UNILATERAL INCOMPATIBILITY WITHIN THE BRASSICACEAE - FURTHER EVIDENCEFOR THE INVOLVEMENT OF THE SELF-INCOMPATIBILITY (S)-LOCUS

Unilateral pollen-pistil incompatibility within the Brassicaceae has b een re-examined in a series of interspecific and intergeneric crosses using 13 self-compatible (SC, Sc) species and 12 self-incompatible (SI ) species from ten tribes. SC x SC crosses were usually compatible, SI x SC crosses showed unilateral incompatibility, while SI x SI crosses were often incompatible or unilaterally incompatible. Unilateral inco mpatibility (UI) is shown to be overcome by bud pollination or treatin g stigmas with cycloheximide - features in common with self-incompatib ility. Treating stigmas with pronase prevents pollen tubes from penetr ating the stigma in normally compatible intra- and interspecific polli nations. The results presented show that the presence of an incompatib ility system is important in predicting the outcome of interspecific a nd intergeneric crosses and, combined with the physiological similarit ies between UI and SI, would suggest an involvement of the S-locus in UI.