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R.G. Linderman and E.A. Davis

primary objective was to determine the effectiveness of heat treatment via aerated steam mixtures, and fumigation with metam sodium, in eradicating P. ramorum (the European A1 and North American A2 mating types) and other soilborne pathogens including

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Michael Wisniewski, Jörg Sauter, Valerie Stepien, and Les Fuchigami

Sublethal heat stress has been shown to decrease or eliminate deep supercooling of flower buds in woody plants and to release plants from endodormancy. Experiments were conducted to characterize the effect of heat stress on endodormancy and ecodormancy in peach (cv Loring) and two hybrid poplars. Protein synthesis (de novo) and patterns of protein expression were also monitored. In order to determine optimum treatment temperatures, shoots, collected September-March, were exposed to a range of temperatures (35-60 C) under wet or dry conditions for 1-6 h. Shoots were then placed in the greenhouse and cumulative budbreak was monitored over 4 weeks. Samples of bud and bark tissues were collected during and up to 72 h after heat treatment for SDS-PAGE analysis. Data indicate: 1) twigs must be immersed in water for the heat treatments to be effective; 2) heat treatments resulted in a release from endodormancy and a decrease in thermal units needed for budbreak during ecodormancy; 3) 40 C for 2-4 h was optimum in fall and late winter whereas 45 C was the optimum temperature to induce budbreak in midwinter; 4) optimum temperature for peach floral buds (37.5 C/2h) was lower than for vegetative buds (40 C/4h), and 5) heat treatments also decreased cold hardiness. Protein synthesis decreased significantly following heat treatment but was significantly greater than controls (room temp) 24-48 h after heat treatment.

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Rosa E. Raudales, Tracy A. Irani, Charles R. Hall, and Paul R. Fisher

ionization, copper sulfate, filtration (excluding membrane filtration), heat treatment and pasteurization, hydrogen peroxide, hypochlorous acid, ozone, reverse osmosis/membrane filtration, silver ionization, sodium hypochlorite, and ultraviolet radiation

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Krista C. Shellie

Export and domestic marketing of grapefruit (Citrus paradisi Macf.) can be limited by phytosanitary barriers against fruit fly species and growth of decay organisms, especially green mold (Penicillium digitatum Sacc.), during the marketing process. The objective of this research was to identify whether the dose of high-temperature forced air that providing quarantine security against Mexican fruit fly could also beneficially control the growth of green mold during subsequent storage. `Rio Red' grapefruit were harvested four times in 1995 and nine times in 1996 and challenge-inoculated with 10 L of a 1 × 106 spores/ml spore solution (10,000 spores) of green mold before or after exposure to 46°C forced air for 300 min. Control fruit were challenge-inoculated but not exposed to the heat treatment. The growth of green mold was quantified by measuring lesion diameter after 3 days of storage at 23°C, 80% RH. Grapefruit inoculated prior to the heat treatment developed significantly smaller lesions than fruit inoculated after the heat treatment or fruit not exposed to a heat treatment. The average lesion diameter of fruit inoculated prior to the heat treatment was 2.5 and 0.9 cm, respectively, in 1995 and 1996. The average lesion diameter of fruit inoculated after the heat treatment was similar to non heat-treated, control fruit. Lesion diameter of control and post heat-challenged fruit were 6.4 and 6.1 cm in 1995 and 5.7 and 5.3 cm in 1996. Results suggest reduction in decay be attributed to alteration in the pathogenicity of green mold after exposure to the heat treatment rather than an altered resistance of the fruit to the pathogen.

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Jun Song, Lihua Fan, Charles F. Forney, and Michael A. Jordan

Volatile emissions and chlorophyll fluorescence were investigated as potential signals of heat injury for apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] fruit. `McIntosh', `Cortland', `Jonagold', and `Northern Spy' apples were exposed to 46 °C for 0, 4, 8, or 12 hours (heat treatments). Following treatments, fruit were kept at 20 °C and evaluated after 1, 2, 4, or 7 days. Heat treatments induced volatile production including ethanol and ethyl acetate. The 8 and 12 hours heat treatments increased ethanol and ethyl acetate production in all four cultivars by as much as 170- and 11-fold, respectively, 1 day after treatments. Heat treatments also reduced ethylene production and chlorophyll fluorescence. Heat for 12 hours caused serious flesh browning. Among the cultivars investigated, `Northern Spy' and `McIntosh' were most susceptible to heat stress based on the degree of flesh browning. Correlation coefficients of heat stress induced ethanol emission and chlorophyll fluorescence with flesh browning were 0.82 and -0.66, respectively. The nondestructive measurements of ethanol emission and chlorophyll fluorescence have potential to identify stressed fruit with reduced quality or compromised storage life.

