QTL Mapping Of Panicle Traits And Association Analysis Of Stigma Length In Rice

Rice is not only one of the three major grain crops in the world,but also one of the major staple foods of the Chinese people.With the acceleration of urbanization process and the reduction of arable land,it is the necessary to increase rice production by increasing the yield per unit area.Production practice has proved that,the yield of hybrid rice cultivar is higher between 15%-20%than that of conventional rice cultivar,therefore,the development of hybrid rice is necessary to meet the needs of people's food.Rice panicle is the ultimate embodiment parts of rice yield,the ideal panicle type can obtain higher yield of rice grain and also higher yield of hybrid seed production.It is of great significance to study the location and cloning of panicle related QTL in order to increase the yield of rice grain and F1 seed.Since rice is a self pollinated crop,the floral structure is conducive to self and not conducive to outcrossing,resulting in low hybrid seed yield.This characteristic has become one of the limiting factors in hybrid rice seed production.Therefore,improvement of rice floral traits for increasing outcrossing rate also has an important practical significance for increasing the hybrid seed production of rice.In this study,we conducted the following two studies.Firstly,QTLs for seven panicle traits were detected by using the genotyping data of the SSR markers and the phenotypic data collected in the population of chromosome segment substitution lines(IIA-CSSLs)constructed by an indica variety II-32B as receptor parent and a japonica variety A7444 as donor parent.Secondly,association analysis between SSR markers and stigma length was conducted by using the natural population composed of 254 rice varieties from different ecological regions and 262 pairs of SSR markers distributed on the chromosome of rice.We surveyed the stigma length in 2015 and 2016.We used 262 SSR markers to analyze genetic diversity,population structure and level of linkage disequilibrium.The relationship between the stigma length and SSR markers was analyzed by using the mixed linear model(MLM)in TASSEL software.The main results obtained are as follows.1.In the population of ?A-CSSL,a total of 26 QTLs for the panicle length,primary branch number,secondary branch number,spikelets per panicle,grains per panicle,1000-grain weight and grain width were identified located on chromosomes 1,2,3,5,6,7,8,9 across two years.Of the 26 QTLs,13 QTLs were detected in both years.Segments simultaneously controlling SBN,SPP and GPP were found on chromosomes 2,6 and 8.According to bi-parent DNA sequence comparison,QTLs qSBN6 and qSBN8 were speculated to be different from Hdl and DTH8 because 16 and 1 base difference were found,respectively.QTL qSBN2 seems to be a novel locus that controlling secondary branch number.2.There were significant differences for stigma length in the natural population composed of 254 rice varieties.The mean values for stigma length in 2015 and 2016 were 1.72mm and 1.78mm,respectively,and ranged from 1.29mm to 2.60mm,1.32mm to 2.66mm,respectively.The coefficients of variation for 2015 and 2016 were 15.2%and 13.4%,respectively.The broad-sense heritability for the stigma length was above 90%in each year.Three thousand and two hundred three alleles were detected in the population,and the average number of alleles per SSR locus was 12.2.The average gene diversity was 0.7914 and the average PIC value was 0.7694.Eighteen SSR marker loci associated with stigma length significantly(P<0.05)were detected in two year.Five loci were detected in both years,and they were RM345,RM336,RM269,RM7557 and RM167 on chromosome 6,7,10,0 and 11,respectively.The additive effect ranged from 5.03%to 13.2%.Based on marker loci detected,21 elite alleles and the varieties carried these alleles were mined for stigma length improvement.RM167-125bp had the largest phenotypic effect,with an average of 1.15mm,and the typical carrier variety is Nongxiang 26.The phenotypic effect of RM269-190bp was the lowest,and the average value was 0.09mm,the typical carrier variety is Jiangpuheimidao.