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  • Author or Editor: L. Zhang x
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Abstract

Effects of a wet tent (cloth continuously wetted), an intermittent mist, and a shade system were examined for establishment, survival, and growth of microcuttings of three cultivars of Euphorbia fulgens Karw. ex Klostch. The wet tent system resulted in high survival rates and rapid plantlet growth. Microcuttings placed in the mist system had survival rates close to that in the wet tent, but had the poorest plantlet growth. Microcuttings placed directly in the shade had a poor survival rate, but plantlets that survived grew as well as those from the wet tent. In all three acclimatization systems, microcuttings of the white cultivar had the highest survival rate; those of the orange and red cultivars were second and third, respectively. No difference was found in plantlet growth among the surviving cultivars after removal from treatment in acclimatization systems. Microcuttings 41 to 50 mm long survived best; survival rate increased with microcutting length. The minimum microcutting length for satisfactory survival rates (79%) was 31 mm. Microcuttings rooted a month earlier than did conventional stem-tip cuttings in the wet-tent system.

Open Access
Authors: and

Abstract

Effects of trans-zeatin, sucrose, myo-inositol, and medium pH on shoot proliferation of Euphorbia fulgens Karw. ex Klostch were studied in vitro. Maximum shoot production occurred on media supplemented with 5 μΜ zeatin, but maximum shoot length with 5 to 15 μΜ. Shoot production increased with sucrose concentration, and was maximal at 131.5 mM. myo-lnositol concentration up to 0.6 mM did not have a significant effect on shoot production, but >1.1 mM reduced it. The optimal medium pH was 5.3 for shoot proliferation, but lower pH values stimulated shoot growth. Chemical names used: trans-2-methyl-4-(1H-purin-6-ylamino)-2-buten-l-ol (trans-zea-tin), α-D-glucopyranosyl-β-D-fructofuranoside (sucrose).

Open Access
Authors: and

Application of entomopathogenic fungi by inundative releases has been attempted for control of a wide range of insect pests, with generally poor results. This is largely because entomopathogens are often treated as direct substitutes for chemical insecticides and applied without an adequate knowledge of their interactions with the local environment. Humidity of greater than 90% RH has long been regarded as the a critical condition for germination and infection by the spores. With both temperature and humidity controlled, greenhouse crops offer an excellent potential for pest control using entomopathogens. The long-term maintenance of >90% RH, however, is not standard practice in greenhouse production. This study explored the possibility of improving the efficacy of the fungi by temporarily changing greenhouse humidity without adversely affecting crop growth. The study included laboratory and greenhouse trials. In laboratory trials, four humidity levels of 75%, 80%, 89%, and 97.5% RH were evaluated over a 48-h period. Three commercial products of Beauveria bassiana were evaluated (Naturalis-O, Botanigard 22 WP, and Botanigard ES). Greenhouse pests of green peach aphid, melon aphid, western flower thrips, whitefly, and two-spotted spider mite were used as target insects. The infection rate of B. bassiana was found to increase when the sprayed adult insects were exposed to higher humidity levels with the maximum infection obtained at 97.5% RH. Percent infection and difference between humidity levels, however, were formulation- and host-dependent. The highest overall control efficacy was obtained by using Botanigard ES. Botanigard ES was highly effective to adult green peach aphid, melon aphid, and greenhouse whitefly at high humidities. Effects of B. bassiana against biological control agents for greenhouse vegetable crops were also evaluated. Greenhouse trials were conducted in two adjacent greenhouse compartment with high and low humidity conditions for 48 h, respectively, for selected pest insects to valid laboratory results.

Free access
Authors: and

This study investigated greenhouse and plant surface microclimate for cucumber crops (Cucumis sativus) under high pressure overhead fogging. Overhead fogging maintained greenhouse humidity above its set point and avoided excessively low humidity conditions on sunny days. Fogging caused minimal to moderate changes in greenhouse air temperature in the fall depending on whether or not the leaves were sunlit or shaded. The temperature of sunlit leaves decreased by 1 to 1.5 °C (1.8 to 2.7 °F) under occasional fogging in the morning and by 3 °C (5.4 °F) under extensive fogging during noon hours. The temperature of fogged shaded leaves did not significantly change (<1 °C) when compared to nonfogged shaded leaves. Leaf wetness duration (LWD) was extended when overhead fogging was used. The length of extended daytime wetness duration (LWDday) from 0800 to 1700 HR in the fogged greenhouse depended primarily on global radiation at the leaf level. A simulation model was developed to predict LWDday using daily integrated global radiation (Rsum) as the input.

