Improving The Ability Of C418 To Restore The Fertility Of The Japonica Cytoplasmic Male Sterility Lines Via Molecular Marker-assisted Selection

The seed setting rates of three-line japonica hybrids are lower than those of japonica inbred varieties,which restricts the hybrid vigor of hybrids on yield.Rfl8,a new restorer gene from 02428,a wide compatibility variety,has partial ability to restore the fertility of BT-type cytoplasmic male sterility(CMS)lines,have been mapped in our previous work.R1093,a chromosome segment substitution line derived from the cross between the donor parent 9311 and the recipient parent Nipponbare,has been identified to carry Rf6,a restorer gene for HL-type CMS,and can restore the fertility of BT-,HL-type japonica CMS lines.In the present study,Rf18 and Rf6 were pyramided into C418,a BT-type japonica restorer,using backcross via molecular marker-assisted selection,respectively,and the improved lines,C418Rf18/C418Rf6 were used to analyze the possibility that the ability of BT-type restorers to restore the fertility for BT-,HL-type CMS would be increased by pyramiding more Rf genes.The main results are as follows.First,STS 10-16 and STSH-7,the two makers linked to Rfl,were used to genotype 94 plants in BT-52605A/C418 F2 population.All the plants carried only homologous C418 or heterozygous genotype at these locus,and the ratio between plants with different genotypes was fit to 1:1(?2=0.681<?20.05=3.84).These results indicated there was only Rf1 locus in C418 for the fertility restoration of BT-type CMS.Second,two markers,RM407 linked to Rf6 and RM12941 linked to Rf18,were developed and exhibited polymorphism between R1093 and C418,02428 and C418,respectively.These two markers were used to genotype the plants in the backcrossing populations,and the numbers of plants with the target genes were close to the theoretical prediction,indicating that the two markers used in this study were effective for selecting the target genes.Third,BT-,HL-WA-type LiuqianxinA plants were crossed with C418,C418Rf18 and C418Rf6 plants,respectively,and the fertility of these testcrossed F1 plants were observed in two years.Compared with the testcrossed Fi plants from C418 and HL-,WA-type LiuqianxinA,the testcrossed Fi plants from C418Rf6 and C41SRf18 exhibited the increased fertility levels of 20%and 10%,respectively,and C41SRf6 lines can restore the fertility of HL-LiuqianxinA normally.Though C418Rf6 lines showed some improved effect on the fertility restoration of BT-type CMS lines,there were no significant improvement conducted by C418Rf6 and C418Rf18 lines.Fourth,six C418Rf18 lines and six C418Rf6 lines(G1-G12)were selected from BC3F4 and BC4F3 populations,and 14 agronomic traits of these improved lines were collected.The data from field trials demonstrated that most of the agronomic traits including yield were well maintained in the improved line compared to the parental control.Of these 12 improved lines,Gl,G9 and G10 exhibited the similar heading date and agronomic traits with the parental control.Last,the improved lines G1-G12 and C418 were used as male to cross with BT-,HL-LingfengA,resulting in 25 Fi hybrids,of which the agronomic traits and yield traits were observed.Compared with BT(HL)-LingfengA/C418 Fi hybrids,the yield per plant and seed setting rates of the BT(HL)-LingfengA/C418Rf6 Fi hybrids not the BT(HL)-LingfengA/C418Rf18 Fi hybrids increased significantly.These results indicate that the effect of Rf6 for increasing the ability of BT-type restorers is better than that of Rfl8,and the application of Rf6 in improving the recovering ability of BT-type japonica restorer lines has good prospects in future..