Genetic Analysis Of Black Point Resistance In Common Wheat (Triticum Aestivum L.)

Black point disease can significantly downgrade wheat processing and nutrition quality and result in significant economic loss to wheat industry.Although several biological and chemical strategies have been used to control black point,breeding resistant cultivars is still the most effective,economic and environment-friendly approach.Thus,it is necessary to select resistant cultivars and identify molecular markers tightly linkaged or significantly associated with black point resistance to facilitate resistance breeding.Consequently,the aims of this study were to(1)investigate the causual of black point disease,(2)identify loci and candidate genes for black point resistance by linkage analysis and genome-wide association study(GWAS),and(3)explore new single nucleotide polymorphisms(SNPs)variations and different expression genes(DEGs)by RNA-sequencing(RNA-Seq).The main results were summarized as follows:1.Although one fungal species Altemaria altemata from the black point grains was isolated from the infected tissue,the follow-up verification showed that this kind of fungus could not lead to a significant increase of black point reaction.Black point could be triggered when spikes were exposed to high humidity during grain filling period,both in the greenhouse and in the field.In addition,the activity of POD(Peroxidase)and PPO(Polyphenol oxidase)in susceptible cultivars is higher than that in the resistant ones.2.The recombinant inbred line(RIL)population derived from a cross between Linmai 2 and Zhong 892 were genotyped by the wheat 90K iSelect SNP array and were evaluated for black point reaction during the 2011-2012,2012-2013 and 2013-2014 cropping seasons.A total of 6793 SNP markers were used for construction of a high-density linkage map,which covered 2918.4 cM.Composite interval mapping(cCIM)detected nine quantitative trait loci(QTL)on chromosomes 2AL,2BL,3AL,3BL,5AS,6A,7AL(2)and 7BS,explaining 3.7-13.4%of the phenotypic variances.Compared with previous studies,QBp.caas-2BL,QBp.caas-3BL,QBp.caas-5AS,QBp.caas-6A,QBp.caas-7AL.1,QBp.caas-7AL.2 and QBp.caas-7BS are probably new loci for black point resistance.Three candidate genes for black point resistance were identified by BLAST of common wheat and its related cereal genomes with sequences of tightly linked SNPs.3.To better understand the genetic mechanism of black point resistance and identify associated molecular markers,we performed a GWAS using 166 accessions from the Yellow and Huai River valley wheat region and 90 accessions from the Northern winter wheat region,respectively.Thirty-seven unique loci,each explaining 7.9-23.1%of phenotypic variances,were identified on chromosomes 1A(2),2A(2),2B,3A(2),3B(4),3D,4A,4B(2),5A(3),5B(3),6A(2),6B,6D,7A(6),7B(2)and 7D(3),respectively.Among which,five loci were identified in both association panels,19 were stably detected in two or more environments,seven were coincident with the known genes or QTL,whereas the other 30 were likely to be novel loci.In silico analysis of sequences of significantly associated SNPs identified eight candidate genes associated with black point resistance,which involved in peroxisome synthesis,plant hormone signal transduction and stress resistance.4.A total of 139 new SNP variations were identified in the confidence interval of the QTL for black point resistance detected in the Linmai 2/Zhong 892 RIL population by RNA-Seq approach,multiple candidate genes involved in peroxisome biosynthesis,phenolics metabolism and plant hormone signal transduction,which maybe work collaboratively in the formation of black point.