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I. David van der Walt and Gail M. Littlejohn

The influence of storage temperature and humidity on pollen viability was studied in four Protea species. Pollen was stored at a range of temperatures and relative humidities for up to 1 year and tested for ability to germinate in vitro. Pollen of P. repens (L.) L. `Sneyd', P. eximia (Salisb. ex Knight) Fourcade `Fiery Duchess' and P. magnifica Link. clone T 84 07 05 stored at -196 °C and -14 to -18 °C retained a germination percentage as high as that of fresh pollen regardless of humidity. Humidity control became increasingly important at storage temperatures above 0 °C. The study showed that long-term storage of Protea pollen is not feasible at temperatures above 0 °C. The relationship between germinability and fluorochromasia (FCR) was studied during storage of `Sneyd' pollen. The correlations between FCR and germinability were found to be low and nonsignificant. Fifteen-month-old cryopreserved `Sneyd' pollen functioned in fertilization and seed set as effectively as fresh pollen.

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Albert F. Elboudwarej and Robert C. Herner

In 1987, 1988, and 1989, the behavior of four different table grape varieties including Alden, Concord, Himrod, and Vanessa were studied during storage at 0°C.

The first objective of our study was to determine the behavior of table grapes in modified atmosphere packages in terms of general acceptance. After three years of experimenting with these three films we were able to obtain a modified atmosphere of about 3% O2 and 10-15% CO2 at 0°C using a 3 mil thickness LDPE.

Our second objective was to use moisture absorbents as a means of reducing the relative humidity inside the void volume of a package by the inclusion of different desiccants in the package to establish a desirable relative humidity.

Examining different storage characteristics, our data showed that `Himrod', `Vanessa', and `Concord' grape clusters stored in the presence of KNO3 and KCl had better quality compared to grape clusters stored in the presence of other sorption compounds or controls with no sorbants.

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Phil S. Allen, Donald B. White, Karl Russer, and Dave Olson

An inexpensive system for maintaining desired water potentials throughout seed germination was developed. During hydration, a water reservoir at the base of inclined petri dishes allowed continual saturation of filter paper on which seeds were placed. During dehydration, seeds were exposed to equilibrium vapor pressures above saturated salt solutions. Constant temperature, necessary to prevent condensation of water vapor, was achieved via a small (0.2 A) fan that furnished and circulated heat throughout an insulated chamber in which salt solutions were placed. By operating the chamber above ambient laboratory temperature, interior cooling was not required. The system allowed manipulation of the rate, degree, and frequency of dehydration episodes to which germinating seeds were exposed.

Open access

E. Chalutz and G Felsenstein


We discuss criteria for the design of cold storage facilities for use in research. Factors considered are: determination of the desired accuracy of temperature and relative humidity control, methods of air circulation and fresh air introduction.

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D. Clay Collins and Steven E. Newman

The Leaf Wetness Data Logger (LWL) and accompanying Logbook software were designed by Spectrum Technologies Inc. as a low-maintenance tool to aid in disease prediction and spray scheduling for outdoor field-grown crops. The LWL mimics leaf surface moisture represented as a value between 0 (dry) and 15 (wet). We explored an expanded use of the LWL to large-scale commercial greenhouses for the purpose of humidity control and disease prevention. Data were collected over 15 days in a commercial hydroponic tomato production greenhouse and repeated. Results indicated that leaf wetness, as determined by the LWL, increased during irrigation periods, with cumulative effects dependent on daily irrigation requirements and climate. Irrigation was controlled by the climate control computer in response to cumulative radiation intensity. By analyzing leaf wetness in correlation with climatic conditions, more adequate irrigation scheduling may be implemented, reducing the risk of disease spread and infection.

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Ahmad Shirazi and Arthur C. Cameron

The feasibility of controlling relative humidity in modified atmosphere packages using compounds possessing Type III sorption isotherm behavior was studied. Ten grams each of dry sorbitol, xylitol, NaCl, KCl, or CaCl2 sealed with one maturegreen tomato (Lycopersicon esculentum L.) fruit at 20C in simulated packages for 48 days resulted in stable relative humidities of ≈75%, 80%, 75%, 85%, and 35%, respectively. Relative humidity was a function of the ratio of chemical to fruit mass. Relative humidities within control packages were in the range of 96% to 100% throughout the experiments. A simple system that uses spunbonded polyethylene pouches for the application of this humidity control method to packages is described. The storage life of packaged red-ripe tomato fruit at 20C was extended from 5 days using no pouch to 15 to 17 days with a pouch containing NaCl, mainly by retardation of surface mold development.

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Anthony V. LeBude, Frank A. Blazich, and Barry Goldfarb

Experiments conducted in January (hardwood cuttings) and June (softwood cuttings) 1998 compared rooting and root dry weight (DW) of stem cuttings of three full-sib families of loblolly pine (Pinus taeda L.) rooted in Jiffy forestry peat pellets and Ray Leach Super Cells. Ray Leach Super Cells (vol.= 162 cm3) served as the control and contained a medium of 2 peat: 3 perlite (v/v). Pellet sizes used were 25-65, 30-65, 36-65, 36-75, 42-65, 42-80, and 50-95 (dry diam.-expanded height in mm). Cuttings were taken from hedged stock plants and rooted for 12 weeks under mist in a humidity-controlled greenhouse. Following evaluation for rooting in the June experiment, ≈500 rooted cuttings in pellets and Ray Leach Super Cells were field-planted in eastern Georgia in December 1998 to study the effect of pellet size and cutting development on first-year field growth. Rooting percentages in January for hardwood cuttings rooted in pellet sizes 42-80 (36%) and 50-95 (57%) were less than the control (83%). Root DW for each pellet size was less than the control. Rooting percentage in June for softwood cuttings rooted in pellet size 36-65 (77%) was greater than the control (64%) whereas rooting percentages for cuttings rooted in pellet sizes 42-80 (50%) and 50-95 (52%) were less than the control. Root DWs for cuttings in pellet sizes 25-65, 30-65, 36-65, and 42-65 were less than the control. Field performance data will be presented.

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Kenneth A. Corey, Phil A. Fowler, and Raymond M. Wheeler

Reduced atmospheric pressures may be used to minimize mass and engineering requirements for plant growth habitats used in some extraterrestrial applications. A chamber with high vacuum capability and thermal control at Kennedy Space Center was used to measure water loss of lettuce plants at reduced atmospheric pressures. A test stand with three, high-pressure sodium vapor lamps was used to determine short-term plant responses to reduced pressure. Initial experiments with lettuce showed that a pressure of 10 kPa (≈0.1 atm) resulted in a 6.1-fold increase in the rate of water loss compared to water loss at ambient pressure. However, due to low relative humidity, plants wilted after 30 minutes exposure to 10 kPa. A follow-up experiment in which relative humidity was controlled between 70% and 85%, demonstrated that water loss was directly proportional to the vapor pressure gradient, regardless of atmospheric pressure in the pressure range of 10 to 101 kPa. However, the response was curvilinear, suggesting effects on the pathway resistance. Results indicate that plant growth at atmospheric pressures of 5 to 10 kPa should be achievable. Further work will necessitate better relative humidity control and carbon dioxide control in order to separate vapor pressure deficit effects from diffusion effects.

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J.L. Shipp and Yun Zhang

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.

Open access

Junhai Niu, Qingyun Leng, Guiyu Li, Shaohua Huang, Shisong Xu, and Xinge Lin

al., 1992 ). Anthuriums grow best when the maximum daytime temperatures range from 26 to 32 °C in advanced greenhouses equipped with temperature and humidity controls. However, in many tropical areas located far from their original habitat, they are