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Kemin Su, Dale J. Bremer, Richard Jeannotte, Ruth Welti and Celeste Yang

the present-day transition zone ( National Assessment Synthesis Team, 2000 ). Thus, understanding the mechanisms of heat tolerance is increasingly important for turfgrass breeders and managers. Cellular membranes, which are selectively permeable

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Sharon J. Keeler, John J. Frett and Sherry L. Kitto

Heat stress on field grown Phaseolus lunatus (lima bean) can have a significant influence on yield. Lima bean crops grown in Delaware typically yield less pounds per acre than the same cultivars grown in California. Part of this effect may be due to extreme heat conditions or fluctuations during Delaware's summers, which can affect blossom and pod set. Our purpose was to analyze the heat tolerance of various cultivars of P. lunatus using quick bioassays and to establish a relationship to yield in greenhouse temperature trials. Two assays were used. The first, a hypocotyl extension assay, consisted of a treatment of germinated seedlings at 25, 35, or 42 for 2 h and observations of hypocotyl extension at 72 and 96 h posttemperature treatments. Three cultivars [`Fordhook' 1072 (heat-sensitive), `Jackson Wonder' (heat-tolerant), and `Early Thorogreen' (heat tolerant)] were analyzed. Initial results indicated that `Jackson Wonder' and `Early Thorogreen' are capable of surviving the 42C heat shock, but `Fordhook 1072' is not. In the second assay, we measured electrical conductivity of a solution containing hypocotyl sections following incubation at various temperatures (R1). Tissue samples then were boiled and conductivity was measured again (R2). The ratios of R1/R2 × 100 were determined as percent injury. Preliminary data suggests that `Jackson Wonder' is more heat-tolerant in this assay than `Fordhook 1072'. Subsequent experiments will analyze the induction of specific heat shock proteins as a function of cultivar-specific heat tolerance.

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Feifei Li, Da Zhan, Lixin Xu, Liebao Han and Xunzhong Zhang

activities were associated with the differences in heat tolerance of turfgrasses and indicated a positive correlation between chlorophyll content and the antioxidant enzymes and a negative correlation between membrane injury index and the antioxidant enzymes

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Kuan-Hung Lin, Shao-Bo Huang, Chun-Wei Wu and Yu-Sen Chang

leaves ( Ecke et al., 2004 ). However, the effects of high temperatures on poinsettia morphology have not been adequately studied. Heat tolerance can be improved by genetic selection as well as by the use of exogenous regulators, which aid in the

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Magaji G. Usman, Mohd Y. Rafii, Mohd Razi Ismail, Mohammad Abdul Malek and Mohammad Abdul Latif

measuring electrolyte leakage from leaves of plants at different temperatures. Several studies have indicated that CMT is effective in detecting genetic differences with regard to heat tolerance among several crops ( Islam et al., 2014 ; Kumar et al., 2012

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Emily B. Merewitz and Sha Liu

Schmidt, 2000 ). Oxidative stress and differential antioxidant system activity were two key factors that contributed to differences among cultivars of creeping bentgrass in heat tolerance ( Liu and Huang, 2000 ). In addition to the antioxidant system, the

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Huifei Shen, Bing Zhao, Jingjing Xu, Xizi Zheng and Wenmei Huang

Rady, 2014a , 2014b ). Heat tolerance can be improved by genetic selection as well as with the use of exogenous regulators, which aid the adaptation of physiological response in plants. SA and Ca 2+ are recognized as signal molecules known for their

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D.W. Heather, J.B. Sieczka, M.H. Dickson and D.W. Wolfe

Forty hybrid broccoli [Brassica oleracea L. (Italica Group)] accessions were screened for heat tolerance and holding ability over three planting dates in 1988 at the Long Island Horticultural Research Laboratory in Riverhead, N.Y. Holding periods were quantified using the number of consecutive days between the time individual heads reached 10 cm diameter and cutting, which occurred when the sepals had fully expanded and had just begun to separate. In 1989 and 1991, heat stress was applied at various weeks during maturation to determine the most sensitive stage or stages of plant development in terms of reduction in holding period and head weight. Field studies and heat stress experiments indicate that heat stress may be most critical during the time the immature inflorescence measures 5 to 10 mm in diameter. This stage corresponds to ≈ 3 weeks before harvest for summer plantings in the northeastern United States.

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John M. Ruter

Temperatures producing heat damage in leaves of Ilex ×meserveae S.Y. Hu `Blue Prince' and Ilex rugosa × cornuta Lindl. & Paxt. `Mesdob' (China Boy) were evaluated using electrolyte leakage and chlorophyll fluorescence techniques. Whole leaves were exposed to temperatures from 30 to 65C for 30 minutes to determine critical midpoint heat-killing temperatures (TJ using electrolyte leakage techniques. The Tm for `Blue Prince' and `Mesdob' was 52.4 ± 0.lC and 53.8 ± 0.lC, respectively. Dark-adapted leaves were heated for 30 minutes in darkness at temperatures between 30 and 57C before chlorophyll fluorescence was measured. Initial (F0) and peak fluorescence measurements were higher at 54 and 55C for `Mesdob' than for `Blue Prince'. Cultivar had no effect on variable fluorescence (F,). Based on the Fv: Fo ratio, `Mesdob' was estimated to have a higher optimal plant growth temperature than `Blue Prince'. The physiologic data support the hypothesis that I. cornuta as a parent conferred heat tolerance to the interspecific hybrid in this study.

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Yan Xu and Bingru Huang

mechanisms of plant heat tolerance. Recently, a heat-tolerant C 3 perennial grass species, Agrostis scabra , has been identified growing in geothermally heated areas in Yellowstone National Park, Wyo. ( Stout and Al-Niemi, 2002 ). It survives or even