Screening Of Marker Genotypes Of Elite Combining Ability And Improvement Of Combining Ability For Yield Traits In Parents Of Hybrid Japonica Rice(Oryza Sativa L)in The Jiang Huai Area

Rice(Oryza sativa L.)is a staple food for more than half of the world population.The increasing demand for rice in the world caused by population increase can only be met by enhancing yield per unit land area under the environment that both arable land acrage and water resources are decreasing.The practice over the past four decades has proved that planting hybrid rice was a successful technology for ebhancing yield per unit land area in rice.Seventeen million hectares of hybrid rice are grown in China,occupying about 50%of total rice area planted annually.Hybrid indica rice has alredy accounted for 60%of total indica rice area.The total area of japonica rice grown annually in China is 8.4 million hectares,and only 5%is occupied by japonica hybrid rice.Japonica hybrids still have great potential of development.The major reason for limiting japonica hybrid development speed was that competitive heterosis of hybrid cultivar was not conspicuous,compared with conventional cultivar in japonica rice.The key of enhancing competitive heterosis of hybrid cultivar in japonica rice was to improve combining ability(CA)of yield related traits in restorer lines.In the present study,two aspects of researches are carried out on what has already been achieved.Firstly,90 F1 combinations were made using 9 cytoplasmic male sterile(CMS)lines with BT-type cytoplasm and 10 restorer lines according to North Carolina Genetic Mating Design II(NCII).Six yield related traits of the 90 F1 combinations were investigated,and general combining ability(GCA)effects and variance of special combining ability(VSCS)of the 6 traits of the 19 parents were analyzed.Simple sequence repeat(SSR)marker genotypes for elite combining ability(CA)of the six traits,i.e.,yield per plant(YPP),panicles per plant(PP),total spikelets per panicle(TSP),filled spikelets per panicle(FSP),spikelet fertility(SF)and 1000-grain weight(TGW),were screened by combining the SSR maeker genotype data with CA data of the 19 parents.Secondly,improvements of CA for average grain yield per plant and productive panicles per plant in Ninghui 8,a restorer line of hybrid cultivar 86 You 8 that was cultivated in large scale in Jiangsu province,were carried out by using hybridization,backcrossing and assisted selection of SSR markers identified in this study.The main results obtained were the follows:1.Combining ability for the 6 traits in the 19 parents was analysed using the phenotypic data of 90 F1 combinations evaluated in Nanjing and Xuyi,Jiangsu province,and the results showed that BT-Wuqiang A was the best CMS line,and C 418 was the best restorer line across the two environments.2.Polymorphic products among the 19 parents were amplified in 78 of the 115 SSR primers using total DNA.SSR loci associated significantly with CA of the 6 traits in parents were detected using the SSR genotyping data of the 78 loci and phenotypic data of plants in 90 F1 conbinations.In Nanjing environment,8,12,11,6,6 and 3 of SSR association loci were detected with the CA of the six traits,namely,PP5 TSP,FSP5 SF,TGW and YPP,respectively,and the conresponding association loci were 12,20,8,15,10 and 8 in Xuyi environment.The numbers of association loci detected in both environments were 4,10,5,3,5 and 2,respectively.Out of the twenty-nine association marker loci detected in both environments,twenty three were associated with CA of only one trait,three for CA of two traits,and three for CA of three traits.RM406 on chromosome 2 associated simultaneously with CA of SF,TGW and YPP.Heterozygou marker genotype RM406-145/160 showed positive,negative and positive effects of CA in the three traits,respectively.RM16 on chromosome 3 associated simultaneously with CA of PP,TSP and TGW.Heterozygou marker genotype RM16-180/190 showed negative,positive and negative effects of CA in the three traits,respectively.RM340 on chromosome 6 associated simultaneously with CA of PP,TSP and FSP.Heterozygou marker genotype RM340-110/160 showed negative,positive and positive effects of CA in the three traits,respectively.RM208 on chromosome 2 associated simultaneously with CA of TSP and FSP.RM208-180/185 showed negative effects of CA in both traits.RM570 on chromosome 3 associated simultaneously with CA of TSP and YPP,and showed positive effects on CA in both traits.RM8263 on chromosome 7 associated simultaneously with CA of TSP and FSP.RM208-190/195 showed positive effects of CA in both traits.In Nanjing environment,76%(35/46)of the heterozygous genetypes of marker loci showed positive heterosis,and 55%(40/73)of the heterozygous genetypes of marker loci showed positive heterosis in Xuyi environment.3.By hybridizing,bachcrossing,selfing and testcrossing,7 new restorers with 280bp homozygous at marker locus RM570 in background of Ninghui 8 were obtained.The yield per plant of hybrids in 863A/8001-13-16 and 863A/8001-23-22 increased by 24.9%and 16.0%respectively,compared with that of 863A/Ninghui 8,the check combination.By hybridizing,bachcrossing,selfing and testcrossing,4 new restorers with 180bp homozygous at marker locus RM208 in background of Ninghui 8 were bred.CA for productive panicle per plant in 8010-4-10,8010-4-14 and 8012-2-9 enhanced by 23.1%,16.7%? 38.5%,respectively,compared with that of Ninghui 8,when crossed with CMS line 863 A.The improvements of CA above were involved only one locus for one trait.In the present study,six marker loci were detected associating simultaneously with CA of two or more traits.Those loci associated with CA of multi-traits consistent with breeding objectives might facilitate CA improvement for multi-traits simultaneously.Marker genotypes that were repeatly detected across locations and were associated significantly with CA of the same trait showed the same effect to F1 trait value in direction,and the percentage of increment was almost the same in different locations.Science the generality of improvement effects across locations,expectant results may be obtained by using the stable marker genotypes across locations for improving CA of restorer lines in japonica rice.863A/8001-13-16 and 863A/8010-4-10 had higher average grain yield and more productive panicles per plant than their corresponding check hybrid cultivars,whereas no significant difference between the combinations and their checks in plant height and growth duration.These two combinations,therefore,are hopeful to be used in production.