New Methods Developed And QTL Mapping For Flowering Time In Rice

Rice is a typical self-pollinated crop,so the trait of flowering time has no effect on productivity,whether early or late.However,as the large-scale popularization and application of hybrid rice in the1970s,flowering time?FT?asynchrony between male and female parents become gradually one of the main factors limiting production of hybrid seeds,especially to those potential heterosis combinations between Japonica and Indica in the 21st century,due to the japonica CMS's difficulty of stigma exsertion during flowering.The genetic mechanism research of flowering time has been gradually given attention by breeders,which may give a new insight into that issue.In the present study,an early flowering time?EFT?mutant and normal rice were used for constructing populations for new methods exploring of studying flowering time trait,genetic analysis,genetic linkage map construction and QTL mapping.The main results are summarized as following:1.Environmental influence on flowering time:EFT and NIP were sowed by stages and their flowering time under the different environment were Investigated.Results indicated that flowering time delay under a lower temperature or shorter day length,which were in accord with previous studies2.Improved methods for studying flowering time:New methods for studying flowering time trait were explored to mitigate impact from natural and human factors.The new investigation method according to actual flowering time interval between EFT parent and RIL population has advantages of shorter investigation cycle and higher precision.It will provide important reference for further study on flowering time.3.Genetic analysis:F₁,F₂ and BC₁F₁ populations were constructed by the crosses between EFT and typical japonica Nipponbare?NIP?,typical indica TN1,9311,Zhongzu14.All F₁ plants showed the early flower phenotype and the segregation ratio of early flowering time plants to normal plants in F₂populations fitted to 3:1.In addition,the segregation ratio of BC₁F₁ populations was 1:1.The results indicated that the trait of early flowering time is controlled by a single dominant gene,including minor genes regulation and environmental effect.4.Genetic linkage map construction:The genetic linkage map containing 193 SSR and InDel makers was constructed based on RIL stable population with 184 individuals from the cross between EFT and NIP.The map covered a total length of 1753.3 centimorgan?cM?with an average distance of9.1 cM between adjacent makers.5.QTLs mapping for flowering time:A total of 7 QTLs for flowering time were located,which were distributed on the chromosome 1,5,9 and 12,explaining the phenotypic variation from 7.57%to66.8%.All the QTLs were novel except qFT-1c.Significantly,qFT-1a was regarded as a major QTL,accounting for 66.8%of phenotypic variation with LOD value 6.94,and its additive effect derived from early flowering time parent EFT.Further researches need conducting to verify the prediction.6.QTLs mapping for related traits:Correlation analysis of related traits with flowering time reveled that flowering time trait had no correlation with grain length,grain width or ratio of grain length to width,but whether there was a correlation between flowering time trait and heading date was undefined.QTL analysis showed that QTLs for flowering time had no overlap with the four traits.A total of 6 QTLs were detected for heading date,distributing on the chromosome 3,8,9 and 11.And 10QTLs were located for traits related to grain shape,which were distributed on the chromosome 2,7,8,9,10,11 and 12.Of all the QTLs,the heading date QTL qHD-11a,grain length QTL qGL-12,grain width QTL qGW-8,qGW-9 and the ratio of grain length to width QTL qRLW-7,qRLW-9,qRLW-10,qRLW-11were novel QTLs.