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Thomas H. Boyle

Binomial probability distributions were used to determine the effects of percent seed germination and number of seeds sown per cell on expected numbers of seedlings in plug trays. Expected numbers of empty cells in five types of plug trays (128, 273, 338, 406, and 512 cells/tray) were calculated for cases where one to seven seeds were sown per cell and seed germination ranged from 50% to 95%. Generally, one additional seed was required per plug cell for each 10% decrease in the germination percentage in order to attain the same number of filled cells per plug tray. Expected frequencies were calculated for the number of seedlings in plug trays when one to five seeds were sown per cell and seed germination ranged from 50% to 95%. When the number of seeds sown per cell remained constant, uniformity in seedling number per cell increased as the germination percentage increased. When percent seed germination remained constant and the number of seeds sown per cell was increased, the percentage of cells with at least one seedling increased, whereas the uniformity in seedling number per cell decreased. Additional examples are presented in the article on the utility of binomial distributions in determining expected number of seedlings.

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Thomas H. Boyle

Rhipsalidopsis (Easter cactus) and Schlumbergera (Thanksgiving and Christmas cactus) are two genera of epiphytic cacti endemic to southeastern Brazil. Rhipsalidopsis is comprised of two species (R. gaertneri and R. rosea) and Schlumbergera contains five species (S. opuntioides, S. obtusangula, S. orssichiana, S. russelliana, and S. truncata). There is considerable potential for the improvement of commercial cultivars in both genera. Flower color and form, plant habit, postharvest performance, and the responsiveness to floral induction treatments are selection criteria used in breeding of Rhipsalidopsis. The selection criteria used in breeding of Schlumbergera are flower color and form, growth rate, phylloclade size and shape, plant habit, and the critical daylength for flowering. Inbreeding depression, self-incompatibility, and a long generation time (1.5 to 3 years) are impediments to breeding in both genera. Interspecific hybridization has been performed in Rhipsalidopsis and Schlumbergera, and significant phenotypic variation has been observed within interspecific hybrid populations.

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Thomas H. Boyle

Rhipsalidopsis (Easter cactus) and Schlumbergera (Thanksgiving and Christmas cactus) are two genera of epiphytic cacti endemic to southeastern Brazil. Rhipsalidopsis is comprised of two species (R. gaertneri and R. rosea) and Schlumbergera contains five species (S. opuntioides, S. obtusangula, S. orssichiana, S. russelliana, and S. truncata). There is considerable potential for the improvement of commercial cultivars in both genera. Flower color and form, plant habit, postharvest performance, and the responsiveness to floral induction treatments are selection criteria used in breeding of Rhipsalidopsis. The selection criteria used in breeding of Schlumbergera are flower color and form, growth rate, phylloclade size and shape, plant habit, and the critical daylength for flowering. Inbreeding depression, self-incompatibility, and a long generation time (1.5 to 3 years) are impediments to breeding in both genera. Interspecific hybridization has been performed in Rhipsalidopsis and Schlumbergera, and significant phenotypic variation has been observed within interspecific hybrid populations.

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Thomas H. Boyle

Allotetraploid Z. angustifolia × Z. elegans hybrids (2 n =46) were reciprocally backcrossed to Z. angustifolia (2 n = 22 or 44) and Z. elegans (2 n = 24 or 48). Pollen germination and pollen tube penetration of the stigmatic surface were observed for all 8 cross combinations. At 14 days after pollination, the percentage of florets with embryos ranged from 0 to 69%, and some hybrid embryos exhibited developmental abnormalities. Seed-propagated backcross (BC1) populations were generated with Z. angustifolia (2 n =44)as ♀ or ♂, and Z. elegans (2 n =48) as ♀ BC1 progeny from these 3 crosses demonstrated low to high levels of resistance to bacterial leaf and flower spot (incited by Xanthomonas campestris pv. zinniae) and high levels of resistance to powdery mildew (incited by Erysiphe cichoracearum). BC1 hybrids derived from crossing allotetraploid hybrids as ♀ and Z. elegans (2 n =48) lines have commercial potential as disease-resistant, flowering annuals.

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Thomas H. Boyle

Flowers of two cacti [Hatiora gaertneri (Regel) Barthlott `Crimson Giant' and Schlumbergera truncata (Haworth) Moran `Eva'] were pollinated at different times between anthesis and senescence to determine the effect of floral age on seed production. Studies were conducted in a growth chamber (20 ± 0.5°C) to minimize temperature effects. Mean flower longevity (time from anthesis to first signs of senescence) was 4.7 days for S. truncata and 10.5 days for H. gaertneri. Stigmas of both species were receptive to pollination on the day of anthesis. The maximum number of viable seeds per pollinated flower was obtained when flowers of S. truncata and H. gaertneri were pollinated (respectively) on the second and fourth days after anthesis. For both species, the relationship between floral age and number of viable seeds per pollinated flower was described by a second-degree polynomial. The rate of pollen tube growth in the style was about 1.7 mm·h–1 for S. truncata and about 0.9 mm·h–1 for H. gaertneri. Some senesced flowers of H. gaertneri were capable of setting fruit with viable seed. Flowers of S. truncata did not set fruit when pollinated during the late phase of flower opening or after they had senesced. Senesced flowers of S. truncata failed to set fruit due to an insufficient number of pollen tubes reaching the ovary.

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Thomas H. Boyle

Dwarf Easter cactus [Rhipsalidopsis rosea (Lagerheim) Britton and Rose] plants were subjected to temperature and photoperiod treatments to determine their influence on flowering. All plants exposed to 10C at night (NT) and natural daylengths (ND) during winter and spring for 4 or more weeks flowered, whereas some plants grown continuously under 18C NT and either long days [(LD) provided by incandescent irradiation] or ND failed to flower. Days to flowering and number of flower buds per plant increased linearly as the duration of exposure to 10C NT and ND increased from 4 to 16 weeks. The number of flower buds were greatest on plants receiving either continuous 10C NT or 12 to 16 weeks 10C NT, then 18C NT until flowering. Plants receiving 18C NT flowered earlier under LD than ND when treatments followed 4 or 8 weeks-of 10C NT and ND.

