Sterility in the rice hybrids and its significance

The degree of sterility resulting in F₁ hybrids has been used by several workers while considering the relative affinity between the different varieties and sub-species within a species and that between different species. The authors contend that sterility cannot be used as a criterion and present spikelet sterility data in F₁ hybrids of inter-varietal, inter-subspecific and interspecific crosses in the cultivated rices to support this contention. They conclude that the evolution of the three sub-species (viz., japonica, javanica and indica) may have taken place independent of each other from the various ecotypes of the putative species Oryza perennis through introgression although the possibility of the indica giving rise to japonica on the one hand and the javanica on the other cannot be altogether ruled out.The consequences of such a mode of evolution are discussed and the possibility of the existence of a slightly different set of linkage groups in indica rices compared with that of japonica rices is suggested.