Studies on the cytoplasmic difference among rice varieties. Oryza sativa L. : I. On the fertility of hybrids obtained reciprocally between cultivated and wild varieties.

1) Hybrids among cultivated rice varieties are sometimes fertile and sometimes sterile according to the degree of afiinity between parental varieties. There is, however, no difference in the hybrid fertility between the reciprocal drosses, regardless whether the hybrid is fertile or poorly fertile. Such is the case with the crosses between an Indian variety, Surjamkhi, and two Japanese varieties, Sensho and Tsurumochi No. 1, as shown in Figures I and 2. 2) The situation with the crosses between cultivated and wild varieties is quite different. Seven cultivated varieties, including five Japanese and two Indian, were crossed reciprocally with two wild ones in ten combinations, the latter consisting of one Indian, O. sativa L. var. fatua L. and one Chinese variety, f. spontanea. All these crosses showed a remarkable difference in fertility between the hybrids from reciprocal matings. llybrids originated from the cross in which a wild variety partook as [the female parent showed, always a lower degree in both the seed-setting and pollen fertility than those from the reciprocal cross did (Figures 3 and 4).