QTL Mapping For Phosphorus Efficiency And Morphological Traits At Seedling And Adult Stages In Wheat

Wheat(Triticum aestivum L.)is one of the most important staple crops in the world,whose productivity and quality is very important for agricultural sustainable development and the food supply.Phosphorus(P)is one of the three most important nutrients for the growth and yield improvement of wheat.However,an insufficient supply of available P in the winter wheat-producing areas in China is one of the major limiting factors of production.A lot of P fertilizers(P2O5)are supplied every year to grain high wheat productivity.But P efficiency(PE)of wheat is only about 10 %,which increased crop production costs,exhausted nonrenewable P resources,and caused a series of environmental problems.Therefore,it is necessary to map QTLs for PE related traits and excavate important genes and QTLs so as to provide reference for molecular marker-assisted selection(MAS),pyramiding breeding and gene clone to improve PE of wheat itself.In this study,we mapped QTLs for the PE and morphological traits under the hydroponic culture and field trials using two recombinant inbred lines(RILs)derived from ?Tainong 18 × Linmai 6?(TL-RILs)and ?Shannong 0431 × Lumai 21?(SL-RILs)with normal and low P treatments(NP and LP)through different years respectively.The main results are as follows:(1)Analysis of variance showed LP could reduce the biomass traits(SDW and TDW)and P uptake efficiency(PupE)traits(SPC,RPC and TPC),but increase RSDW,RSPC and P utilization efficiency(PutE)at the seedling stage of both RIL lines.Similarly,LP reduced yield and PupE traits(PH,SN,TGW,GWP,StWP,GPC and StPC),but increased PutE traits(GPutE and StPutE)at maturity stage of TL-RILs.Significant difference between genotypes and treatments existed in all targeted traits(p ? 0.01).Additionally,the broad-sense heritability(hB2)of 24 investigated traits of TL-RILs varied from 51.12 to 92.61 %,and the hB2 of 11 seedling traits of SL-RILs different form 58.21 to 90.43 %.(2)Correlation analysis of both RILs at seedling stage showed that significant correlation relationship were between four biomass traits(SDW,RDW,TDW and RSDW)and seven PE traits(SPC,RPC,TPC,RSPC,SPutE,RPutE and TPut E),indicating the seedling biomass traits were able to primary selection indexes for PE traits.The correlation analysis of TL-RIL at maturity stage showed the r between five yield traits(SN,PH,TGW,GWP,StWP)and four PE traits(GPC,StPC,GPutE and StPutE)and between two relative traits(Rgwp and Rstwp)and the four PE traits were significant and positive,suggesting that these five yield traits and two relative traits can also be used as primary indexes to evaluate PE traits.Moreover,the 11 seedling traits were also significantly correlated to six yield traits(SN,PH,SL,TGW,GWP and StWP)and two PupE traits(GPC and StPC)at the maturity stage of TL-RIL,showing that some seedling traits could reflect maturity traits to a certain extent.(3)For 30 investigated traits of TL-RILs,a total of 178 additive QTLs were detected under the hydroponic culture and field trials,including 163 QTLs for seedling and maturity traits and 15 QTLs for relative traits,distributing on 21 chromosomes.An individual QTL could explain from 4.52 to 51.68 % of phenotypic variation.Among them,81 QTLs showed positive and additive effects with Tainong 18 increasing the QTL effects,but 97 QTLs showed negative and additive effects with Linmai 6 increasing the effects of QTL.The highest LOD of single QTL for RSDW was 36.00 in NPAV treatment,which explained 51.68 % of phenotypic variation.Forty-nine and 63 QTLs were identified in LP and NP treatment respectively.Only 11 relatively high frequency QTLs(RHF-QTLs)were detected in more than a half of all treatments.Especially,QRsdw-4B could be detected in all four different treatments and AV.Furthermore,we found ten QTL clusters(C1-C10)distributed on 1A,1D,4B,5D,6A,and 6B chromosomes,involving 80 individual QTL loci,accounting for 36.53 % of the total QTL loci for trait-treatment combinations.We classified the ten QTL clusters into two types: type I,including C1,C2,C7,C8,and C10 detected only on seedling traits,and type II,including C3-6,and C9 observed simultaneously on seedling and maturity traits.Of these,four QTL clusters(C3,C5,C7,and C9)contained seven RHF-QTLs,which controlled PutE and morphological traits at the same time and positive relationship were found between them.Moreover,the sequences of twenty-nine molecular markers associated with 51 QTLs in our study were highly homologous with ESTs probably,including 19 QTLs special to LP treatment,16 QTLs special to NP treatment,four RHF-QTLs and six QTL clusters.These QTLs and their neighboring region were likely to link with potential functional loci.(4)For 11 seedling traits of SL-RILs,a total of 86 additive QTLs were identified under the hydroponic culture trials distributing on 18 chromosomes except for 1D,2A,and 3D.Single QTL explained from 6.41 to 19.55 % of phenotypic variation.Of these,Shannong 0431 increased the additive effects of 26 QTLs,whereas Lumai 21 increased the additive effects of 60 QTLs.The highest LOD of an individual QTL for SPutE was 10.36 in NPAV treatment,which could explain 17.93 % of phenotypic variation.Twenty-seven and 30 QTLs were detected in LP and NP treatment respectively.Only three RHF-QTLs(QSdw-4D,QSpute-4D,and QTpute-4D)were identified.We found seven QTL clusters(C1-C7)distributed on 4D,5A,and 5B chromosomes,involving 46 individual QTL with proportion of 42.59 % in total QTL loci for trait-treatment combinations.Particularly,one cluster on 4D chromosome C1 contained five QTLs,including three RHF-QTLs.The additive effects of these QTLs(QTdw,QSdw,QSpute,and QTpute)were increased by Lumai 21(except for QRsdw),suggesting this QTL locus may improve PutE and biomass traits simultaneously.Furthermore,we found sixteen molecular markers associated with 31 QTLs were highly homologous with EST sequences possibly.Among them,eight and ten QTLs were identified specially under LP and NP treatment.Three RHF-QTLs and three QTL clusters(C1,C2,and C6)were closely linked to ESTs probably,indicating some potential functional loci may underline these QTLs.(5)Comparing the QTL mapping results of TL-RIL with that of SL-RIL,we found almost all QTLs were located in different confidence intervals.Only one QTL for GN of TLRIL and one QTL for RSPC of SL-RIL were co-located on 7B chromosome near the marker wPt-6156.The possible reason was the distinct genetic background and different component markers.In a word,some QTLs identified in our study will contribute to breeding by allowing more rapid examination and selection of PE and morphological traits of wheat.