Four film-forming antitranspirants, Vapor Gard, Envy, Wilt-Pruf, and Folicote, and a new metabolic antitranspirant UC86177 were applied to container-grown Ulmus parvifolia Jacq. (Chinese elm), Malus sargentii Rehd. (Sargent's crabapple), Viburnum plicatum tomentosum Thunb. (doubleflle viburnum), Lycopersicon esculentum Mill. `Early Giant' (tomato), Petunia × hybrids Hort. Vilm-Andr. `Royal Pearls' (petunia), and Impatiens wallerana Hook. f. `Blitz Orange' (impatiens) plants. Water status was assessed by the following methods: transpiration as water loss per unit leaf area, wilt by visual evaluation, and xylem pressure potential (XPP) determined with a pressure chamber. Antitranspirant treatment had no beneficial effect on water status of doublefile viburnum. In comparison to control plants, results of wilt ratings, XPP, and transpiration measurements for the elm, crabapple, tomato, petunia, and impatiens plants can be summarized as follows: UC86177-treated plants showed significantly less stress in 11 measures and were not different once; Wilt-Pruf was beneficial 10 times and not different twice; Folicote was beneficial nine times and not different three times; Vapor Gard produced eight beneficial results and four similar results; and Envy was beneficial three times and no different nine times. Species differences in response to antitranspirants as well as differences in product efficacy were demonstrated. UC86177 antitranspirant was shown to be as or more effective in controlling water status than the film-forming antitranspirants and may have potential for protecting various plant species against water stress.
Four topics are presented on the status of water in seeds; 1) methods to express moisture content (MC), 2) methods to determine MC, 3) relationship between relative humidity (RH) and MC, and 4) utility of water activity measurements in seeds. Seed MC is expressed on a fresh-weight basis in commerce and seed technology, while dry weight basis is used in physiological or biophysical literature. Conversion equations are available for the fresh and dry weight measurements. Moisture testing methods are grouped as primary and secondary. Primary methods are direct methods in which the water is removed and determined, while the secondary methods are indirect methods that rely on a chemical or physical characteristic that changes with MC. The oven method is the most common primary technique and the electronic moisture meter is widely used as a nondestructive secondary technique. The relation between RH and MC is known as an isotherm, and three zones of water binding are observed. The RH and the seed composition, in particular the lipid content, determines the MC. Seeds with low lipid content have a greater equilibrium MC than seeds with high lipid content. Water activity, defined as the ratio of water vapor of the seed over the water vapor of pure water at a particular temperature, is related to water potential in a log-linear relationship. Water activity (aw) can be used to define the water status of any species, regardless of composition.
Gas exchange and growth of transplanted and nontransplanted, field-grown Norway maple (Acer platanoides L. `Schwedleri') and littleleaf linden (Tilia cordata Mill. `Greenspire') trees were investigated in an arid climate. In the spring of 1995, three trees of each species were moved with a tree spade to a new location within a field nursery and three nontransplanted trees were selected as controls. Predawn leaf water potential, morning-to-evening stomatal conductance and leaf temperature, leaf-to-air vapor pressure difference, midday stomatal conductance and photosynthetic rate, and growth data were collected over a 2-year period. After transplanting, weekly predawn leaf water potential indicated that transplanted trees were under greater water stress than were nontransplanted (control) trees. However, predawn leaf water potential of maple trees recovered to control levels 18 weeks after transplanting, while that of transplanted linden trees remained more negative than that of controls. In 1995, stomatal conductance and photosynthetic rates were lower throughout the day for transplanted trees. In 1996, gas exchange rates of transplanted maple trees recovered to near control levels while rates for transplanted linden trees did not. Sensitivity of stomata to leaf-to-air vapor pressure difference varied with species and with transplant treatment. Each year transplanted trees of both species had less apical growth than did control trees. Although gas exchange and apical growth of transplanted trees was reduced following transplanting, recovery of gas exchange to control rates differed with species.
Some plant-derived natural volatile compounds exhibit antifungal properties and may offer a tremendous opportunity to control the causes of postharvest spoilage without affecting fresh produce quality or leaving a residue on the produce. E-2-hexenal has shown significant potential for use as a fumigant for controlling Botrytis cinerea in prior studies. In in vitro studies on the mode of action of E-2-hexenal, mycelial growth and percent spore germination were inversely proportional to concentrations of the compound. Spore germination was found to be more susceptible to the compound then mycelial growth. Much higher concentrations of E-2-hexenal were required to inhibit mycelial growth than spore germination. Lower concentrations of the compound significantly stimulated mycelial growth, especially when the volatile was added 2 days following inoculation. Light microscopy analysis revealed that a high concentration of the volatile damaged fungal cell wall and membranes. Treatment with a high vapor phase level of E-2-hexenal during postharvest storage of strawberry fruit at 2°C prevented botrytis development in a subsequent storage period at 15°C. However, treatment with a low vapor phase level enhanced botrytis development. The implications of these results with respect to the practical use of E-2-hexenal and other natural volatile compounds will be discussed.
