Genetic Mapping Of QTL For Heading Date In Rice

Heading date is an important agronomic trait in rice,and is jointly influenced by genes and the environment.Mining genes controlling heading date,dissecting the underlying molecular mechanism,and exploring the interaction between different genes is of great use to have a comprehensive understanding of heading date regulation,and is of great significance to rice breeding,especially the cultivation of varieties suitable for different regions and seasons.In this study,mapping quantitative trait loci（QTL）for heading date was conducted using populations of the F₄ and F₅ generation that were derived from a cross between indica Hua130B and japonica dominant genic sterility plant,with a combination of bulk segregant analysis（BSA）and linkage analysis.Main results are listed below:1.Heading date of nine F₄ populations showed vast variation and different distribution trends,of which all did not meet the segregating ratio of 3:1 or 1:2:1,indicating that at least two QTL for heading date were existed in each population.2.Plants with extremely early heading and late heading in each population were mixed into two bulks respectively,and 100 markers that are evenly covering the rice genome were used to analyze genomic background of the two bulks of each population.Result showed that each population contained some segregating regions.Then,three populations（MQ1,MQ6 and MQ8）with a larger population size and fewer segregating regions were selected,and the rice genome breeding chip GSR40K was used to analyze genomic background of the two bulks derived from the three populations.Result showed that each population contained some segregating regions,and genomic difference of the two bulks from the three populations were only distributed on chromosome 7.3.To identify novel QTL for heading date,the population MQ1 was selected,and 52polymorphic molecular markers that covering heterozygous regions detected from chip GSR40K were developed.Genetic linkage map was constructed by genotyping 95 plants of population MQ1.A QTL analysis showed that three QTL,q Hd6,q Hd7 and q Hd8,were identified,which explained 13.53%,64.74%and 34.32%of the phenotypic variation,respectively.The three QTL contained the cloned major genes Hd1,Ghd7,and Ghd8,respectively.To further validate the effect of each QTL,the population size of MQ1 was increased to 142 plants,and QTL analysis showed that only q Hd7 and q Hd8 were detected,explaining 71.29%and 24.78%of the phenotypic variation,respectively.4.To verify whether q Hd6 has an effect on heading date,three plants carrying homozygous genotype for Ghd7 and Ghd8 but heterozygous q Hd6 regions in the MQ001 population were selected to develop the F₅ generation populations（Q1,Q2 and Q3）.For each population,plants showing extremely early heading and late heading were mixed into two bulks,and genomic background of each bulk was analyzed using the chip GSR40K.However,no difference was observed between the two bulks of each population.Then,the population Q3 was selected for further study.A polymorphic molecular marker was developed for each segregating region detected from chip GSR40K,and single marker analysis was conducted.Result showed that q Hd6 had no effect on heading date,but a region on chromosome 1 had effect.The local linkage map on chromosome 1 was constructed and linkage analysis was performed.A QTL q Hd1 on chromosome 1 was identified,which could explain 8.87%of the phenotypic variation.