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Thomas H. Boyle

The effects of BA concentration on flowering and dry-matter partitioning in shoots of `Crimson Giant' Easter cactus [Rhipsalidopsis gaertneri (Regel) Moran] were investigated. Treatments were applied 12 days after starting the forcing phase (before flower buds were visible) and included BA at 0, 10, 50, 100, and 200 mg·liter–1. Relative to the controls, BA increased the total number of flower buds per plant and delayed flowering by 2 to 3 days. The percentage of aborted flower buds increased more than 3-fold as BA concentration increased from 0 to 50 mg·liter–1 and increased further when 100 or 200 mg·liter–1 was applied. The number of flower buds that reached anthesis increased quadratically with increasing BA concentration and was maximal when plants were treated with 50 mg·liter–1. As BA concentration increased from 0 to 200 mg·liter–1, total dry weight of phylloclades decreased, whereas dry weight of floral tissue increased by a nearly equivalent amount. BA increases flowering and alters partitioning of dry matter in reproductive plants of `Crimson Giant'. Chemical name used: N-(phenylmethyl)-1H-purine-6-amine (BA).

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Thomas H. Boyle

The effects of temperature and clonal genotype on flowering of Easter cactus (Rhipsalidopsis Britton & Rose) were investigated in two experiments. Plants of `Crimson Giant', `Evita', `Purple Pride', and `Red Pride' were exposed to 6 weeks of either 10C or 18C night temperature (NT) under 9- to 9.5-hour natural daylengths (ND), and afterwards were forced at 18C NT and long days (LD). All clones produced fewer flowers when exposed to 18C and ND as compared with 10C and ND; however, the clones varied significantly in their flowering responses. Relative to 10C NT and ND, exposure to 18C NT and ND resulted in an 84% to 95% decrease in the number of flower buds for `Evita', `Purple Pride', and `Red Pride', but only a 50% decrease in the number of flower buds for `Crimson Giant'. In another experiment, 23 clones were exposed to 18C NT and 8-hour short days for 6 weeks, then forced at 18C NT and LD. The clones exhibited differences in percentage of plants flowering, days to flowering, percentage of apical phylloclades flowering, and number of flower buds. `Crimson Giant' outperformed all other clones. Further breeding and selection may yield genotypes that flower more prolifically at 18C minimum than current cultivars.

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Thomas H. Boyle

The objective of this study was to determine the effects of temperature, relative humidity (RH), and storage duration on moisture content and viability of Schlumbergera truncata (Haworth) Moran (Thanksgiving cactus) pollen. Pollen viability was assayed by the fluorochromatic reaction (FCR) test, percentage fruit set, and numbers of viable seeds per fruit. Pollen moisture content was ≈38% at anthesis but decreased to ≈12% by 1 day after anthesis and remained low (10% to 12%) until flowers senesced. Pollen viability was 85% on the day of anthesis, remained at ≈80% from 1 to 3 days after anthesis, and decreased to ≈65% when flowers began to senesce. When pollen was stored for 4 days at 21 °C, moisture content decreased to 1% for pollen stored at 1% RH but increased to 33% for pollen kept at 100% RH. Fruit and seed yields obtained with pollen stored for 4 days at 21 °C and 15%, 28%, or 52% RH did not differ significantly from those obtained with fresh pollen. Pollen stored for 4 days at 21 °C and 1%, 68%, or 90% RH produced fewer fruit and seeds than fresh pollen. Fruit and seed yields obtained with pollen stored 20 days at 21 °C and 15% or 28% RH were similar to yields obtained with fresh pollen. Pollen with ≤23% moisture content that was stored at -18 °C for ≥24 hours retained its original viability (≈85%) whereas pollen with a high (32% to 34%) moisture content exhibited low (≈22%) viability after storage at -18 °C for ≥24 hours. Pollen stored for 140 days at 4 or -18 °C and 13% to 51% RH yielded as many viable seeds per fruit as fresh pollen. Although S. truncata pollen is tricellular, it tolerates desiccation to a low (4%) moisture content and can be stored at temperatures below 0 °C.

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Thomas H. Boyle

True-breeding lines of Zinnia marylandica Spooner, Stimart and Boyle [allotetraploids of Z. angustifolia H.B.K. and Z. violacea Cav. (2n = 46)] were reciprocally backcrossed with diploid and autotetraploid forms of Z. angustifolia (2n =22 or 44) and Z. violacea (2n =24 or 48). In most cases, backcrosses were more successful with Z. angustifolia and Z. violacea as autotetraploids than as diploids. Seed-generated, backcross (BC1) families were obtained by crossing Z. marylandica (as female) with autotetraploid Z. angustifolia or autotetraploid Z. violacea. BC1 plants were phenotypically intermediate between the two parental lines for most morphological characters. Crosses between Z. marylandica and autotetraploid Z. angustifolia yielded BC1 plants with 33% stainable pollen, whereas crosses between Z. marylandica and autotetraploid Z. violacea yielded BC1 plants that produced malformed, poorly-stained pollen. No embryos were observed in capitula collected from field-grown BC1 plants. BC1 hybrids of Z. marylandica and autotetraploid Z. violacea produced larger capitula and more ray florets than Z. marylandica, and exhibited novel combinations of floral pigments not observed in Z. marylandica ray florets. BC1 hybrids of Z. marylandica and Z. violacea have commercial potential as seed-propagated, bedding plants.