Abstract
Differences in the photosynthetic capacity of leaves of peach [Prunus persica (L.) Batsch cv. Golden Glory] were investigated in conjunction with their leaf nitrogen and phosphorus content. Photosynthetic CO2 assimilation expressed on a leaf area basis, mesophyll conductance, and leaf conductance to water vapor were all linearly related to leaf nitrogen content expressed on a leaf area basis (R2 = 0.908, 0.921, 0.685, respectively). Leaf intercellular CO2 concentrations tended to decrease slightly with increasing CO2 assimilation rates and leaf N contents, indicating that CO2 assimilation was not being restricted by low intercellular CO2 concentrations and leaf conductances in leaves with lower assimilation capacity. CO2 assimilation, mesophyll conductance, and leaf conductance to water vapor were also linearly related to leaf phosphorus content, but these relationships were not as clear as for leaf nitrogen content. (R2 = 0.601, 0.687, 0.324, respectively). The maximum CO2 assimilation rate per unit of leaf nitrogen for peach leaves in this experiment was between 6.0 and 7.0 nmol CO2 mg N−1 s−1.
Abstract
Mature bearing pear [Pyrus communis L. ‘Beurre d’Anjou’ (‘Anjou’)] trees in an arid climate were irrigated weekly at 125% of pan evaporation (wet), biweekly at 100% of pan evaporation (normal), or irrigated only twice (dry) during the summer (1980, 1981), and were fertilized with and without 0.9 kg of supplemental N. Prior to final fruit harvest in 1981, depletion of available soil moisture (ASM) averaged 10%, 16.7%, and 89% for the wet, normal, and dry treatments, respectively. Mid-day leaf water potential (ψL) was correlated with the level of ASM only on bright days of high vapor pressure deficit. Stomatal conductance (κs) and transpirational flux density (F) of dry treatment leaves was lower than that of either wet or normal treatment leaves ψL exceeded −1.4 to −1.7 MPa. Resistance to vapor (water) transport (Rν) of fruit was independent of irrigation regime. Terminal buds had set on shoots from all 3 irrigation regimes at 58 days after full bloom (AFB) in 1981, but resumed growth on normal and wet treatment shoots at 87 days AFB. On 7 of 10 sampling dates during 1981, dry treatment fruit weighed less than normal or wet treatment fruit.
Abbreviations: A, net photosynthesis; CYV, canopy volume; E, transpiration; FCYV, fraction of canopy volume; GCA, general combining ability; g 1 , leaf conductance of water; LT, leaf temperature; SCA, specific combining ability; VPD, vapor pressure
Broccoli tissue, ranging in weight from 7 to 21 g, was sealed in packages made from low-density polyethylene (LDPE) of various thickness and permeability to establish a range of O2 levels in the package headspace. A pouch containing either hydrogen peroxide (H2O2) or water as a control was also sealed in the package. For packages that developed anaerobic atmospheres, inclusion of H2O2 permitted the maintenance of aerobic conditions for up to 3 days at ambient room temperature. These results suggest that the plant tissue is able to actively metabolize the H2O2 vapor to generate O2, which will prevent the development of low-O2 conditions in packaged produce, even under conditions of elevated storage temperature.
A water flow model was developed which uses irradiance, leaf-to-air vapor concentration difference, and soil water potential to establish stomatal conductance. Water flow to the roots was computed using a linear approximation of radial flow through the soil toward the axis of the roots across concentric shells. Root length density and soil rooting volume within four separate layers or compartments were included in the model. The simulation was executed in small time step iterations. A small increment of transpiration was translated to a water content deficit at the root and then sequentially through the concentric shells to simulate water uptake and change of soil water potential. The change in soil water potential was used to increment changes in stomatal conductance and transpiration. The output of the model simulated the pattern of diurnal stomatal behavior observed in other types of experiments, as well as the total soil water extraction patterns of young potted citrus trees.
Postharvest treatments significantly reduced or eradicated pests on various tropical cut flowers and foliage. Immersion in water at 49° C for 10 minutes killed armored scales on bird of paradise leaves, Strelitzia reginae Banks, as well as aphids and mealybugs on red ginger, Alpinia purpurata (Vieill.) K. Schum. Vapor heat treatment for 2 hours at 45.2° C provided quarantine security against armored scales on bird of paradise leaves. A 5 minute dip in fluvalinate combined with insecticidal soap eliminated aphids and significantly reduced mealybugs on red ginger. A 3 minute dip in fluvalinate, a 3 minute dip in chlorpyrifos, or a 3 hour fog with avermectin-B significantly reduced thrips on orchids, Dendrobium spp., without injury to the flowers. No postharvest treatment was both effective and nonphytotoxic on all commodities.