Genetic Dissection Of Root Morphology And Drought-tolerant Related Physiological Traits In Wheat (Triticum Aestivum L.)

Wheat(Triticum aestivum L.)is one of the three major cereal crops mainly distributed in arid and semi-arid regions,to reduce the negative effect of drought stress on its production and quality,large amounts of agricultural water had been used each year.Breeding drought-tolerant wheat varieties is an essential strategy to ensure food and water resources security in our country,choosing elite parental lines and their progenies' traits is the key to promote the improvement of drought tolerance in wheat.The abilities of physiological regulation and water uptake by root determin the drought tolerance of wheat,however,the evaluation of related physiological and root traits is labour intensive and time consuming,which is limited by environmental factors and identification methods.Therefore,dissecting the genetic basis of root morphology and drought-tolerant related physiological traits,and developing molecular marker can provide strong support for efficient improvement of drought-tolerance in wheat.In the present study,root traits of a natural population(323 wheat accessions)and a doubled haploid(DH)population were investigated at seedling,tillering,booting and mid-grain filling stages,and physiological and yield traits were measured under two water regimes,i.e.well-watered and drought stress(rain-fed);accessions with drought tolerance were selected;with a wheat 660 K SNP array,the genetic basis of physiological and root traits related to drought tolerance were dissected.The main results were as follows:1.Twenty-eight accessions with high drought tolerance at seedling stage were selected by repeated drought-stress method,nine accessions with high drought tolerance at adult stage were selected by direct identification in field;21 accessions showed drought tolerance or high drought tolerance at both seedling and adult stages.2.The correlation analysis results indicated that drought tolerance at seedling stage is positively correlated with root dry weight,drought tolerance at adult stage is positively correlated with NDVI(Normalized difference vegetation index),chlorophyll content and root depth,but negatively correlated with CT(Canopy temperature).Root depth is negatively correlated with CT at different growth stages.3.The dynamic analysis for root traits indicated that from germinating to tillering stage is a critical period for the growth of root depth.From tillering to booting stage is a critical period for the growth of root dry weight,booting to mid-grain filling stage is critical period for significant difference of root traits among different wheat accessions.In addition,no significant correlation was detected between root traits at early growth stages(from seedling to tillering stage)and late growth stages(from booting to mid-grain filling stage).4.A genetic map was constructed,which included 30 linkage groups,spanned 4082.4 cM,with an average interval distance of 2.2 cM.5.For genetic dissection of physiological traits related to drought tolerance,86 and 190 associated loci were identified by linkage mapping and GWAS(Genome-wide association study),respectively,17 and 24 loci showed pleiotropy,of which QPT52,LPT40,LPT41,LPT101 and LPT180 were associated with all three physiological traits(CT,NDVI and SPAD);11 co-located loci were identified by combining the results of linkage mapping and GWAS.6.For genetic dissection of root traits,24 and 63 associated loci were identified by linkage mapping and GWAS,respectively,5 and 7 loci showed pleiotropy,3 co-located loci were identified by combining the results of linkage mapping and GWAS.7.The genetic correlation analysis between physiological and root traits showed that 17 loci were co-located,and the loci related to root depth were all related to CT.Of which,LRT44,LRT50 and LRT54 were stably identified at different growth stages.The results of gene prediction and minirhizotron system scanning suggested that high-affinity nitrate transporters genes(NRT2)are the candidate genes in LRT44,LRT50 and LRT54.The present study genetically dissected physiological and root traits associated with drought tolerance in wheat.These results provide theoretical bases and technical supports for wheat improvement by molecular technologies.