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  • Author or Editor: D. W. Buchanan x
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Abstract

This symposium sponsored by the American Society for Horticulturural Sciences and the American Society for Plant Physiologists is an effort to integrate plant microclimate and stress physiology research. The symposium was jointly organized by the Climatology and Meteorology and Developmental and Stress Physiology working groups. One objective is to discuss the proper instrumentation, its use, data acquisition storage and retrieval techniques for monitoring the plant microclimates and responses to changes in the environment, such as stress.

Open Access

Abstract

Budbreak of ‘Woodard’ and ‘Bluegem’ rabbiteye blueberry (Vaccinium ashei Reade) occurred sooner than ‘Tifblue’ following chilling at constant 10 and 15°C and a diurnal regime of 8 hours at 15°/16 hours at 7°. Results indicate a narrower range of effective chilling temperatures for ‘Tifblue’. The temperature effect was more pronounced for ‘Woodard’ rooted cuttings than budsticks and was more significant for floral than vegetative budbreak. Floral budbreak of rooted cuttings subjected to 14 days at 30° in the middle of the chilling period was faster than at continuous chilling treatments. The number of days required for budbreak was significantly reduced as chilling hours increased.

Open Access

Abstract

Evaporative cooling by overhead sprinkling during rest advanced bloom of ‘Sungold’ nectarine [Prunus persica (L.) Batsch] about 11 days. The bloom advance was due to water applied to the canopy and not to increased water in the root zone. A rest prediction model for low chilling nectarines which accurately predicted rest completion for all unsprinkled treatments failed to predict the date of rest termination for sprinkled treatments, suggesting other factors are involved in addition to temperature.

Open Access

Abstract

Floral bud break of 1-year-old rooted cuttings of ‘Sungold’ nectarine (Prunus persica (L.) Batsch) was observed following chilling at constant and diurnal temperature regimes. Continuous exposure to 10°C was as effective as 7°. Rate of bud break increased as chilling increased up to 750 hours. Floral bud break of plants exposed to 14 days at 30° during the middle of the chilling period was more rapid but failed to reach the level of activity of plants exposed to constant temperatures. A chill unit model developed for ‘Sungold’ nectarine which has a chilling requirement of 550 hours indicated a broader range of effective temperatures and a higher optimum for rest completion as compared to the Utah model and predicted rest completion more accurately than other methods when applied to orchard temperature data.

Open Access

Abstract

2-Chloroethane-phosphonic acid (CEPA), applied as a spray to 5-year-old ‘Maygold’ peach trees in the 80% to full bloom stage, effectively thinned blossoms and young fruit and was accomplished without severe gumming or dwarfing of subsequent vegetative growth. The reaction time required to obtain abscission (9 days) indicated that CEPA interfered with processes leading to sexual fertilization. Laboratory studies of the influence of CEPA and ethylene on pollen germination and pollen tube growth indicated that these 2 processes were not inhibited, except from exposure to high concentrations (100 to 1000 ppm) for several hours. At low concentrations (.01 to 10 ppm) both processes were stimulated.

Open Access

Abstract

Development from free nuclear to completely cellular endosperm was observed in ‘Flordasun’ and ‘Early Amber’ peaches and ‘Sunred’ nectarine. The free nuclear stage was present at 33, 38 and 49 days before first harvest, respectively, after which cytokinesis began. Approximately a third of the fruit had completely cellular endosperm at 23, 32 and 43 days before first harvest, at which times seed lengths and fruit diameters were 13.5 and 24.1 mm, 13.2 and 22.9 mm, and 11.4 and 20.5 mm, respectively. During cytokinesis, fruit and seed sizes were larger in the varieties with a shorter developmental cycle. Endosperm was completely cellular in all fruit of each variety at 19, 30 and 39 days and early stages of stone hardening was observed at 21, 30 and 43 days before first harvest. Seed length, fruit diameter and fruit volume were highly correlated within each variety and these parameters were related to the stages of endosperm development.

Open Access

Abstract

‘Maygold’ and ‘Q310-7’ peaches were thinned adequately with 300 to 400 ppm N-l-naphthylphthalamic acid (NPA) applied at full bloom; ‘Armgold’ was not satisfactorily thinned. ‘Early Amber’ was thinned when NPA was applied 5 days after full bloom. Optimum time of chemical thinning was affected by the length of the bloom period.

Open Access

Abstract

A computer-controlled temperature chamber system using modified chest-type freezers was developed for plant chilling studies. A temperature range of −18° to 35° ± 1.25°C enabled the system to be used for cold hardiness research. Chambers were easily modified for accurate control of soil temperature of container-grown plants. This system provided flexibility of use and regulation of several temperature regimes simultaneously at a comparatively low cost.

Open Access

Abstract

The development of the endosperm of the ‘Maygold’ peach may be used to predict the optimum time for chemical thinning. With this variety 3-chlorophenoxy alpha-propionamide (CPA) was most effective when fruit diameter and seed length were 24 and 13-14 mm, respectively. This stage occurred 29 days after full bloom when cytogenesis was completed in 35 per cent of the fruit.

Open Access

Abstract

Drip irrigation applied to cultivars of rabbiteye blueberry (Vaccinium ashei Reade) maintained soil moisture at 25 to 35%, (volume basis), –0.07 bars soil-water potential while no irrigation resulted in 12.5% soil moisture, –2 to –3 bars. Irrigation reduced leaf diffusive resistance (rL) by 50% and increased transpiration (T) by 70% but had no significant effect on midday stem xylem pressure potentials (ψx ). Both yield and berry weight from irrigated plots were increased from 20 to 25% over those on nonirrigated plots. Seasonal changes in ψx , rL, and T of nonirrigated bushes suggested this species has some characteristic adaptations to drought conditions, one such adaptation being wax rodlets observed in and adjacent to stomatal pores. These may have contributed to a favorable water balance under stress by increasing leaf diffusive resistance.

Open Access