Epistasis And Pyramiding Effects Of QTLs Related To Stigma Exsertion Rate In Wild Rice Species

The utilization of heterosis of rice(Oryza sativa)plays an important role in increasing the yield of rice.However,the low stigma exsertion rate of the CMS lines directly leads to a low outcrossing seeding rate,which increases the hybrid seed production costs.Genetic improvement of the stigma exsertion rate of rice is one of the main ways to increase the outcrossing rate of rice and the yield of hybrid rice.The stigma exsertion rate of wild rice,as the ancestor species of cultivar,is generally very high.And it is an important resource for genetic improvement of stigma exsertion in rice.In the previous study,our laboratory identified multiple stigma exsertion rate QTLs from the libraries of single-segment substitution lines of O.barthii,O.meridionalis and O.glumaepatula as donors.In this study,based on the wild rice chromosome single-segment substitution lines(SSSLs)with high stigma exsertion rate QTLs,a series of two-segment and three-segment pyramiding lines were constructed by hybridization and molecular marker-assisted selection.In addition,epistasis and pyramiding effects were analyzed.The main results are as follows:1.Analysis of the QTLs epistasis and pyramiding effects in the homozygous twosegment pyramiding lines.7 homozygous two-segment pyramiding lines were constructed using BAR-SSSLs and MER-SSSLs carrying stigma exsertion rate QTLs,including 4 BARpyramiding lines and 3 MER-pyramiding lines.The stigma exsertion rate of the BARpyramiding lines ranged from 40.26% to 84.68%,and that of the MER-pyramiding lines ranged from 35.17% to 47.73%.The phenotypes of the pyramiding lines were relatively stable between seasons and were significantly higher than those of the recipient parent HJX74.Except for B9 / B15,the phenotypes of other polymer systems were higher than those of the two SSSLs parents.In the QTLs combination of O.barthii,the additive-additive epistasis ranged from-19.10% to 18.13%;in the QTLs combination of O.meridionalis,the additiveadditive epistasis ranged from-19.06% to-5.96%.In BAR-pyramiding lines,the pyramiding effect ranged from 14.88% to 62.18%.B6/B19(q SERb3-1/q SERb12-1)was the best pyramiding combination with an average pyramiding effect of 55.51%.In MER-pyramiding lines,the pyramiding effect ranged from 7.81% to 25.24%.M7/M14(q SERm6-1/q SERm10-1)was the best pyramiding combination with an average pyramiding effect of 20.63%.2.Analysis of the QTLs epistasis and pyramiding effects in the homozygous three-segment pyramiding system.8 homozygous three-segment pyramiding lines were constructed using GLU-SSSLs carrying stigma exsertion rate QTLs.The stigma exsertion rate of the GLU-pyramiding lines ranged from 27.63% to 79.33%.G2/G11/G14 has the highest stigma exsertion rate,with an average of 75.30%.The phenotypes of the pyramiding lines were significantly higher than those of HJX74 in each season,and more than half of them were higher than their three SSSLs parents.The additive-additive-additive epistasis were significant and ranged from-72.44% and-10.14%.According to the analysis,the epistasis interaction of q SERg1-2/q SERg3-1/q SERg5-1 in G2/G11/G14 was the best.In the homozygous three-segment pyramiding lines,the pyramiding effect ranged from 5.14% to51.97%.The analysis shows that G2/G11/G14(q SERg1-2/q SERg3-1/q SERg5-1)was the best pyramiding combination,with an average pyramiding effect of 50.37%.3.Analysis of the QTLs epistasis and pyramiding effects in the different genotypes of G2/G11/G14 pyramiding lines.Different genotype combinations of G2/G11/G14 pyramiding lines were constructed,using G2、G11 and G14 carrying stigma exsertion rate QTLs.The stigma exsertion rate of these pyramiding lines ranged from 32.26% to 83.07%.The homozygous three-segment pyramiding line has the highest stigma exsertion rate,with an average of 81.20%.The phenotypes of the pyramiding lines were significantly higher than those of HJX74.The phenotypes of two-segment pyramiding lines were higher than their respective one or two SSSLs parents.The phenotypes of all three-segment pyramiding lines were higher than their respective three parents SSSLs.The epistasis ranged from-27.99% to34.51%.The epistasis effect of three-QTLs was higher than that of two-QTLs.The epistasis interaction of Aa Bb CC was the best with an average of 30.78%,and the contribution rate of epistatic effect to phenotypic variation is 12.03%.In G2/G11/G14 different genotype pyramiding lines,the pyramiding effect ranged from 6.74% to 57.70%.The pyramiding effect between the three SSSLs was higher than that between the two SSSLs.In G2/G11/G14 different genotype pyramiding lines,the analysis shows that the homozygous three-segment pyramiding line(AABBCC)was the best pyramiding combination,with an average pyramiding effect of 54.84%.In the present study,the pyramiding of stigma exsertion rate QTLs of wild rice was achieved.The pyramiding effects are all positive,indicating that these QTLs have a certain cumulative effect,and that it is possible and useful to increase the rice stigma exsertion rate through pyramiding.The analysis of epistasis and pyramiding effects among QTLs can enrich the theoretical research on stigma exposure and pyramiding in rice.A batch of pyramiding lines with excellent effects were obtained,which can provide valuable materials for rice pyramiding breeding.On this basis,the future research could continue to pyramid the stigma exsertion rate QTLs and improve the stigma exsertion rate of rice to increase the outcrossing seeding rate of rice.This study is of great significance to the genetic improvement of stigma exsertion and pyramiding breeding in rice.