Association Mapping For Physiological And Agronomic Traits Related To Drought Tolerance In Wheat

The drought resistance of wheat, as a complex quantitative trait, is controlledby polygenes. Further researches on molecular quantitative genetics haveprogressively better uncovered mechanisms of complex quantitative traits related todrought resistance in wheat. Association analysis by wheat natural population candirectly make insight into significant markers associated with phenotypic variation. Inthis study,120accessions with different characteristics of drought resistance wereselected as experimental materials from different ecological regions to analyze geneticdiversities and genetic structure by SSR markers. Whilst association analysis wasperformed between SSR and phenotype of physiological traits (flag leaf chlorophyllcontent (SPAD), air-canopy temperature difference (CTD)) and agronomic traits(Heading date (HD), Flowering date (FD), flag leaf length (FLL), flag leaf width(FLW), plant height (PH) and thousand-grain weight (TGW)) under different waterenvironments. The object was to mine associated SSR markers with target traits, andprovide theoretical basis for genetic improvement of wheat drought resistance. Theresults are as follows:(1) Total of98polymorphic SSR markers were identified in the naturalpopulation in wheat. Each chromosome was covered2-10SSR loci. The variationfrequency of alleles was ranged from0.295to0.312. The polymorphism informationcontent (PIC) was varied from0.275to0.747. Among them, the PIC value was higheras0.747on chromosome2B, while that was lower as0.275on chromosome4A.Moreover, a positive correlation was greatly significant (r=0.75, P<0.01) betweenthe number of allelic variation and PIC value.(2) The genotypes of the natural population in wheat were clustered fourgroups by genotyping analysis with SSR. Wheat cultivars (lines) derived from sameor similar ecological regions were grouped together. GroupⅠ contained59cultivars(lines) mainly from Gansu. Twenty three cultivars in group Ⅱ were belonged toShanxi and Beijing. Ten cultivars in Group Ⅲ were derived from Shandong, Henanand Gansu. And, Group Ⅳ included28cultivars were almost from the United Statesand CIMMITY.(3) All target traits of physiology and agronomy were sensitive to water environments. Their phenotypic variations was extensive with low heritability(hB2=0.32～0.79). Phenotypic correlations showed generally lower (r=0.031～0.556**)among target traits, indicating that these target traits were essentially subjected tocomplex quantitative genetic regulated by minor-effect polygenes.(4) Eight and five SSR markers were identified with significant association forthe chlorophyll content of flag leaf and the air-canopy temperature difference underdifferent water environments, respectively. These makers were mainly distributed onsuch chromosomes as1D,2A,2B,2D,3A,3B,3D,4B,5D,7A and7B. As a result,Xwmc53(3B), Xgwm182(5D), Xgwm501(2B), Xgwm679(3A) and Xwmc441(2B)showed highly significant association with the chlorophyll content of flag leaf.Similarly, Xwmc317(2B), Xgwm261(D) and Xgwm471(7A) were highly significantlycorrelated with the air-canopy temperature difference. Not any SSR was significantlyassociated with the chlorophyll content of flag leaf and the air-canopy temperaturedifference at the same time under different water environments, while some SSRmarkers closely associated these two traits were distributed on the same chromosome.(5) Under different water environments, it was identified14,6,8,4,4and8SSR markers significantly associated with six traits related to agronomy, such asflowering date, heading date, flag leaf length, flag leaf width, plant height andthousand-grain weight, respectively. These SSR markers were mainly distributed on17chromosomes of wheat except1D,4A,6D and7D. Twenty-one of these significantSSR markers were detected under the drought stress. Xgwm499(5B) and Xgwm291(5A) showed highly significant correlation with plant height and thousand-grainweight. Meanwhile, Xgwm499(5B) was also highly significantly associated with leaflength under the drought stress. Under the well-watered and drought conditions, totalof44SSR markers were detected with significant correlation with some traits, mainlydistributed on chromosomes1B,2A,2B,2D,3A,3B,5A,5B,5D,6A,7A and7B. TheseSSR markers would be made great importance in the marker-assisted selection and thegenetic improvement in drought tolerance in wheat.