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It has been previously reported that sub-lethal heat treatments of cold hardy Azalea (45C) and grape floral buds (47-50C) for 2 hours altered deep supercooling by shifting low temperature exotherms (LTE) to warmer temperatures. Heat treatments were shown to modify suberized tissues in Azalea which may function as an ice barrier required for deep supercooling. Our study examined deep supercooling of Loring peach buds subjected to heat treatments ranging from 40 - 49C. Temperatures above 43C for 2 hours resulted in visible injury to floral tissues. However, 65% of these buds continued to exhibit deep supercooling. Tissue injury was not observed at 40C, however longer exposure durations (16-24h) were required to shift LTEs to warmer temperatures. Moderately hardy buds (avg LTE -15C) were responsive to 40C treatment whereas, extremely hardy buds (avg LTE -20C) were not. Pre-disposing extremely hardy buds to deacclimating conditions by placing twigs in water in the greenhouse for 24h, elicited a response to heat treatment and promoted warm temperature shifts of the LTE. It appears that tissue-water status of floral buds may play a role in their response to sub-lethal heat treatment.

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Gamete selection was examined as a breeding tool in developing Phalaenopsis hybrids that are more cool or warm temperature tolerant. Four pairs of hybrid cultivars of Phalaenopsis were cross-pollinated, and then exposed to two temperature extremes, 30 °C / 25 °C and 14 °C/9 °C, during pollen tube development and subsequent fertilization. One of each pollinated orchid cultivar was placed in either of two growth chambers and exposed to an 11-h photoperiod with an irradiance of 180 μmol·m-2·s-1 and a relative humidity of 70% during the day and 50% at night for 3-7 days depending on the temperature treatment. The plants were returned to the greenhouse after the initiation of fruit set and the pods were collected after 150 days. Seeds collected from these treatments were surface-sterilized, placed on Phytamax medium and evaluated for protocorm development after 73 days on a thermogradient table ranging from 10 to 30 °C. For the first family for which reciprocal crosses were available, the number of protocorms per plate ranged from 0 in the coldest treatments to 290 at 28 °C. For cold pollinated seeds, protocorm development was optimum at 22 and 28 °C (means of 290 and 250 protocorms per plate, respectively) whereas the greatest protocorm development for warm pollinated seeds occurred at 20 °C (103 protocorms per plate). Of the 1471 total protocorms scored, 1095 were from cold pollinations, whereas 376 were from the warm pollinations. Additional replication is required to confirm the greater germinability of cold-pollinated seed at higher temperatures.

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Black polyethylene mulch is preferred for producing early spring tomatoes (Lycopersicon esculentum Mill.) because of its warming effect on the soil around the roots. However, using the same mulch for double-cropping cucumbers (Cucumis sativus L.) with tomatoes is considered by some growers to be undesirable because of the belief that heat accumulation under the mulch in midsummer or early fall is detrimental to cucumber yield. Eight studies were conducted from July to September in 1994, 1995, and 1996 to determine the effects of mulching spring tomatoes with black vs. white polyethylene mulch on the growth and yield of subsequent cucumber crops. Soil temperature recorded after planting cucumbers ≈4:00 pm for 3 weeks was higher under black mulch than under white mulch. Color of the mulch did not affect leaf length, leaf width, and plant dry weight of cucumbers in six of the eight studies. Cucumbers grown on black mulch produced longer leaves in one study and wider leaves in two studies, and plant dry weight was lower in two studies. Mulch color had no significant effect on the premium or total yields of cucumbers in all but one study. Cucumbers grown on black mulch produced lower percentages of culls in two studies.

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Ethylene production in stem tissues of red-osier dogwood (Cornus sericea L.) following heat treatment was determined at several growth stages. Ethylene production of heat-stressed stem tissue depended on the stage of development and was a function of the degree of stress. During active growth and early endodormancy, heat stress of stem tissues stimulated ethylene production, reaching a peak at 40C, followed by a steady decrease at higher temperatures. Highest ethylene levels from stressed tissues occurred in May, July, September, and March. Only a trace amount of ethylene was produced during endodormancy to ecodormancy (late October to January) from stressed and nonstressed stem tissues. Applying ACC to stem segments at late endodormancy (December) or applying methionine and IAA to stem segments at maximum endodormancy (November) enhanced ethylene production of both nonstressed and heat-stressed stem tissues. Chemical names used: 1 H- indole-3-acetic acid (IAA); 1-aminocyclopropane-1-carboxylic acid (ACC).

