Abstract

                                Cytogenetics of rice and rice hybrids has not been fully studied inspite of its economic importance. One field of study is hybrid sterility. It is well established that hybrids between indica and japonica sub-species of rice show varying degrees of sterility and also that by normal selection fertile types can be secured in the progeny. The occurrence of semi-sterility in hybrids between plants of the same species namely O. sativa L. is of theoretical interest and hence a detailed study of the nature of this sterility has been undertaken at the Central Rice Research Institute. During such a study it was found that the hybrids between indica and japonica varieties are a good source of chromosome variability and an instance of such a variant-secured from hybrid progenies is given below. The mode of origin of such variants is inferred to be caused by the cryptic chromosomal structural differences present in the sub-species affecting the meiotic mechanism thus resulting in chromosome variability in later generations. A study of such chromosome variations would be of use in interpreting differences between the indica and japonica sub-species and also in tracing the evolution of cultivated rice. The variants may also have use in rice breeding, for it is well known that aneuploids have been successfully used in other crop plants like wheat (Sears 1953 and Sikka et al., 1956) and tobacco (Cluusen and Cameron 1944).

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