Analysis Of Wheat Mutants With Enhanced FHB Resistance And Mapping The Causal Loci

Fusarium head blight(FHB),a serious disease threatening wheat safety production,causes grain shrinkage,grain weight reduction and DON accumulation in grains.With the intensification of greenhouse effect all over the world and the change of cultivation system,the incidence of the disease has been more and more frequent,which undoubtedly brings a great threat to wheat production in China.Wheat FHB resistance is a complex quantitative trait regulated by multiple minor genes.Breeding resistant varieties is the most effective strategy to control FHB from the source,and identification and use of effective resistance genes could accelerate development of varieties resistant to FHB.The wheat variety Ning7840 carries the major resistance QTL Fhb1 and shows moderate to high resistance to FHB.The average percentage of symptomatic spikelets(PSS)ranged from 5%to 20%.The Co60 radiatied mutants of Ning7840 were inoculated with Fusarium graminearum(F.g)and one of mutants(R227)consistently showed significantly stronger resistance to FHB than the wild type did,and only the inoculated spikelet had FHB symptom using single floret inoculation method,and no DON was detected in the grains.In this study,the differences between R227,its wild type and the susceptible reference line S127 with elite agronomic traits were analyzed from the aspects of FHB resistance,agronomic yield characters,anatomical structure,and the relationship between FHB resistance and agronomic traits in a segregating population.Bulked segregant RNA-sequencing(BSR)strategy was used to map the causal SNPs responsible for the enhanced FHB resistance.These conclusions are summarized as follows:Comparisons of the changes in spikelet characteristics,rachilla and infected grains among R227,its wild type Ning7840 and the FHB-susceptible line S127 at different stages after inoculation with F.g indicated that there were significant correlations between PSS,vascular bundle structure destruction and grain damage.R227 consistently showed an enhanced resistance to FHB when compared with wild type Ning7840 at PSS,destruction of vascular bundle structure and grain damage.However,the agronomic and yield characters such as plant type and grain shape of R227 were inferior to those of the susceptible reference line S127.To understand whether there was a pleiotropic effect or independent inheritance for FHB resistance and agronomic traits in R227,S127 and R227 were crossed to generate an F2:3 segregating population(H15).The results showed that there was no significant correlations between them,indicating good FHB resistance and elite agronimic traits can be combined.Mahalanobis distance between the lines in H15 population and the reference line S127 on the phenotypic traits,combined with the PSS,showed that the agronomic yield traits of the lines H15-13,H15-21,H15-33 and H5-34 were simillar to S127 but all of them carried Fhbl and had lower disease severity less than 0.25,indicating good FHB resistance and elite agronomic and yield performance could be combined.In order to map the causal loci responsible for the enhanced FHB resistance for R227,we selected lines without Fhbl but showing FHB resistance in the H15 population for BSA-seq.The extremely resistant and susceptible individuals were inoculated with mung bean soup(mock)and F.g,respectively.The RNA samples of the inoculated spikelets and the neibouring tissues were harvested at 72 hours after inoculation,and the transcripts from both the resistant and the susceptible pools were sequenced to screen the SNPs associated with FHB resistance.About 25%of the SNPs were verified to be genuine,which were located on 2D,2B and 4A,and the SNPs on 2D coincided with the known QTL interval for FHB resistance in Ning 7840,while the SNPs on 2B and 4A have not been reported in Ning7840,and may be causal loci responsible for the enhanced FHB resistance.Part of associated SNPs were transformed into CAPS/dCAPS markers,which could be used as diagnostic markers for the potentially novel QTL.GO analysis of differentially expressed genes showed that nutrient storage protein activity,?-amylase activity and ?-amylase inhibitor activity were differentially enriched between the resistant and the susceptible materials.In the KEGG analysis showed that the differentially expressed genes were involved in phenylpropanoid biosynthesis,glutathione metabolism,plant hormone signal transduction and plant-pathogen interaction.The research results above are of great significance for subsequent fine mapping of the causal loci for enhanced FHB resistance in R227,identification of candidate genes and understanding the resistance mechanism.Since there was no significant correlations between FHB resistance and agronomic yield traits,Fhbl and the QTL on 2D,2B and 4A can be combined with elite agronomic traits using marker-assisted selection to develop elite cultivars.