,derived the cross using susceptible line "PZSCL 6" as female parent and resistant line “Yuyou 1” as male parent,were planted in four environments at three locations in 2020 and 2021(just Xingyang in 2020).Resistance identification of RILs was carried out under the inoculation condition of isolate Ta-BP33 of Bipolaris sorokiniana(the dominant pathogen causing black point in Henan province),using the method of spraying spore suspension and bagging for moisture at 10 days after anthesis.,Based on the incidence at four environments,genetic analysis of wheat black point resistance was conducted,and 25 resistant and 25 susceptible inbred lines were selected to construct mixed pools for bulk segregation analysis(BSA)combining wheat 660 K SNP array.Polymorphic SSR markers and d CAPS markers independently developed were seleted to construct a genetic linkage map of the RIL population,and QTL mapping for black point resistance was carried out based on the incidence at four environments.The main results of this study are as follows:1.Under the inoculation condition of B.sorokiniana,the black point incidence among the RIL populations ranged from 1.1% to 68.0%,with an average of 26.2%,and that of resistant parent was 10.7%,while susceptible parent was 54.9%.The incidence was continuously distributed in all four environments,and there was hyperparental separation in both resistant and susceptible inbred lines.The black point incidence was significantly correlated among different environments(r = 0.622~0.911).Based on the results of genetic analysis using mixed inheritance model of major genes plus polygenes,black point in the RIL population was in accordance with “additive epistatic inheritance model of two main genes”,and heritability of the main genes is 51.4%~67.9%.2.A total of 184 SNP markers associated with black point resistance were detected through BSA,which located on 15 chromosomes.The most SNP was detected on chromosome 5A and 5B,41 and 34 each,followed by chromosome 4B and 2A,22 and19,respectively,which suggesting there is important loci for black point resistance on chromosome 5A,5B,4B and 2A.Then SNP markers on four chromosomes were developed to d CAPS markers,and 7 polymorphic d CAPS markers were seleted,which together with polymorphic SSR markers were used for QTL mapping.These 184 SNPS belong to 45 loci associated with black point resistance,among which 21 were new resistance loci detected in this study.3.Six QTL for B.sorokiniana black point resistance were detected on chromosomes 2A(1),5A(1),5B(2)and 5D(2),respectively,based on the phenotypic data at four environments and genotypes of 152 polymorphic SSR and d CAPS markers,which were designated as QBB.hau-2A,QBB.hau-5A,QBB.hau-5B.1,QBB.hau-5B.2,QBB.hau-5D.1and QBB.hau-5D.2,respectively.All the resistance alleles of the six QTL were derived from the resistant parent “Yuyou 1”.In particular,QBB.hau-5A and QBB.hau-5D.1 detected in three environments and with large effect(> 11.3%),could be two major QTL.QBB.hau-5D.1 detected by our group is likely to be a new locus for black point resistance.4.Resistance effects of QBB.hau-5A and QBB.hau-5D.1 was analyzed in the RIL population using their linked markers Xwmc654 and Xgwm174,respectively.Black point incidence in inbred lines with both QTL was the lowest(18.7%),which was significantly lower than that of the lines without two QTL(33.5%),and that of the lines with only one QTL(24.4%-26.9%).Incidence of the lines with one QTL(QBB.hau-5A or QBB.hau-5D.1)was also significantly lower than that of the lines without two QTL.The results implied that black point incidence could be effectively reduced by transferring these QTL to high-yielding wheat cultivars.