Molecular Breeding Of The Indica Cytoplasmic Male Sterile Lines

Rice（Oryza sativa L.）is one of the most important food crops in the world.In the past half century,there have been two green revolutions in rice breeding technology.The first green revolution was the semi-dwarf breeding of rice in the 1960s.This revolution transformed high-stalk rice varieties into dwarf varieties.The second green revolution was the use of interspecific heterosis that occurred in the 1970s.Because of the recombination of the genes of their hybrid offspring,hybrid rice is prone to produce huge mutations and super-parent advantages,thereby greatly increasing the yield of rice,which plays a very important role in feeding the growing world population.Cytoplasmic male sterility and restorability of rice is the core content of hybrid rice production and application,and it is also the basis for the utilization of heterosis.In terms of ways to achieve heterosis utilization,there are mainly two ways:"crossing indica sterility lines and japonica restorer lines"and"crossing japonica sterility lines and indica restorer lines."The combination method of"crossing indica sterility lines and japonica restorer lines"can effectively increase the yield of rice seeds,reduce the cost of the seed production process,shorten the growth cycle,and expand the planting range of rice.Therefore,it is of strategic significance to carry out researches on the sterile line and maintainer line of the excellent rice cytoplasmic male sterility indica type gene for enriching rice genetic background,using heterosis,cultivating new rice varieties and human social development.This study pioneered the use of a single-gene restorer line（SGRL）with a genetic background of indica rice of Huajingxian74（HJX74）and carrying only one non-functional restorer gene from a different source as a maintainer line,and cultivated a batch of outstandingly sterile lines and maintainer lines to further complement and improve the rice"Three lines"molecular design breeding platform.Several results obtained by this study are as follows:1)Cultivation of HL-CMS indica sterile lines.Using rf5-SGRL with the genetic background of HJX74 indica rice and non-functional Rf5 genes derived from W22,W23and W24,respectively,as the maintainer line,it crossed with the HL-CMS type sterile line Gaohong A and backcrossed continuously to achieve nuclear replacement.Under the genetic background of HJX74,four indica-type sterile lines carrying HL-CMS type cytoplasm were bred.After 5 seasons of continuous observation and inspection,all showed a completely aborted phenotype.2)Cultivation of HL-CMS indica wide compatibility maintainer lines.Using the rf5-SGRL that non-functional restorer gene Rf5 from W22,W23,W24 and W27 to hybridize with the polymer material of the specific affinity and wide-affinity gene S5n/Scn,rf5/S5n/Scn can be aggregated together to breed 8 HL-CMS indica wide-affinity maintenance aggregates with affinity for japonica rice restorer lines.Cultivation of HL-CMS indica type high stigma exposure rate maintaining line.Using the obtained high-stigma-exposure QTL aggregation lines and SGRLs from W22,W23,W24 and W27,9 stigma-type maintainer lines with high stigma-exposure rates were bred by MAS.The stigma exposure rate of this type of maintainer lines are between 45-67%,which is 25-47%higher than the control HJX74.3)Cultivation of HL-CMS indica-type high stigma exposed rate maintainer lines.Using the QTL polyline with high stigma exposure rate that has been constructed by the predecessors and the rf5-SGRL from W22,W23,W24 and W27,9 indica-type maintainer lines with high stigma exposure rate were cultivated by molecular marker assisted selection（MAS）technology.The investigation of agronomic traits showed that the stigma exposure rate of this type of maintainer was significantly improved,which was 25-47%higher than that of the control HJX74.4)Cultivation of HL-CMS indica CMS lines with high stigma exposure rate.By using the HL-CMS indica-type maintainer line bred in 3)as reincarnation parents to backcrossed with the HL-CMS indica CMS line bred in 1),6 HL-CMS indica-type CMS lines with high stigma exposure rate was bred.The agronomic traits showed that the sterile lines of this type showed a completely aborted phenotype and the stigma exposure rate was25-49%higher than that of the indica-type HL-CMS lines.5)Cultivation of DA-CMS new gene source maintenance lines and its sterile lines.Using the non-functional restoring gene Rf3 in rf3-SGRL derived from W02,W07,W10and W11 and the non-functional restoring gene Rf4 in rf4-SGRL derived from W02 and W22 as the maintainer lines to backcrossed with the DA-CMS lines cultivated in our laboratory Huaxie A（HXA）,13 new CMS lines carrying DA-CMS sterile cytoplasm with completely aborted phenotype and lower neck wrapping rate were bred..6)Test cross between the new gene source maintainer lines and Gaozhou wild rice cytoplasmic sterility line.Using the new gene source maintainer lines cultivated in 5)above to test the sterile line G Ruanhua A carrying the cytoplasm of Gaozhou common wild rice,four F₁plant materials with cytoplasm derived from Gaozhou common wild rice were obtained.The results of the inspection all showed a completely aborted phenotype,and it was possible to continue backcrossing in the follow-up to cultivate a new gene source steriles line carrying the cytoplasm of Gaozhou common wild rice.In this study,by using rf3-SGRL,rf4-SGRL and rf5-SGRL,27 sterile lines and 17maintainer lines with HJX74 backgrounds were cultivated,and the laboratory’s"Three-line"molecular design breeding platform was improved and developed.This study cultivates rice that meet the requirements of production and application,and provides an example for the molecular design breeding of hybrid rice"Three lines"from theory to practice.