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Greenhouse-grown `Bison' and `Doria' peppers (Capsicum annuum L.) were harvested when mature green (MG) (>95% surface green) or ripe (>95% of surface red or yellow). Both cultivars responded similarly to temperature and neither exhibited chilling injury (CI), as indicated by surface pitting, after storage at 13C for 1 or 2 weeks. Ripe peppers showed no CI when held at 1C for 1 or 2 weeks, while MG peppers exhibited CI after these treatments. Exposing MG peppers to 1C for 3 days caused CI and stimulated C2H4 (12.3x) and CO2 production (2.5x). In contrast, a similar exposure of ripe peppers did not cause CI but stimulated C2H4 (6.5x) and CO2 production (1.4x). It seems that CO2 and C2H4 production was stimulated by exposure to 1C, not necessarily by CI development. Our data question the physiological significance of elevated CO2 and C2H4 production in CI development. The observed tolerance of ripe peppers to 1C suggests that ripe greenhouse-grown peppers can be stored at temperatures lower than those currently recommended for bell peppers.
A video-imaging technique, using commercial software to process images obtained at 550 nm, was established to estimate chlorophyll content of cucumber fruit disks. The chlorophyll content of excised disks was extracted, determined, and regressed on the video-image grey level. They were linearly related. The change in grey level of the whole visible image accurately indicated the change of green color during fruit development on the vine and the loss of green color after 1 week of storage at 13C. The relationship of the chlorophyll content on grey level was quadratic for three imaging methods: 1) average grey level of the five disks; 2) average grey level of the whole cucumber image; and 3) average grey level of central one-third of the whole cucumber image. Chlorophyll content was most highly correlated to the grey level of the disks themselves (residual SD = 6.74 μg·cm-2), but this sampling technique was destructive. Both one-third of the fruit image (SD = 9.25 μg·cm-2) and the whole image (SD = 9.36 μg·cm-2) provided satisfactory precision. For simplicity, whole-fruit imaging is suitable for estimating fruit chlorophyll content and for quantifying fruit green color intensity. Potential use of this technique in product sorting and shelf life prediction of long English cucumbers is discussed.
A portable, nondispersive infrared (NDIR) gas analyzer was modified to measure the concentration of CO2 and water vapor in small gas samples. A 2-mL gas sample was taken from a series of sealed flasks partially filled with a saturated solution of chemicals known to produce various levels of relative humidity (RH). The modified NDIR instrument quantified water vapor content by its absorption at 2.59 μm. Peak height was displayed on a strip chart recorder and a standard curve constructed. At a specific temperature, the vapor pressure (VP) and vapor pressure difference (VPD) were calculated for sweet pepper (Capsicum annuum L., cv. Mazurka) fruit packed in trays that were covered with plastic films having several levels of perforations. Water loss from the fruit was highly correlated with VPD inside the packages. The modified NDIR instrument has an advantage over other instruments used to measure RH because it can rapidly and simultaneously determine the concentration of water vapor and CO2 in a single injection of a small gas sample.
Abstract
Dormancy of non-cooled Lilium longiflorum Thunb. cv. Ace bulbs was broken with GA3 (1000 ppm), while ABA (500 ppm) partially negated the effect of vernalization on dormancy breaking. Infusion of bulbs with GA3 or ABA had little effect on days to anthesis. Injections of GA3, GA4, or GA7 into shoots from non-cooled bulbs did not substitute for vernalization or affect days to anthesis. ABA injections into shoots from cooled bulbs partially negated the effect of vernalization and delayed anthesis. Injections of GA3 or GA7 into shoots from cooled bulbs decreased days to anthesis, while GA3, GA4 or GA7 increased plant height. ABA delayed anthesis and reduced stem elongation. The major effect of exogenous GA applications appears to stimulate bolting.
Abstract
Lilium longiflorum Thunb. cv. Nellie White shoots rapidly emerged and flowered when bulbs were given a 4.5°C/40 day treatment. However, GA levels in the bulbs did not increase during the 4.5°C/40 day cold storage, but increased afterwards in the greenhouse with a GA maximum 30 days past storage. ABA activity patterns were similar to GA. Bulbs first treated at 4.5°C/30 days and then followed by 21°C/30 days had higher GA activity and their shoots were slower to emerge and flower than those of bulbs first treated at 21°C/30 days then given 4.5°C/30 days. Bulbs from 4 harvest dates had greater GA activity in the inner scales while ABA activity was greater in the outer scales.
Various stem-training systems were applied to greenhouse-grown `Mustang' cucumber (Cucumis sativus L.) plants at two production stages. Training systems determined the number of stems per plant, orientation of laterals, and leaf: fruit ratio. Training systems permitting high canopy light penetration resulted in darker fruit and a longer shelf life. Shelf life was positively related to rapid fruit growth in Expt. 1 but not in Expt. 2. Training systems to achieve a long shelf life of greenhouse-grown long English cucumber are described.
In commercial production of greenhouse cucumber, moderate water stress is often undetectable until plants show severe wilting. The purpose of this study was to establish a noncontact, early detection method for such moderate stress before visual wilting takes place. An infrared imaging system including an infrared camera, a personal computer, and necessary image processing software was placed in a greenhouse with the camera elevated and viewing the plant canopy. Selected plants, each in a bag of sawdust growing medium, were subjected to water stress by removing irrigation tubes from the growing medium. The infrared images obtained from a crop canopy displayed an increase in foliar temperature of stressed plants, which were located among normally watered (control) plants in the same greenhouse. Increased foliar temperatures of stressed plants occurred 1 to 3 days before wilting was observed. When visual wilting occurred, the stress treatment was stopped and irrigation was resumed within the same day. Cucumber plants showed no crop loss after one cycle of moderate stress. Repeated moderate stress caused yield loss. The potential applications of this nondestructive, noncontact detection method in plant science research and in commercial greenhouse production will be discussed.
Abstract
High temperature tended to aggravate injury caused to tomato plants by flooding. Based on plant responses such as chlorosis, epinasty, and wilting, less than 0.2% (8 of 4630 accessions) of the world collection of the garden tomato (Lycopersicon esculentum Mill.) and related Lycopersicon species exhibited some level of tolerance to a short period of flooding associated with high temperature. The level of flood tolerance in one of the 8 flood tolerant accessions, L-123, was found to be less than that of 7 other vegetables tested.
Design modification of a particle inflow-type gun for particle bombardment significantly simplifies construction and reduces fabrication time. The gun consists of a high-speed electric solenoid valve mounted on and through a vacuum jar. DNA-coated tungsten particles are placed on the support grid of a filter housing and accellerated by a burst of pressurized helium, which is controlled by a timer. Specimens are held between plastic screens and their distance from the particle support grid is adjusted with a miniature laboratory apparatus positioner. Transient expression of GUS in cantaloupe cotyledons and grape somatic embryos was equivalent to that obtained with a conventional particle inflow gun. The device was constructed with locally-available hardware in 40 minutes using a hand drill, some thread taps and a thread die.