QTL Mapping And Genetic Dissection Of Stigma Exsertion In CMS Line For Improvement Of Hybrid Rice Seed Production

The stigma exsertion rate is one of the most important traits which contribute to the efficient improvement of commercial seed production in hybrid rice.The efficiency of hybrid rice seed production can be improved by increasing the percentage of exserted stigmas.It is a polygenic inherited trait that is important for increased seed yield in hybrid rice breeding.In the first experiment,QTL mapping was conducted by using 134 recombinant inbred lines?RILs?derived from XieqingzaoB and Zhonghui9308,which has high and low stigma exertion rate,respectively.A total of eight QTLs?qSSE6,qSSE11,qDSE1a,qDSE1b,qDSE10,qDSE11,qTSE1 and qTSE11?for single stigma exsertion?SSE?,dual stigma exsertion?DSE?and total stigma exsertion?TSE?were detected.The qSSE11 and qTSE11 locations have not been previously reported,and qDSE11 allele inherited from the parent XQZB exhibited a positive additive effect.In addition,three QTLs qSNPP1,qSNPP3a and qSNPP3b for spikelet number per panicle?SNPP?were found.Especially,one QTL qSNPP1 was detected in two different environments?Hainan and Zhejiang?.In the second experiment,QTLs of stigma exsertion were detected by using 75chromosome segment substitution lines?CSSLs?developed from a cross between the donor parent,XieqingzaoB?XQZB?,a maintainer line which has high stigma exsertion and the recurrent parent,Zhonghui9308?ZH9308?,a restorer line which has low stigma exsertion.A total of nine QTLs?qSSE5,qSSE10,qSSE11,qDSE10,qDSE11,qTSE5,qTSE6,qTSE10 and qTSE11?for single stigma exsertion?SSE?,dual stigma exsertion?DSE?and total stigma exsertion?TSE?were assessed in two environments?Hainan and Zhejiang?.Six of these QTLs?qSSE10,qSSE11,q DSE10,qDSE11,qTSE10 and qTSE11?were found in both environments,while one QTL?qTSE6?was found in only Hainan,and two QTLs?qSSE5 and qTSE5?were found in only Zhejiang.The qSSE10,qSSE11,qDSE10,qDSE11,qTSE6,qTSE10 and qTSE11 alleles,which are derived from the parent XQZB,exhibited a positive additive effect.In contrast,the qSSE5 and qTSE5alleles,which are derived from the parent ZH9308,exhibited a negative additive effect.The SSE,DSE and TSE traits were significantly correlated with each other in an environmentally dependent manner.In the third experiment,the near isogenic line?NIL?was developed from same parental lines.Primarily identified a major QTL?qSE11?,located on chromosome 11 that was responsible for the high stigma exsertion rate.In the present study,used one of the CSSLs?C65?;the NIL(qSE₁₁^XB),which contained an introgression segment of XQZB in the genetic background of ZH9308,exhibited a significantly higher stigma exsertion rate than that of the parents.We demonstrated that qSE11 regulated both the single and dual stigma exsertion rates,which both contributed to the total stigma exsertion rate in rice.Genetic analysis revealed that qSE11 acted as a single Mendelian factor and that the allele from XQZB increased the stigma exsertion rate.The validity for stigma exsertion rate,C65 was used to build the secondary F₂?BC₅F₂?and F_2:3(BC₅F_2:3)populations by backcrossing to ZH9308 with subsequent selfing.We used 3600 individuals from the F₂population and 3200 individuals from the F_2:3 populations for genetic dissection program and dissected the major QTL qSE11 to a 350.7-kb region that located on rice chromosome 11.This study will be helpful for the future isolation of candidate genes of stigma exsertion.The genes controlling stigma exsertion rate will play a vital role in hybrid rice seed production programs.