OCCURRENCE AND PHYSIOLOGICAL BREAKDOWN OF SELF-INCOMPATIBILITY IN EASTER CACTUS

The existence of self-incompatibility (SI) was demonstrated in 'Britto n' and 'Rose' Easter cactus (Rhipsalidopsis). In a full diallel cross among five clones, 18 out of 20 outcrosses resulted in 68 % to 100 % f ruit set, whereas reciprocal crosses between two of the clones and all five self-pollinations failed to set fruit. Pollen tube growth was gr eatly inhibited in styles of selfed pistils, but there was no evidence of pollen tube inhibition in compatibly crossed pistils. Easter cactu s exhibited characteristics typically found in sporophytic SI systems (trinucleate pollen, papillate stigmas, and scant stigmatic exudate) t ogether with those associated with gametophytic SI systems (stylar inh ibition of pollen tube growth and absence of reciprocal differences in outcrosses). Additional experiments were performed to determine the e ffects of bud pollinations, growth regulators (BA, GA3, and NAAm), and high temperatures (0- to 48-h exposure at 40C) on the SI response. He at treatments were more effective than either bud pollinations or grow th regulators in overcoming SI, and yielded an average of 7.2 viable s eeds per treated flower when plants were incubated for 12 h at 40C and selfed immediately after incubation. Isozyme analysis of the S. paren t and putative S, progeny confirmed that selfing had occurred followin g heat treatments. Using S, progeny in breeding programs may extend th e flower color range and lead to a greater diversity in other plant ch aracteristics than presently exists in cultivated germplasm.