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  • Author or Editor: C. Fred Deneke x
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Vegetative growth and flowering of Mandevilla `Alice du Pont' in response to foliar-applied uniconazole were determined in 3 experiments. Plants pruned to 2 nodes were treated with foliar applications of 30, 60, 90, and 120 ppm uniconazole. All uniconazole rates induced temporary leaf cupping and suppressed growth excessively for at least 6 weeks; thereafter, plants grew similarly to the control. Single applications of 5, 10, 15, and 20 ppm uniconazole were not effective in controlling vegetative growth, but multiple applications of 5.0, 7.5, 10.0, 12.5, 15.0, 17.5, and 20.0 ppm uniconazole provided acceptable, but not excessive, suppression of internode elongation. As the concentration of uniconazole increased, the interval between applications increased. Flowering was delayed and bloom size was reduced as uniconazole rate increased.

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Tissue-cultured plugs of Nandina domestica Thunb. `Hat-hour Dwarf' and `San Gabriel' were grown in 1.5-liter pots under 30%, 47%, or 62% shade. After 20 weeks, plants were moved to a simulated consumer environment (SCE) maintained at 21C, ≈60% relative humidity, and a 12-hour photoperiod with an irradiance of 7 μmol·m -2·s-1. Final quality ratings (after 35 weeks in the SCE) for both cultivars were good, but the plant quality of `San Gabriel' declined more quickly than that of `Harbour Dwarf'. Final quality rating of `Harbour Dwarf' grown under the highest percentage of shade was higher than that of plants grown under 30% or 47% shade; production shade percentages had no influence on the final quality rating of `San Gabriel'. Plants (of both cultivars) grown in 0.6-liter (11-cm-diameter) pots were test-marketed through six supermarket floral departments and captured 16% of total 10- to 11-cm-size foliage plant sales. Sixty percent of consumers indicated the plant's “newness” as the primary consideration for its purchase. These two N. domestica cultivars could be marketed successfully as interior foliage plants.

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The postharvest quality of regal pelargoniums [Pelargonium × domesticum L. H. Bailey] is limited by petal abscission. Cultivars that have diverse postharvest longevities were selected to study ethylene sensitivity and endogenous ethylene production. Petals of both intact and detached inflorescences abscised in response to low dosages of exogenous ethylene (0.5 μl·liter-1 for 1 hour). Ethylene sensitivity varied among cultivars and increased with floret age. Silver thiosulfate reduced ethylene sensitivity and often extended floret longevity beyond that of the controls. A climacteric-like rise in endogenous ethylene production occurred in excised gynoecia (including the receptacle) as floret age increased from 1 to 12 days postanthesis. Ethylene production increased a few days earlier and achieved a higher maximum rate in `Parisienne' than in `Virginia'; `Parisienne' also abscised petals earlier. Relatively low levels of endogenous ethylene may regulate petal abscission, since inflorescences were very sensitive to exogenous ethylene, and increased endogenous ethylene production preceded petal abscission.

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The root rot fungus Phytophthora parasitica is known to be very destructive to annual vinca (Catharanthus roseus). Phytophthora produces motile zoospores which swim freely in water, posing a special threat to crops grown using a recirculating water supply. Vinca were transplanted into 7 cm square pots containing a sphagnum peat:perlite medium. The medium was inoculated with the pathogen and plants were then placed in one row on each ebb and flow bench. Untreated vinca were placed in six additional rows on the benches. Separate benches were used to space plants at a distance of either 1 cm or 4 cm between pots. Plants were harvested biweekly over a six week period and tested for presence of Phytophthora. Cumulative results of root sampling revealed pathogen movement to 60% of untreated plants spaced at 1 cm, and to 30% of those spaced at 4 cm. Severe root injury (injury to root system ≥ 25%) was exhibited in 36% of the closer spaced plants, compared to 13% of those spaced at 4 cm. Phytophthora zoospores were detected in one tank which was used to irrigate plants spaced at 1 cm. Closer plant spacing enhanced the pathogen's ability to infect healthy plants.

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