Genetic Dissection Of Two QTL Controlling Grain Weight In Rice(Oryza Sativa L.)

The world food security is affected by ever-increasing population,urbanization,climate change and reduction of arable land The potential solution to meet the food demand is the improvement of crop yield.Rice is one of major cereal crop and considered as stable food for half of the world population.However,increasing rice grain yield one of principle focus of the researcher.Recent development in genomics has helped in the identification,fine mapping and functional analysis of genes controlling yield in rice,Therefore,rice cultivar/lines with high yield performance is essential to meet food demands.Rice grain yield have three components;a number of grains per panicle,tiller number and 1000-grain weight(TGW).Among these components,grain weight is an important one.To explore the genetic mechanism that controls grain weight,we mapped two novel quantitative trait loci(QTL)qTGW1.1 and qTGW1.2 in different genetic background.We utilized homozygous recombinants method to map the QTL.1.In the first experiment,qTGW1.1 was mapped in chromosomal substitute segment lines(CSSLs).Primarily,qTGW1.1 was validated between marker InDel15 and RM12276 in CSSLs line named 9X7 on long arm of chromosome one.A CSSLs 9X7 with an introgression segment from XieqingzaoB(XQZB)as a donor parent with a genetic background of Zhonghui9308(ZH9308).A near isogenic line(NIL)was developed from the same parental lines.In this experiment 9X7 and NIL {TGW1.1),which contain segment from donor parent XQZB,exhibit significantly higher grain longer and wider grain than recurrent parent ZH9308.9X7 was backcrossed with ZH9308 to produce secondary mapping population F2(BC5F2),F2:3(BC5F2:3),and F3:4(BC5F3:4).qTGW1.1 was validated and mapped in three secondary population.Homozygous recombinant plants were used to map qTGW1.1.The genomic region was narrow down to 96.38kb between D-12 and TG-23,that contains 18 candidate genes,of which LOC_Os01g61044 encodes transmembrane amino acid transporter and considered as a strong candidate gene for qTGW1.1.Altogether,these results reveal a foundation for the cloning of qTGW1.1 and molecular breeding in rice.2.In the second experiment,we mapped QTL named qTGW1.2 on shot arm of chromosome one using the introgression line.An introgression line(IL7422)was identified with the introgression segment from Oryza rufipogon Griff known as wild rice(CWR)in BC4F6 generation with a genetic background of Zhonghui8015(ZH8015).The IL has less wider grain and low TGW as compared to ZH8015.Firstly,qTGW1.2 was mapped in BC4F6 in Introgression line(IL7422).To further map and dissect this QTL(qTG W1.2),IL7422 was backcrossed with ZH8015 to produce two secondary mapping population F2(BC5F2),F2:3(BC5F2:3).Initially,qTGW1.2 validated between marker RM10018 and RM3747 in F2(BC5F2)mapping population.Genetic disection was done by using homozygous recombinants method(HZRM).In F2:3(BC5F2:3),homozygous recombinants were selected between RM10114 and TG-30.Finally,qTGW1.2 was delimited to a genetic region of 480.45 kb between GHB20 and AD-11 on the short arm from chromosome one.The alleles from CWR rice control the grain size and grain weight in NIL(TGW1.2).The target region contains 76 genes.However,genome-wide sequencing can be performed to find the candidate gene for qTGW1.2.Our results lay foundation for the cloning of qTGW1.2 and its further application in rice breeding program for genetic improvement.