Genetic Mapping Of Susceptible Gene(s) From A Wheat Mutant Susceptible To FHB

Fusarium head blight(FHB)is a fungal disease caused by Fusarium species complex.FHB resistance is a quantitative trait controlled by genes,and FHB phenotype is affected by environmental cues such as temperature and humidity.It is of great significance to explore and utilize QTL for resistance and susceptibility to FHB for understanding resistance mechanism and for breeding resistant varieties.The wheat variety Ning 7840 is an FHB resistant variety carrying Fhb1.In the previous work of our laboratory,we obtained a mutant susceptible to FHB by EMS mutation of Ning 7840,and crossed it with its wild type to develop a recombinant inbred line(RIL)population by single seed descendant method.In this study,we inoculated the RIL population with F.g.inoculum for two years,and the percentage of diseased spikelets(PSS)was scored and DON content in grains was determined.In order to identify the causal mutation sites for the susceptibility,we selected the highly resistant and highly susceptible varieties in the RIL population and inoculated them with green bean soup(control)and F.g.inoculum respectively.After 72 hours of inoculation,we extracted RNA from the inoculated spikelets and adjacent nodes flanking the inoculated spikelets,and the bulked RNA pools from the lines with contrasting FHB phenotypes were sequenced.Then we selected SNPs associated with FHB resistance in the RIL population.The results showed that:The PSS of the RIL population was significantly positively correlated across two years.The PSS of the susceptible mutant was significantly higher than that of the wild type Ning 7840.DON content in grains was determined by LC-MS.There was a significant difference in DON content between highly resistant and highly susceptible lines,and there was a significant positive correlation between the PSS and DON content.Transcriptome sequencing and signal pathway analysis indicated that the signal pathway of pathogen response overlapped with the signal pathway caused by gene mutation in the mutant,indicating that the mutation of the causal gene(s)in the wild type may cause the mutant to lose the ability to respond to the pathogen.We identifed the SNPs that were significantly associated with resistance to FHB.At the same time,we transformed SNPs into dCAPS marker,DRnaN98dC20,and the causal SNPs were assigned to an interval of 8Mb between 607.34Mb and 615.49Mb on wheat 3DL chromosome.This locus was different from the reported QTL,and it might be a novel locus for regulating FHB resistance.Since both wild-type and susceptible mutants carry Fhb1,we speculated that the susceptible gene in the mutant may be Fhb1 inhibitor or key susceptible factor in the signal pathway.Previous studies were mainly on FHB resistance genes,and only a few on susceptible genes.The results of this study would be useful for subsequent fine mapping and cloning of the causal gene,and understanding of the mechanism underlying FHB resistance.