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Abstract

The dorsal (lower) surfaces of leaf samples taken from 38 species of Camellia were examined for distinctive characters which might serve as an aid in taxonomic characterization of subgenera and sections in Camellia. A simple technique involving cyanoacrylate adhesives was used to prepare microscope slides for examination with a light microscope equipped with differential interference contrast optics. Specific characteristics studied included the distribution of stomata, the shape and size of guard, subsidiary, and other epidermal cells, and the presence or absence of epidermal hairs and gland and corky cells. Characteristics of epidermal cells on the dorsal surfaces of Camellia leaves can serve as a technique for the classification of species and cultivars and in the verification of species purity or determination of hybrid status.

Open Access

Overhead fogging or misting is an essential technique applied in modern greenhouses for cooling and humidifying. This technique can be used to promote yield and quality of greenhouse crops either by providing favorable environment for the plant growth or by increasing the efficiency of greenhouse pest and disease control. In this study, the effect of high-pressure overhead misting on greenhouse climate and leaf surface microclimate conditions for cucumber crops in a glass greenhouse was investigated. It was found that the temperature of the greenhouse air was lowered by 5-6 °C and relative humidity was increased by 20% to 30% during misting. The temperature of sunlit leaves was slightly reduced in the morning (2-3 °C), and leaf wetness duration was significantly extended by misting. Leaf wetness duration under misting was predominately influenced by light intensity at the leaf level and was modelled as a function of misting period and average radiation intensity. Results of this study can be used to improve the predictions of pest and disease breakout and the efficiency of their control measures. The empirical model developed in this study can be integrated with leaf surface microclimate models to correctly predict surface moisture conditions and evaporative cooling from water films at the leaf surface.

Free access

Phomopsis cucurbitae is a latent infecting pathogen that infects unripe muskmelon fruit, but causes decay after harvest. This fungus causes severe losses during muskmelon fruit storage and marketing in the U.S., Japan, and some Central American countries. Previous studies showed that the fungus produced the cell wall-degrading enzyme polygalacturonase (PG) in both culture and muskmelon fruit tissue. The role of P. cucurbitae PG in the fruit decay process and its relation to latent infection is not well-understood. A prominent PG isozyme produced by the fungus in decayed fruit was purified to homogeneity by a sequence of extraction, ultrafiltration, preparative isoelectric focusing, anion exchange, and gel filtration chromatography. This isozyme exhibited endo-activity, a molecular weight of 54 kDa according to SDS-PAGE, and a pI of 4.2 based on IEF-PAGE. Isozyme activity was optimal at 40–45°C and pH 5.0. It had a Km of 44.7 g/ml and a Vmax of 0.313. The purified isozyme also effectively macerated mature muskmelon fruit tissues. This isozyme was the most prominent of the PG isozymes produced by P. cucurbitae in decaying fruit, and may play an important role in postharvest decay.

Free access

We examined effects of single-layer glass and double-layer antifog polyethylene films on growth and flowering of stock (Matthiola incana L.) and snapdragon (Antirrhinum majalis L.) in a 3-year period. Stock produced more buds/spike with shorter but thicker stems under single-layer glass and under antifog 3-year polyethylene, and showed higher photosynthetic capacity (P c) under single-layer glass than under other covers regardless of light regimes. Similarly, growth and flowering of snapdragon were significantly better under single-layer glass than in polyethylene houses. A supplemental light of 60 μmol·m-2·s-1 accelerated flowering by 20 to 25 days, improved flower quality, and eliminated differences in plant growth and quality of snapdragon between covering treatments. The P c of stock was lower under all polyethylene covers than under single-layer glass. Among the three antifog polyethylene films, a slightly higher P c was measured for plants under antifog 3-year polyethylene. However, there was no difference among covering treatments in the net photosynthetic rate (P N) at low light level (canopy level). Supplemental lighting reduced P c of stock leaves, especially under single-layer glass, and diminished differences in P c among covering treatments. Dry mass was more influenced by larger leaf area caused by higher leaf temperature than by P N. Overall, antifog 3-year polyethylene was a good covering material when both plant quality and energy saving were considered.

Free access

Abstract

Nodal sections of actively growing apical shoots from greenhouse-grown plants of Euphorbia fulgens Karw. ex Klotsch initiated new shoots after 4 weeks on a modified Murashige and Skoog (MS) medium supplemented with 9.1 μm zeatin. When cultures from the initiation stage were transferred for proliferation to the same medium, up to 14 shoots 5 mm long or longer were obtained per culture 4 weeks later. Through subcultures, 40 transplantable shoots per explant could be produced within 12 weeks. Shoots were rooted in vitro in the greenhouse with satisfactory survival rates. Chemical names used: (E)-2-methyl-4-(1H-purin-6-ylamino)-2-buten-1-ol (zeatin).

Open Access

Plants to be screened for resistance to mechanically transmitted viruses can be inoculated by using an inexpensive electric-powered leaf blower. This device greatly reduces the amount of time to inoculate large populations when compared with hand-rubbing methods. No significant differences were noted with regard to the frequency of seedlings that escaped infection.

Free access