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Mature-green tomato (Lycopersicon esculentum Mill.) fruit, when kept for 3 days at 36, 38, or 40C before being kept at 2C for 3 weeks, did not develop chilling injury, while unheated fruit placed at 2C immediately after harvest did. When removed from 2 to 20C, the heated tomatoes had lower levels of K+ leakage and a higher phospholipid content than unheated fruit. Sterol levels were similar in heated and unheated fruit while malonaldehyde concentration was higher in heated fruit at transfer to 20C. The unheated tomatoes remained green, and brown areas developed under the peel; their rate of CO2 evolution was high and decreased sharply, while ethylene evolution was low and increased at 20C. In contrast, the heat-treated tomatoes ripened normally although more slowly than freshly harvested tomatoes: color developed normally, chlorophyll disappeared, and lycopene content increased, CO2, and ethylene evolution increased to a climacteric peak and K+ leakage increased with time. During prestorage heating, heat-stress ethylene production was inhibited, protein synthesis was depressed, and heat-shock proteins accumulated. There appears to be a relationship between the “heat shock response” and the protection of tomato fruit from low-temperature injury.

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In an effort to increase lima bean yields in Delaware, the documentation of lima bean plant development and the comparison of Delaware and California lima bean production was conducted. Delaware lima bean yields have averaged 1905 kg·ha-1 for the last 30 years. California averages 3923-4484 kg·ha-1. Cultivar M-15 is used by both states for production. Plant population density, plant fresh weight, and final yield was greater in California than in Delaware. Although plant populations were the same in 1992, yields remained higher in California than in Delaware. High night temperatures have an adverse affect on lima bean yields. Minimum temperatures from both states were compared. Minimum temperatures from the California planting were greater than the minimum temperatures for the late planting in Delaware.

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Electrolyte leakage was used to quantify heat stress injury in `Early Calwonder' pepper (Capsicum annuum L.) leaf disks. Lethal temperatures were estimated from the midpoint of the sigmoidal response curve. An interaction between exposure temperature and duration was observed, with lethal temperatures decreasing linearly from 53 to 46C as exposure duration increased exponentially from 5 to 240 min. Exposure to two 7.5-min periods at 51.5C, interrupted by 4 hours at 21C, resulted in the same injury as a continuous 15-min exposure to 51.5C. Plants grown at 22/20C day/night cycles and held 24 hours at 38/30C had increased their heat tolerance by 3C, 51 to 54C; these plants reacclimated to 52C 48 hours after having been transferred back to 22/20C. Leaf disks acclimated significantly in vitro in 1 hour and were fully acclimated by 4 hours at 38C.

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Particle film technology is a developing pest control system for tree fruit production systems. Trials were performed in Santiago, Chile, and York Springs, Pa., Wenatchee and Yakima, Wash., and Kearneysville, W. Va., to evaluate the effect of particle treatments on apple [Malus sylvestris (L.) Mill. var. domestica (Borkh) Manst.] leaf physiology, fruit yield, and fruit quality. Leaf carbon assimilation was increased and canopy temperatures were reduced by particle treatments in seven of the eight trials. Yield and/or fruit weight was increased by the particle treatments in seven of the eight trials. In Santiago and Kearneysville, a* values of the fruit surface were more positive in all trials although a* values were not increased in Wenatchee and Yakima. Results indicate that particle film technology is an effective tool in reducing heat stress in apple trees that may result in increased yield potential and quality.

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, suggesting that heat stress was the cause of growth reduction in bell pepper plants. Similarly, in tomato and tomatillo grown in Tifton, GA, like in this study, the use of dark mulches produced high RZTs resulting in reduced plant vegetative growth during the

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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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