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Sanalkumar Krishnan, Yingmei Ma, and Emily Merewitz

wounding stress other than mowing. In addition, how the major hormones described in this paper respond to heat stress in turfgrass species is not well documented. Therefore, the objectives of the study were to evaluate hormone profiles in response to

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M.M. Peet, C. Clement, and S. Sato

Starting 2 weeks before anthesis of the first flower, tomato cultivars (Lycopersicon esculentum Mill.) differing in heat tolerance were exposed to mild heat stress (31/24 vs. 28/22 °C) at three levels of relative humidity (30%, 60%, and 90%) in controlled environment chambers at the Duke Univ. Phytotron. Pollen development in the anthers was followed cytologically, pollen release was measured at anthesis, and seed production and fruit weight were measured as fruit matured. Fruit and seed development were best at 60%RH and 28/22 °C and worst at 90% RH and 31/24. Seed development was poor at 31/24 °C at all humidity levels. It was also poor at 28/22 in the 90% RH treatment. Low relative humidity had a greater negtive effect on fruit and seed production and on cytological development in plants grown at high temperature. Pollen release was also reduced at 90% RH, with virtually no pollen released at 31/24 °C. Cytological examinations revealed developmental anomolies in pollen in some, but not all cultivars at 90% and 30% RH. Plant height was also affected by the treatments, with much taller plants in the high-temperature, high-humidity treatments.

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Stephen S. Deschamps and Shinsuke Agehara

in March. To speed up establishment and increase early yields, Florida strawberry growers have recently begun to advance transplanting dates from mid October to late September. As a result, plants are exposed to even greater heat stress conditions

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Yan Xu and Bingru Huang

transport. Cool-season turfgrass species such as Agrostis stolonifera are sensitive to heat stress and experience a series of physiological injuries when exposed to temperatures above 30 °C. Leaf senescence was observed after 20 d at 30 °C and only 8 d at

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Wenjie Ma, Wen Liang, and Bing Zhao

As plants are sessile organisms that cannot avoid heat, they often encounter harsh heat stress ( Wang et al., 2018 ). Heat stress can impose different metabolic and physical challenges on almost all aspects of plant development, growth, reproduction

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Renée L. Eriksen, Laban K. Rutto, James E. Dombrowski, and John A. Henning

node below the youngest, fully unfurled leaf because young and mature senescing tissues have different sensitivities to heat stress ( Karim et al., 1999 ; Marias et al., 2017 ). Dark-adapted F o and F V /F M measurements were performed after 10 h of

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Sylvie Jenni, David de Koeyer, and George Emery

(20.2 °C and 125 mm rainfall in 2001 and 20.7 °C and 123 mm rainfall in 2002), the lettuce heads harvested within 50 and 51 d experienced 15 d (2001) and 19 d (2002) of heat stress above 28 °C. In the first planting of 2001, the susceptible parent had

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Dennis A. Schaff, Carl D. Clayberg, and George A. Milliken

Abstract

Two laboratory techniques for estimating genotypic differences in response to heat stress—the electrical conductivity and the 2,3,5-triphenyl tetrazolium chloride reduction tests—were compared in tests with 26 cultivars of beans (Phaseolus vulgaris L.) previously evaluated for heat tolerance. After heat acclimation of plants, leaf disks were subjected to heat stress over a range of temperatures. The temperature causing 50% injury above the control, considered as the killing temperature, was estimated by fitting the data to a sigmoidal model. Although cultivar killing temperatures were correlated between tests, only killing temperatures for the conductivity test were correlated with yield performance under stress in the field.

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Katsumi Suzuki, Tadashi Tsukaguchi, Hiroyuki Takeda, and Yoshinobu Egawa

Pod yield of `Kentucky Wonder' green bean (Phaseolus vulgaris L.) decreased at high temperatures due to a reduction of pod set. A highly positive correlation was observed between pod set and pollen stainability in flowers that were affected by heat stress about 10 days before anthesis. Pollen stainability was decreased by heat stress applied 8 to 11 days before flowering under controlled environment conditions. When mean air temperature during this period exceeded 28 °C, pollen stainability decreased under field conditions. Low pollen stainability indicated sensitivity to high temperatures about 10 days before flowering. A heat-tolerant cultivar showed higher pollen stainability than did heat-sensitive cultivars under high temperatures. These results demonstrated that heat tolerance at an early reproductive stage could be evaluated by analyzing pollen stainability using flowers developed under high temperatures.

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Ritu Dhir, Richard L. Harkess, and Guihong Bi

Ivy geranium ( Pelargonium peltatum L.) is an important floriculture crop but it does not tolerate the high temperatures of southeastern U.S. summers. Under heat stress, the newly developing leaves of ivy geranium are partially or completely white