| Drought is one of the important abiotic stress factors restricting wheat yield. To explore the geneticbasis of drought related complex quantitative traits in wheat play important roles for the geneticimprovement of wheat drought tolerance. In this study, a wheat introgression lines (IL) generated formrepeat backcross [(Jinmai47×Xifeng20)×Jinmai47](BC3F4) were used as plant materials. Thewheat drought-tolerant traits, including plant height (PH), peduncle length (PL), spike per plant (SPP),spike length (SL), total spikelet per plant (TSP), gain number per plant (GNP), spikelet per main spike(SMS), gain number per main spike (GMS), thousand-grain weight (TGW), and grain yield (GY), andphysiological traits, such as chlorophyll content (ChlC), canopy temperature (CT), canopy temperaturedepression (CTD), flag leaf length (FLL), flag leaf width (FLW), rate of excised-leaf water loss (RWL)and relative water content (RWC), were identified under different water conditions by SSR molecularmarkers. QTL for these complicated traits were mapped to discover the genetic basis inheritance andQTL expression pattern. The results were shown as follow:1. Total of949SSR markers were used to analyze the polymorphism between Jinmai47and Xifeng20. Of all191SSR markers showed polymorphism, which reached20.13%of effective amplificationreaction.11of the191markers were detected multi-locus but could not be exactly mapped to geneticlinkage map. The genetic background of Jinmai47was93.5%in this IL by genotype detection.According to the international wheat consensus SSR map,180markers were mapped in the linkage mapof the IL.104makers among the total180markers presented one introgressed line at least, accountedfor57.8%of polymorphic markers. The amount of polymorphic markers ranged from5to15in eachchromosome. And every chromosome contained8.6markers in average. The average length betweentwo markers was14.23cM. The chromosome4A contained15markers, while the3D were only5markers.2. The IL phenotypes of wheat yield associated traits were prone to recurrent parent Jinmai47indifferent water conditions. The genetic diversity index ranged from0.74to0.97, which indicated a widediversity. And transgressive segregation were detected in the IL as well. All the traits were sensitive towater, which presented higher phenotype value in well watered condition than in water stress condition.The traits PH, PL and TGW had higher heritability (h2B=0.48～0.81) compared with other traits. Eachtraits presented positive correlation in different levels. Especially the TGW and PH had strongcorrelation and higher relation degree with GY in drought tolerance indicating the important meaning ofhigh PH and TGW for wheat yield formation. The trait ChlC of IL and their parents presented higherphenotype value in well watered condition than in water stress condition in all growth periods. Andduring flowering stage, ChlC had significant or highly significant positive correlation with GY. In waterstress condition, the phenotype value of FLW were significantly less than in well watered condition,which demonstrated that wheat could reduce the moisture transpiration by narrowing the leaf widthduring drought stress.3. Of all35additive QTLs (A-QTLs) and66epistasis QTLs (AA-QTLs) controlled yield traitswere detected in the IL, distributed in all chromosomes except3A. The A-QTLs controlling2or moretraits were located next to the markers Xwmc332(2B), Xgwm261(2D), Xgwm759(5B), and Xgwm400(7B). AA-QTLs controlling3or more traits were located next to the markers Xgwm497(1A),Xwmc149(2A), Xwmc795(5A), Xgwm540(5B), and Xwmc539(6B). Both some A-QTLs andAA-QTLs were located next to the markers Xgwm99(1A), Xgwm624(4D), Xwmc740(5B) and Xwmc759(5B). Among these QTLs, QPL.cgb-2D.2, QTGW.cgb-5B.1, QTGW.cgb-5B.4andQGY.cgb-5B.4had greater contribution rates of phenotypic variation explanation than others, rangingfrom10.49%to13.88%. The contribution rates of phenotypic variation explanation of AA-QTLs next toXgwm400(7B) controlling the traits TSN and GNP were15.65%and19.89, respectively. These locicould be major QTLs for yield traits. And,epistatic effect was the major effect for genetic of wheat yieldassociated traits.4. Forty six A-QTLs controlling drought tolerance related physiological traits and88AA-QTLswere detected in all chromosomes except6A of the IL. In different environments and growing stages,the QTLs controlling target traits had different expression patterns. The AA-QTLs controlling2or moredrought tolerance related physiological traits were located next to the markers Xwmc149(2A), Barc159(2B), Xwmc795(5A), Barc141(5A), Xwmc759(5B), Xgwm138(5D), Xgwm560(7A) and Xwmc364(7B). And next to the markers Xwmc716(1A), Xwmc317(2B), Xwmc153(3A), Xgwm2(3A),Xgwm624(4D), Xcfd8(5D) and Barc204(6D), located both A-QTL controlling2or more droughttolerance related physiological traits and AA-QTL. Among these QTLs, QChlC.cgb-1A.3, QCT.cgb-1A.3,QCT.cgb-7A.1, QCTD.cgb-7A.1, QFLL.cgb-2B.1and QFLW.cgb-3A.1had greater contribution rates ofphenotypic variation explanation than others, ranging from10.02%to17.77%. These loci could bemajor QTLs for physiological traits of drought tolerance. The contribution rates of phenotypic variationexplanation of detected AA-QTLs ranged from12.93%to25.72%, indicating the great effect of epistaticeffect for genetic about these traits.5. The QTLs controlling important drought tolerance agronomic and physiological traits located indifferent chromosome or the different regions of one chromosome presented significant disequilibriumdistribution, and these QTLs assembled in some specific interval formed the hot-spot region. Total of17hot-spot regions consisted A-QTLs and53AA-QTLs were found. Among those, the hot-spot regionslocated closet to the region in1A between Xwmc24and Xgwm497,1B between Xgwm273andXwmc766,2A between Xwmc149,2B between Xwmc257and Xwmc317,2D between Xgwm261,3Bbetween Xwmc679,5A between Barc186and Xwmc795,5B between Xwmc740, Xgwm540andXwmc759, Xwmc539in6B, Barc204in6D and Xwmc364in7B, had become important hot-spotregions controlling significant wheat drought tolerance associated agronomicand physiological traits,which indicated these regions contained large amount of target gene.This study identified the genetic basis and expression pattern of drought tolerance associatedagronomic and physiological traits in wheat in a molecular level with IL, providing a theoreticalfundamental for the genetic improvement of drought tolerance in wheat. The detected stable expressedand multi-effect QTL also had important application in QTL-NIL building, QTL functional research andmap-based cloning. |
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