Detection And Validation Of 11 Minor QTL For Heading Date In Rice

Heading date?HD?plays a key role in regional and seasonal adaptation of rice cultivars.Proper HD is essential in maintaining an appropriate balance between full use of resources and avoidance of environmental stress in rice.In this study,we used five rice populations to detect and validate quantitative trait loci?QTL?for HD,aiming at discovering new QTL to be as candidates for gene cloning and marker-assisted breeding.Rice materials contained a recombinant inbred line?RIL?population derived from crosses between indica rice cultivar Teqing and near isogenic lines of IR24,and four secondary populations derived from the progenies of the original population.First of all,lingkage map of RIL population constructed previously and its HD data recorded for three years were used to perform QTL analysis.Then,we selected two residual heterozygotes from Teqing/IRBB52 F₇population through marker assay,selfing to produce two S₁ populations,Ti52-2 and Ti52-3.Three of four QTL detected in the RIL population fell into one segregating region of one population at least,and another fell into the homozygous region of two populaions.For further validation and detection of QTL,S_1:2 and S_1:3 families of them were developed and grown in Hangzhou and Lingshui,respectively.Choosing three QTL from those detected as targets,we selected two residual heterozygotes from Ti52-2S_1:2 lines,only heterozygous in one or two target regions and homozygous in all other QTL regions.The detail results were summarized as follows:HD data from RIL population for three years were analyzed jointly by QTLNetwork 2.0 and four QTL were found distributed on chromosome 3,5,10 and 12,additive effects and contribution of which were 0.39-0.82 d and 1.9-7.9%,respectively,as well as total phenotypic variance explained by these QTL were 17.5%;all four QTL were significant and have stable effects in the three years.QTL analysis for the S_1:2 and S_1:3 families of Ti52-2 and Ti52-3 populations was performed using Windows QTL Cartographer 2.5,respectively.A total of ten QTL were mapped on 8 chromosomes,whose additive effects and contribution were 0.21-1.63 d and 2.3-24.2%,respectively,and total phenotypic variance explained by these QTL were 26.9-60.2%in one population at one location,much larger than the original population,what's more,the original QTL were also well validated in the secondary populations.It's shown that using secondary population with more homogenous genetic background can not only validate QTL in the primary population,but can detect new QTL,increaing the efficiency of mapping minor-effect QTL.Similarly,we utilized ZC9 and ZC12 populations to analyze the effects of the three target QTL,which indicated that their effects had the same directions as the original QTL regions and also had the stable magnitude across diffirent populations and/or diffirent locations.Altogether,three of four QTL detected using the RIL population were validated in the secondary populations.Moreover,7 new QTL were mapped in the secondary populations.Thus,this study detected 11 QTL totally,and all of them were apt to have not strong photoperiod sensitivity.They could be used for fine-tuning rice heading date to optimize the utilization of environmental resources.Of these QTL,four corresponding to the genes/QTL that have been cloned or fine-mapped had much less effects,which is in support of the assumption that qualitative and quantitative genes are different alleles at the same locus,suggesting that it may be promising to identify minor-QTL from major heading date genes/QTL that have been cloned.The remaining seven QTL,inconsistent with those having been cloned or mapped,could be as candidates for gene cloning and marker-assisted breeding.