| Drought has been just a major limiting factor in wheat (Triticum aestivum L.) productionin semi-arid and arid area in China. Flag leaf in wheat is one of important photosynthesisapparatuses at the last growth stage. Especially, under the drought condition, keeping higherphotosynthetic rate of flag leaves will contribute to wheat grain yield. Accordingly, it isgreatly significant in discover the genetic basis of flag leaf under drought condition.Fastdevelopment of the molecular biology and the molecular quantitative genetics has provided anavailable approach to study the genetic mechanism of drought tolerance and its geneticpatterns for complex quantitative traits in wheat. Therefore, it is of very importance inconstructing the genetic linkage map, mapping QTLs and dissecting genetic basis for flag-leafcomplex quantitative traits related drought tolerance of wheat. These results show criticalsignificance of theory and practice in wheat research for molecular genetic improvement ofdrought tolerance and high or stable yield in the future.A recombinant inbred lines (RILs) with120progeny lines, derived from a cross betweenLongjian19(drought tolerant) and Q9086(water sensitive) were selected in this study. UsingSSR markers constructed a genetic linkage map. Four important traits in wheat, flag leaflength (FLL), flag leaf width(FLW), relative water content(RWC) and rate of excised-leafwater loss(RWL), were measured in different growth stages under drought and well-wateredconditions. And, QTL (quantitative trait loci) mapping analysis was performed by amixed-model composite interval mapping. The detailed results were available as follows:1. Total of405pairs SSR markers were available with showing SSR polymorphismdifferences between two parents of RILs from2187pairs SSR (Xpsp, Xgdm, Xbarc283,Xwmc and Xgwm) originally selected. The polymorphism frequency was18.52%. Thepolymorphism frequency of SSR showed, in turn, Xpsp(4.4%)＜Xgdm(9.0%)＜Xbarc(18.0%)＜Xwmc(22.7%)＜Xgwm(23.6%). Though the χ~2test (p<0.05), of all201SSR, mainlydistributed on A genome, showed the significantly segregation distortion with37.53%ofsegregation percentage, and80%of segregated distortion SSR markers resulted from femaleparent Q9086. Total of413SSR markers from358pairs SSR markers were mapped on21chromosomes of wheat. The linkage genetic map was covered3209.6cM. The average lengthper every chromosome was152.8cM, and the interval distances between two SSR markerswere average7.8cM on the linkage map.2. Total of25additive QTLs (A-QTLs) and26pairs of epistatic QTLs (AA-QTLs) wereidentified for controlling FLL and FLW of wheat in two water regimes. Of two traits,25 A-QTLs controlling FLL were mapped on chromosomes1B,2D,3A,4A,5A,5D and7A.These A-QTLs could explain H~2(A) ranged from1.05%to7.19%, and discover the H~2(AE)ranged from2.26%to10.73%. Moreover,12pairs of AA-QTLs were identified for FLL andtheir H~2(AA) ranged from1.20%to6.77%. Of all AA-QTLs attended in theQTL×environment interaction (QEIs), their H~2(AAE) ranged from1.83%to18.67%. ForFLW,15A-QTLs were detected on chromosomes1B,1D,2A,2B,3A,3B,4D,5A,5B,5D,6A,7A and7B. The H~2(A) ranged from1.84%to5.74%. Besides, total of14pairs ofAA-QTLs were identified with showed QEIs for FLW, which their H~2(AA) and H~2(AAE)ranged from0.31%to6.75%and from2.17%to20.4%, respectively.3. Under two water condition, of all5A-QTLs and13pairs of AA-QTLs were detectedfor controlling RWC and RWL of wheat. Of two traits, only two A-QTLs controlling RWCwere mapped on chromosome5B, showed the H~2(A) and H~2(AE)with9.91%and6.64%and24.84%and10.23%, respectively. And,11pairs of AA-QTLs were identified for RWC andtheir H~2(AA) ranged from1.53%to7.84%. Of all AA-QTLs showed QEIs with H~2(AAE)ranged from3.18%to20.7%. Only three A-QTLs for RWL were mapped on chromosomes2A,4D and6B with H~2(A) both are8.60%. Especially, A-QTLs on2A and4D were detecedthe QEIs with H~2(AE) of9.27%and9.16%, respectively. Besides, just two pairs of AA-QTLswere identified on chromosomes6A and1B with H~2(AA) of34.57%and34.76%, respectively.And one pair of AA-QTLs on1B showed the QEIs with H~2(AAE) of65.57%.In this study, the genetic linkage map constructed by SSR markers was suited for QTLmapping for the target traits FLL, FLW, RWC and RWL. All of target traits were essentiallysubjected to complex quantitative genetic regulated by minor-effect polygenes which wereeasily affected by different environments. The genetic factors regulating these traits consistedof additive, epistatic, additive QEIs and epistatic QEIs effects. Furthermore, of all QTLs forall target traits showed disequilibrium distribution among different chromosomes and evendifferent intervals in the same chromosome. These QTLs assembled in some specific intervalformed the hot-spot region for regulating inheritances of corresponding traits. These resultswould enhanced theoretical basis for the molecular genetic improvement of drought tolerancein wheat. |
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