Unidirectional cross-incompatibility was detected when a segment of chromosome 6 was introduced from a common wild rice (W593A) into a Japonica type (T65wx). Besides the dominant gene Cinf(t), cinm, a recessive gene controlling incompatibility in the male parent, and SuCinf(t), a dominant gene suppressing the expression of Cinf(t), were involved in unidirectional cross-incompatibility. This unidirectional cross-incompatibility is due to the interaction between cinm, carried by 'T65wx', and Cinf(t), carried by 'W593A'. Furthermore, SuCinf(t) from the variety, 'Patpaku', is also involved in this interaction. These three genes form a gene complex, whose expressions occur before meiosis.