Pyramiding Of Indica-Japonica Compatibility Genes And Their Genetic Effect Studies In Rice

The strong heterosis hybrid of indica and japonica,two subspecies of Asian cultivated rice,is one of the important approaches to further improve rice yield.However,breeding of indica-japonica hybrid rice was severely restricted by reproductive isolation.The discovery of“wide compatibility genes”and“specific compatibility genes”make it possible to overcome indica-japonica hybrid sterility and improve the seed setting rate of indica-japonica hybrid rice.In this study,the pyramiding line PL-（S5-n+f5-n）from‘9311⁶/Dular’progeny,the backcross line BC₂F₂ intermediate material（carrying pf12-j）from‘9311³/Dular’progeny and the backcross line CSSL-（Sc-j）from‘9311/Nipponbare’progeny were used as the research materials.By means of hybridization and pyramiding breeding strategy,combining foreground and background selection,we are going to create the near isogenic lines and pyramid lines possessing the compatibility genes with recipient parent genetic background.Furthermore,the genetic effects of single and multiple compatibility genes were further evaluated,and the effects of different compatibility gene combinations on the fertility recovery of indica-japonica were clarified,which provided the some implication for molecular breeding of indica-japonica heterosis.The main research results are as follows:1.Nipponbare,a typical japonica variety,and Dular,a typical wide-compatibility rice variety,were used as the donors of compatibility genes,while 9311,an indica rice variety was used as the recurrent parent in this breeding program.Through backcross breeding strategy,molecular marker-assisted selection,and the utilization of genome-wide breeding chip technology（RICE6K,GSR40K）,two near isogenic lines NIL-（Sc-j）and NIL-（pf12-j）were developed.The background recovery rates of 9311were 97.73%and 95.40%,respectively.Two pyramiding lines of three compatilibility genes,PL-（S5-n+f5-n+Sc-j）and PL-（S5-n+f5-n+pf12-j）,were obtained.The background recovery rates were 97.27%and 97.10%,respectively.In particular,S5-n and f5-n were wide-compatibility genes,while Sc-j and pf12-j were specific compatibility genes.The size of the introgressed Sc-j fragment was 8.41 Mb,and the size of the introgressed pf12-j fragment was 2.86 Mb.2.The main agronomic traits of all the breeding lines were investigated.PL-（S5-n+f5-n）showed no significant differences in all agronomic traits.NIL-（Sc-j）,NIL-（pf12-j）,PL-（S5-n+f5-n+Sc-j）,and PL-（S5-n+f5-n+pf12-j）had no significant differences to 9311 in day to heading,spikelets per panicle),seed setting rate,and yield.PL-（S5-n+f5-n+Sc-j）and PL-（S5-n+f5-n+pf12-j）showed significant decrease at 0.01 and0.05 probability level,respectively,as compared with 9311.In addition,the plant height of PL-（S5-n+f5-n+Sc-j）was significantly lower than that of9311,and number of panicle per plant of PL-（S5-n+f5-n+pf12-j）was significantly lower than that of 9311.The average panicle length of NIL-（Sc-j）was significantly lower than that of 9311,while1000-grain weight and seed setting rate of NIL-（pf12-j）were significantly lower than those of 9311.3.PL-（S5-n+f5-n）,four bred lines,and 9311 were test-crossed with japonica tester Nipponbare,Balilla and Laoguangtou83,and indica tester Nanjing 11 and IR64,respectively for analyzing the fertility effects of single and multiple compatibility genes under indica-japonica hybrid background.The results showed that the single allele pf12-j improved pollen fertility by 25.8%-33.6%,embryo sac fertility by 17.4%-39.7%,and spikelet fertility by 15.7%-26.0%in indica-japonica cross F₁.With pyramiding of the three compatibility genes S5-n,f5-n and pf12-j in the indica-japonica crosses,pollen fertility was increased ranging from 51.4%to 61.2%,embryo sac fertility from 30.8%to40.6%,and spikelets fertility from 44.2%to 59.7%.As compared with 9311,the pollen fertility of indica-japonica cross with single Sc-j was reduced by 12.0%on average,while the spikelets fertility was increased by 6.6%on average.With pyramiding of the three affinity genes S5-n,f5-n and Sc-j in the indica-japonica crosses,pollen fertility was improved ranging from 36.4%to 57.1%,embryo sac fertility from 33.0%to 36.7%,and spikelets fertility from 33.6%to 49.3%.All testcross F₁ derived from indica testers showed normal fertility,indicating that the breeding lines showed compatibility to indica.