Towards Fine Mapping Of Major QTLs Controlling Tolerance Against Nitrogen Deficiency In Rice

Nitrogen significantly improves the rice grain yield by enhancing yield and yield component traits.Nitrogen deficit leads toward a reduction in plant growth which ultimately causes yield reduction.Root traits have been considered the most important components associated with crop yields under nitrogen deficiency.In this study,a set of 75 Chromosomal Segment Substitution Lines(CSSLs)derived from an Indica nitrogen deficiency tolerant variety XieqingzaoB(XQZB)and an Indica nitrogen deficiency susceptible variety Zhonghui9308(ZH9308)was used.A genetic linkage map was constructed by employing 87 SSR and 33 InDel markers to analyze quantitative trait loci(QTLs)at seedling stage in rice under normal nitrogen(NN),low nitrogen(LN)and relative ratio(LN/NN)levels.A sum of 9 QTLs was detected in 6 regions on 6 chromosomes,with each QTL explaining 10.58%-27.27%of phenotypic variation.One of these QTLs namely,qRDWN6XB was determined to be a major QTL for root dry weight and located near marker InD90 on chromosome 6.The target chromosomal segment substitution line CSSL45,which has a higher root dry weight(RDW)than indica cultivar Zhonghui9308 and carry qRDWN6XB,was selected for further study.A secondary BC5F2:3 population derived from a cross between CSSL45 and Zhonghui9308 was constructed.To fine-map qRDWN6XB,we used the homozygous recombinant plants and ultimately this locus was narrowed to a 52.3-kb between markers ND-4 and RM19771,which contains nine candidate genes in this region.One of these genes,LOC_Os06g15910 as a potassium transporter was considered a strong candidate gene for the RD WN6XB locus.