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Renate Karle, Constance A. Parks, Maureen C. O'Leary, and Thomas H. Boyle

Spontaneous chromosome doubling occurred in shoot apices of two diploid (2n = 22) Hatiora ×graeseri Barthlott ex D. Hunt (Easter cactus) clones and yielded stable periclinal cytochimeras with a diploid epidermis and tetraploid subepidermis. The cytochimeras produced disomic gametes (n = 22) and displayed tetrasomic inheritance at polymorphic isozyme loci. Diploid clones were highly self-incompatible (SI) but both cytochimeras were self-compatible (SC). Analysis of pollen tube growth in selfed or outcrossed styles revealed that polyploidy altered the incompatibility phenotype of pollen without affecting the incompatibility phenotype of the pistil. Morphological data (guard cell length, stomatal density, and pollen diameter), segregation ratios at isozyme loci, and fruit/seed yields indicate that S1 progeny are SC, nonchimeral, and tetraploid. Breakdown of the SI system in the cytochimeras was attributed to formation of compatible heteroallelic pollen. These results provide a rational explanation for the correlation between ploidy level and breeding behavior in cacti. Production of SC autotetraploid clones from SI diploids by chromosome doubling may be useful in development of cacti as fruit crops.

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Renate Karle and Thomas H. Boyle

The effects of floral morphology and breeding behavior on flower longevity were investigated in Easter cactus [Hatiora ×graeseri (Werderm.) Barthlott)]. Four clones were studied: two diploid (n = 11) clones (`Evita' and `Purple Pride') that were highly self-incompatible (SI), and two cytochimeras (diploid epidermis and tetraploid subepidermis) that were recovered from the diploid cultivars, both of which were self-compatible (SC). The clones exhibited differences in the stage of floral development in which autogamy commenced. Autogamy commenced on the day of anthesis in the two `Evita' clones and occurred ≈5 days after anthesis in the `Purple Pride' cytochimera. In the `Purple Pride' diploid clone, anthers and stigmatic lobes remained spatially separated during the period from anthesis to senescence. Examination of styles collected from senesced, undisturbed flowers showed that few pollen tubes traversed to the base of the styles for the two SI diploid clones, whereas large numbers of pollen tubes were present at the base of the styles for the two SC cytochimeras. Flower longevity for the `Evita' cytochimera was significantly less than for `Evita' diploid, but the diploid and cytochimeral clones of `Purple Pride' exhibited similar flower longevities. Application of 2 mm silver thiosulfate, an inhibitor of ethylene (C2H4) action, did not affect flower longevity of `Evita' cytochimera. Our results show that flower longevity in Easter cactus is influenced by breeding behavior and the stage of floral development at which autogamy commences.

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Susan S. Han and Thomas H. Boyle

Experiments were performed to determine the effects of ethylene (C2H4) on the postproduction quality of Easter cactus [Hatiora gaertneri (Reg.) Barthlott and H. ×graeseri (Werderm.) Barthlott]. Significant differences in percent bud abscission were observed among cultivars when plants were exposed to 0.4 or 1.0 μL·L-1 C2H4 for 48 hours. Fewer buds abscised on `Andre' and `Red Pride' than on `Evita', `Rood', and `Thor-Anne'. Stage of floral development at the time of C2H4 exposure affected the pattern and severity of bud abscission for `Crimson Giant'. Percent bud abscission was greater for plants treated with 0.5 μL·L-1 C2H4 in the small-bud stage (largest buds 7 to 13 days from anthesis) than for plants treated in the medium-bud stage (largest buds 3 to 4 days from anthesis) or large-bud stage (largest buds 1 day from anthesis). Application of 1 or 2 mm silver thiosulfate (STS) was as effective as 3 mm STS in reducing bud abscission on plants exposed to 0.5 μL·L-1 C2H4 in the small-bud stage. Treatment with 2 mm STS before C2H4 exposure increased the display life (number of days from anthesis of the first flower to senescence of the last flower) of `Andre' in all three developmental stages, but increased the display life of `Crimson Giant' only in the small bud stage. These results demonstrate that the response of Easter cactus to C2H4 is affected by cultivar, C2H4 concentration, stage of floral development at the time of C2H4 exposure, and STS pretreatment.

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Thomas H. Boyle and Alexander Idnurm

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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Charles L. Rohwer and Royal D. Heins

15 or 20 °C before a 70-d vernalization at 15 °C had a greater PFAP (78% to 81%) than plants grown under LD until vernalization (62% to 63%) ( Peters and Rünger, 1971 ). Hatiora × graeseri given 50 SD before vernalization for 60 d at 5 to 15 °C