Breeding of an Indica-compatible Japonica Photoperiod-sensitive Genic Male Sterile Line in Rice and Its Heterosis

The incomplete fertility of japonica x indica rice hybrids has inhibited breeders' access to the substantial level of heterotic potential of these hybrids.As hybrid sterility is caused by an allelic interaction at a small number of loci,it is possible to overcome it by simple introgression at the major sterility loci.Here we report the use of marker-assisted backcrossing to transfer into the elite japonica variety.Zhendao 88 a photoperiod-and thermo-sensitive male sterility gene from Lunhui 422S(indica) and the yellow leaf gene from the line Yellow 249(indica).The microsatellite markers RM276,RM455,RM141 and RM185 were used to tag the fertility genes S5,S8,S7 and S9,respectively.Line 509S is a true-breeding photoperiod-and thermo-sensitive genic male sterile(PTGMS) line,which morphologically closely resembles the japonica-type.Genotypic analysis showed that the genome of 509S had about 92% japonica DNA.Nevertheless,hybrids between 509S and japonica varieties sufferred from a level of hybrid sterility,although the line is highly cross-compatible with indica types,with the resulting hybrids expressing a significant degree of heterosis.Besides,the results suggested that segment substitution on fertility loci based on known information and marker-assisted selection was an effective approach to utilizing the heterosis of rice inter-subspecies.