Author : Kermicle, Jerry

Summary : Cross-pollinating plants regulate crossing so as to balance the depressing effects of inbreeding and the dysgenic effects of wide hybridization. Inbreeding is avoided by such means as separation of the sexes and differences in flowering time. Physiological self-incompatibility is especially important in some taxa. As a result of elegant genetic analysis, extensive physiological study, and the application of modern molecular biological techniques, a detailed understanding of self-incompatibility is emerging. At the other end of the crossing spectrum, indiscriminate hybridization is prevented by a combination of spatial, temporal and physiological factors. In contrast with self-incompatibility, the physiological basis of cross compatibility is poorly understood. Analysis in this case typically involves the genetic complexity of interspecific hybrids. This complication is alleviated to some extent in Zea mays, where various incompatibilities exist between and within subspecies.