Post-pollination barriers to intergeneric hybridization between Easter cactus [Hatiora gaertneri (Regel) Barthlott, H. rosea (Lagerheim) Barthlott, and H. ×graeseri Barthlott ex D. Hunt] and holiday cactus [Schlumbergera truncata (Haworth) Moran and S. ×buckleyi (Buckley) Tjaden] were determined and procedures were devised for circumventing these barriers. Examination of Hatiora and Schlumbergera pistils at 72 hours after intergeneric crosses indicated no abnormalities in pollen germination or pollen tube growth in the upper style. Pollen tubes of Hatiora were arrested in the lower half of Schlumbergera styles and failed to enter the ovary. Schlumbergera pollen tubes exhibited normal growth in Hatiora styles but most tubes lost directionality, burst, or failed to penetrate the micropyles after reaching the ovary. Three growth regulators (BA, GA3 and NAAm) were applied individually to ovaries of `Crimson Giant' Easter cactus after intergeneric crosses. GA3 and NAAm increased fruit set compared to the control (lanolin alone) or BA but none of the fruit harvested 160 days after pollination contained mature embryos. Four progeny were obtained when a short-styled S. ×buckleyi clone was crossed as a female parent with H. ×graeseri. Isozyme patterns and morphological characteristics confirmed that the four progeny were intergeneric hybrids. This is the first report of successful intergeneric hybridization between Hatiora and Schlumbergera. Chemical names used: N-(phenylmethyl)-1H-purine-6-amine [benzyladenine (BA)]; gibberellic acid (GA3); α-naphthaleneacetamide (NAAm).
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