the ACP into growing areas. This protected cultivation system works by physically excluding contact between the ACP and trees. One of the main advantages of this system is that there is reduced reliance upon frequent insecticide sprays to control
Abstract
A simple temperature control system constructed from a $10 homemade, precise, solid-state, proportional thermoregulator, resistive heating element, and insulated enclosure is described. It is intended as one of a series of small heated units, each set to a different temperature and placed in a single, large, refrigerated area, such as a large cooler or air-conditioned room, but can be modified for cooling in a heated area. Its demonstrated temperature control precision over 24 hr was ± 0.02°C at the thermal sensor at a set point of 25° and ambient of 19° ± 2.5°. Control temperature precision, range, and span are determined by thermoregulator components, enclosure construction, and ambient conditions. This or similar systems have been used successfully in seed germination, postharvest, cell culture, and nutrient release studies.
117 ORAL SESSION 34 (Abstr. 241-246) Vegetables: In Life Support Systems
Chambers were constructed to measure gas exchange of entire potted grapevines (Vitis vinifera L.). The plant enclosures were constructed from Mylar film, which is nearly transparent to photosynthetically active radiation. Maintaining a slight, positive, internal pressure allowed the Mylar chambers to inflate like balloons and required no other means of support. The whole-plant, gas-exchange chamber design and construction were simple and inexpensive. They were assembled easily, equilibrated quickly, and did not require cooling. They allowed for the measurement of many plants in a relatively short period. This system would enable the researcher to make replicated comparisons of treatment influences on whole-plant CO2 assimilation throughout the growing season. While CO2 measurement was the focus of this project, it would be possible to measure whole-plant transpiration with this system.
The effects of four propagation moisture management systems on the water relations and rooting of cuttings of three tropical woody crops were investigated at a relatively cool, but high irradiance site. Leafy semihardwood or leafless hardwood cuttings of Bougainvillea × Buttiana Holtt. & Standl. (bougainvillea), and leafy semihardwood cuttings of Hibiscus rosa-sinensis L. (hibiscus), and Dovyalis caffra (Hook. f. et Harv.) Warb. (kei apple) were propagated in shade under contact tent polyethylene enclosures or in the open with or without intermittent mist. Xylem water potential and leaf and air temperatures and relative humidity were monitored during the rooting period. Hardwood cuttings rooted better than softwood cuttings of bougainvillea. The best rooting of softwood cuttings of all three species was consistently associated with contact polyethylene, whereas open-propagated, nonmisted cuttings rooted poorly or not at all. The poor rooting of open-propagated nonmisted cuttings was associated with the most negative midday ψ and the greatest water vapor density deficit of air surrounding the cuttings (VDDA), but ψ and VDDA were otherwise not consistently associated with success of rooting in other treatments. Midday ψ of cuttings under contact polyethylene was either less negative or not different from that of other treatments despite the fact they exhibited the greatest daytime leaf and leaf to air temperature differences. Because ambient night temperatures were suboptimal for rooting, the warm air trapped beneath the polyethylene enclosures at night may have contributed to improved rooting in these treatments.
Abstract
The young developing leaves of 20-day-old lettuce plants (Lactuca sativa L. ‘Buttercrunch’) were enclosed by aluminized polyethylene sheaths to decrease transpiration and reduce Ca transport. The plants were grown in recirculating solution culture systems using a modified half-strength Hoagland’s solution under cool-white fluorescent lamps with a photosynthetic photon flux of 350 μmol·s−1·m−2 in a 16:8-hr (light:dark) period. Air temperature and humidity were 20°C and 65%, respectively. After 4 days of enclosure, 53% of the inner leaves (leaves one to 3 cm in length) were tipburned. After the same period, less than 1% of the inner leaves on control plants were tipburned. The concentration of Ca in enclosed inner leaves was 0.63 mg·g−1 dry weight, compared to 1.48 mg·g−1 dry weight in inner leaves that were not enclosed. The Ca concentration in transpiring outer leaves of all plants was 9.9 mg·g−1 dry weight. The Mg concentration in enclosed inner leaves was 2.25 mg·g−1 dry weight, compared to 2.34 mg·g−1 dry weight in inner leaves that were not enclosed. This research documents that enclosure of leaves at the growing point, as would occur with normal head development, is sufficient to create a limiting concentration of Ca in the enclosed tissue and encourage tipburn development.
A monitoring and control system for sequentially measuring whole-tree-canopy gas exchange of four apple (Malus domestica Borkh.) trees in the field is described. A portable, highly transparent, open-top whole-canopy cuvette was developed for complete enclosure of the above-ground portion of the tree. The flux of whole-canopy CO2 and H2 0 vapor was estimated from differential CO2 concentration and H2O-vapor partial pressure between ambient/reference air entering the cuvette and analysis air leaving the cuvette, as measured by infrared gas analysis. The bulk air-flow rate through the chamber was measured with a Pitot static tube inserted into the air-supply duct and connected to a differential pressure transducer. Performance of the whole-canopy cuvette system was tested for its suitability for gas-exchange measurements under field conditions. The air flow through the whole-canopy cuvette was 22000 L·min-1 (≈5.5 air exchanges/min) during the day, providing adequate air mixing within the cuvette, and 4000 L·min-1 (≈1 air exchange/min) during the night. Daily average leaf temperatures within the cuvette were 2-3 °C higher than to those on trees outside the cuvette. Photosynthetic photon flux transmitted through the chamber walls was at least 92 % of the incident ambient radiation. Moreover, the whole-canopy cuvette was evaluated without tree enclosure to determine the degree of “noise” in differential CO2 concentration and H2O-vapor partial pressure and was found to be acceptable with ΔCO2 ± 0.3 (μmol·mol-1 and ΔH2O ± 5 Pa. Whole-canopy carbon gas exchange and transpiration of four cropping `Braeburn'/M.26 apple trees followed closely incident radiation over the course of a day.
Greenhouse and field methods were developed to screen Allium spp. for resistance to Botrytis leaf blight (caused by Botrytis squamosa Walker). In the green-house, plants were sprayed with laboratory-grown inoculum and incubated in a temperature-controlled enclosure containing an atomizing mist system. For field inoculations, a portable misting system with windbreaks was erected, and the plants were sprayed with laboratory-grown inoculum. Greenhouse and field incubation conditions maintained leaf wetness without washing inoculum from the leaves. Botrytis leaf blight symptoms in greenhouse and field evaluations were identical to symptoms in commercial onion fields. A total of 86 selected USDA Allium collection accessions were evaluated using these methods. All A. fistulosum accessions and A. roytei were highly resistant to immune, as were most accessions of A. altaicum, A. galanthum, A. pskemense, and A. oschaninii. Nearly all of the A. vavilovii and A. cepa accessions were susceptible. However, one A. cepa accession (PI 273212 from Poland) developed only superficial lesions, which did not expand to coalesce and blight leaves. This work confirms previous reports of Botrytis leaf blight resistance in Allium spp., and suggests that strong resistance exists with A. cepa.
(Landmark Plastics). Cuttings were placed inside a 4-ft-wide by 8-ft-long by 3-ft-high polyethylene-covered enclosure on top of a 3-inch layer of moistened pine bark (to maintain high humidity) within a double-layer, polyethylene-covered greenhouse at the
During the past century, horticulturists have investigated various systems to propagate plants from stem cuttings. Initially, cutting propagation involved inserting cuttings into soil within a high-humidity enclosure ( Bailey, 1896 ). However, high