Ponnaiya, B W XKarunakaran, KKAU2020-05-222020-05-221964http://krishikosh.egranth.ac.in/handle/1/5810146288PGThe evolution in the concept of geographical rices in Oryza sativa L. The nature and extent of sterility in inter-varietal hybrids and the different explanations for the same, heterosis and its utilization of rice breeding, and pachytene analysis as amethod of karyotypic studies in the genus Oryza with special reference to the intervarietal karyotypic diversity in O.sativa have been briefly reviewed.enThesis