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Lihua Fan, Jun Song, Charles F. Forney, and Michael A. Jordan

Ethanol concentration and chlorophyll fluorescence (CF) were measured as signs of heat stress in apple fruit [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.]. `McIntosh', `Cortland', `Jonagold', and `Northern Spy' apples were placed in trays and exposed to 46 °C for 0, 4, 8, or 12 hours. Following treatments, fruit were stored in air at 0 °C and evaluated after 0, 1, 2, or 3 months. Ethanol and ethylene production, CF, peel and flesh browning, firmness, skin color, soluble solids, and titratable acidity were measured. Increases in ethanol were apparent immediately following 12-hour heat treatments as well as after 3 months. After 3 months, ethanol concentrations were 16-, 52-, 6-, and 60-fold higher in `McIntosh', `Cortland', `Jonagold', and `Northern Spy' apples than in controls, respectively. The concentrations of ethanol accumulated reflected the degree of heat-induced fruit injury. Heat treatments reduced ethylene production relative to control values. After 3 months of storage ethylene production of fruit exposed to 46 °C for 12 h was <0.48 μmol·kg-1·h-1 compared to >4.3 μmol·kg-1·h-1 for controls. Heat treatments also reduced CF which was expressed as Fv/Fm, where Fv is the difference between the maximal and the minimal fluorescence (Fm - Fo), and Fm is the maximal fluorescence. After 3 months storage at 0 °C, Fv/Fm was ≈0.2 in fruit held at 46 °C for 12 hours compared with 0.5-0.6 for control fruit. Exposure to 46 °C for 12 hours caused severe peel and flesh browning in all cultivars. Severity of peel and flesh browning increased with increasing duration of heat treatment and subsequent storage at 0 °C. `Northern Spy' apple fruit were most susceptible to heat stress based on the degree of flesh browning. Heat treatments of 8 and 12 hours reduced firmness of `McIntosh', `Cortland', and `Northern Spy', but not `Jonagold' apples. Hue angle of the green side of fruit was also reduced in `Cortland', Jonagold' and `Northern Spy' apples receiving the 8- and 12-hour treatments. Heat treatments caused a decrease in fruit tiratable acidity, but had no effect on soluble solids content. The increase in ethanol production and decrease in CF correlated with heat-induced injury, and were apparent before browning was visually apparent. Ethanol and CF have the potential to be used to nondestructively predict the severity of injury that develops during storage.

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Shiow Y. Wang and Miklos Faust

The ability of low and high temperatures to overcome endo- and paradormancy along with the possible mechanisms involved in these treatments for breaking apple (Malus domestica Borkh. `Anna') bud dormancy were studied. All these treatments induced budbreak in paradormant (in July) and endodormant (in October) buds. Cold and heat treatments increased ascorbic acid, the reduced the form of glutathione (GSH), total glutathione, total non-protein thiol and non-glutathione thiol, whereas dehydroascorbic acid and oxidized glutathione (GSSG) decreased. The treatments also increased the ascorbic acid: dehydroascorbate and GSH: GSSG ratios and the activity of ascorbate-free radical reductase, ascorbate peroxidase, dehydroascorbate reductase, ascorbate oxidase, and glutathione reductase in the buds. These results indicate that budbreak induced by cold and heat treatments is associated with the removal of free radicals through activated peroxide-scavenging systems.

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Abbas M. Shirazi, Leslie H. Fuchigami, and Tony H.H. Chen

Red-osier dogwood sterns, Cornus sericea L., at ten different growth stages were subjected to a series of temperatures ranging from 25C to 60C by immersing them in a water bath for one hour. After heat treatments, the viability of internode tissues were determined by electrical conductivity and ethylene production. Heat tolerance was expressed as LT50, the temperature at which 50% of the tissues were injured. The results suggest that the LT50 of dormant plants remained relatively constant, approximately 53C. During dormancy, heat stress did not stimulate ethylene production from internode tissues. In contrast, tissues from non-dormant plants exposed to heat stress produced increasing levels of ethylene reaching a peak at 40C followed by a steady decrease at higher temperatures. Application of 1-aminocyclopropane-1-carboxylic acid (ACC) to stem segments from dormant plants, following heat treatment, enhanced production of ethylene.

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Gagnon André Yelle Serge

In the summer of 1992, a 4-year research program on the utilisation of propane in agriculture was initiated between ICG Propane and Lava1 University. Experiments were conducted to evaluate the effects of propane burners on weed control as a pre-establishment treatment. The data indicate that the efficiency of weed control is related to tractor speed and gas pressure. When weed height is between 1 and 2 centimetres, most of the heat treatments were as effective as those with the herbicide paraquat. The best and most economical heat treatment was at a tractor speed of 6 Km-hr and a gas pressure of 65 PSI. With larger weeds, efficiency increased with reduces tractor speed and increased gas pressure. In addition, high intensity treatments provided excellent control on broadleaf weeds but were less efficient on grass species. A preliminary economical evaluation showed that propane burners are competitive with chemical herbicides and large-scale commercial trials are planned for summer 1994.

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James D. Hansen, Arnold H. Hara, and Victoria L. Tenbrink

Vapor heat treatments to disinfest tropical cut flowers and foliage were evaluated using a commercial facility. Efficacy was determined for specific durations against representative Hawaiian quarantine pests on their plant hosts. Nymphs and adults of aphids, soft and armored scales, mealybugs, and thrips were killed after 1 hour at 46.6C, and both life stages of aphids and armored scales along with mealybug nymphs after 2 hours at 45.2C. Injury to several varieties of Hawaiian floral commodities (Araceae, Musaceae, Zingiberaceae, Heliconiaceae, Orchidaceae, Marantaceae, Lycopodiaceae, Agavaceae, Proteaceae) during these treatments was determined. Large heliconias, most red ginger, bird-of-paradise flowers and leaves, and most foliage were not damaged; anthuriums, pincushion protea, and orchid flowers and foliage were very sensitive to vapor heat. Treatment modification was needed to reduce plant injury to these commodities without losing efficacy. The number of shelf-life days of the treated plant material was estimated from the visual ratings.