INTERGENERIC POLLEN-STIGMA INCOMPATIBILITY IN THE CRUCIFERAE

Abstract

Pollen tube inhibition on stigmas of open flowers was analyzed following 18 inter-generic pollinations among 10 self-incompatible taxa of Brassica, Raphanus, Eruca, Rapistrum, Diplotaxis, Iberis and Arabis. One cross was compatible, two were half compatible and the remainder were incompatible or slightly compatible. Fourteen of the pollinations also were made on stigmas of young buds and these, with one possible exception, were compatible. Three self-compatible species of Lepidium, Draba and Erucastrum accepted the pollen of four self-incompatible species but their pollen was incompatible on the self-incompatible species. A mechanism is postulated by means of which a self-incompatible Crucifer can recognize and accept pollen of its own species (or genus) while rejecting pollen of foreign species. A stigma also rejects pollen with a mutually active S allele. A macromolecular code with two pairs of sites, each with complementary structure, explains this behavior. The absence of intergeneric incompatibility in buds and in the self-compatible species studied suggests that the recognition mechanism is not operating there.