Improvement Of Yield Traits And Mapping QTL Using Low Phosphorus Tolerance Selected Introgression Lines Of Rice(Oryza Sativa L.)

The low utilization rate of phosphorus is a major limiting factor in riceproduction. In order to explore the favorable genes of rice tolerance to lowphosphorus, phosphorus foster efficient varieties, in our study, four BC2F4backcrossing populations were developed from the elite indica restorer linesShuhui527and Minghui86as the recurrent parents, Yetuozai and Pokhreli as donorparents. Yield and its related traits of the backcrossing populations were evaluatedand analyzed under normal control and phosphorus deficiency conditions. SSRpolymorphic molecular markers were used for genotypic analysis. One-way analysisof variances (ANOVA) and chi-square test were applied to identify QTLs for all themeasured traits.1. The results of the study suggested that the variation of thousand grain weight(TGW) and panicle length (PL) is small. There was a greater variation of traits whichwere constrained by the environment factor, such as panicle number (PN), flled-grainnumber per panicle (FGP) and spikelet fertility (SF). Low phosphorus stress have agreater impact on PN, FGP and YD, of which, PN was reduced a maximum degree bylow phosphorus stress, leading to a lower yield.2. The results of correlation analysis showed that YD and PN, FGP, spikelets perpanicle (TNSP) were in a highly significant or significant positive correlation undernormal and low phosphorus stress conditions. The correlation between PN and FGP ismanifested as a significant or very significant negative level. Thus, we should notonly pay attention to the improving amount of tillers, but also take filled-grain numberinto account in the practice breeding.3. The results of path analysis showed that, PN provided the largest direct effectfor YD under normal conditions in four populations. This result is consistent with thecorrelation coefficient analysis results. FGP provided the largest direct effect for YDin the two populations of Minghui86background under the low phosphorusconditions, indicating that FGP should be considered in this genetic background underthe low phosphorus conditions.4. The results of identified QTLs conferring YD and its related traits revealedthat23,19，25,20,25，19,21and21QTLs controlling PH, PN, PL, FGP, TNSP, SF,TGW and YD were detected respectively under two conditions. Under two treatments,the Shuhui527/Yetuozai, Minghui86/Yetuozai and Shuhui527/Pokhreli were detected respectively5,2and6main effect stable expression locus.5. The results of QTL detection showed that two QTL were identified in theShuhui527background, of which, qSF9(near RM257) which control SF wereidentified in two environments with negative additive effects, indicating that the allelefrom Shuhui527can improve SF. In Minghui86genetic background,4QTLcontrolling the same trait were identified.Of which, qFGP10and qSF10(near RM147)control FGP and SF, and they had high explained phenotypic variation percentage,indicating that the presence ofl the important locus controlling phosphorus effect. Theresults of QTL detection showed that5QTL controlling the same trait were identified.Of which, qTGW4(near RM335) which control TGW were identified in the Shuhui527/Yetuozai in two environments with high explained phenotypic variationpercentage, indicating that the presence of the main-effect locus controllingphosphorus effect. qSF11, which was tightly linked with RM287, control the sametrait of SF. It was also detected under normal and stress environments in Shuhui527/Yetuozai population, indicating that qSF11might be a stable expressed locus.6. Thirty and twenty-four pleiotropic QTLs were identified under normal andlow phosphorus conditions. The loci (near RM498) controlling SF, TGW and YD inShuhui527/Pokhreli, indicating that the allele from Shuhui527can improve thesetraits, it could be applied in the MAS for the simultaneously improvement of thesetraits. Some pleiotropic QTL were unfavorable for the simultaneously improvement ofdifferent traits. For example, the loci (near RM169) controlling PH, PN, PL, TNSP,SF and YD, the favorable alleles from donors can improve PN and SF while thefavorable alleles from Shuhui527can improve PH, PL, FGP and YD. It suggested thatthe introgressed alleles of donor in this locus can increase PN and SF while decreaseTNSP.