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