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Abstract

Injury to ‘Prelude’ and ‘Manhattan II’ perennial ryegrass (Lolium perenne L.) was measured as percentage of electrolyte leakage from leaf segments after stress to determine the influence of prestress growth temperature and poststress temperature on heat tolerance. The temperature required to cause 50% cell solute efflux was 59.5°C for ‘Prelude’ and 56.5° for ‘Manhattan II’, when measured immediately after stress treatment. However, electrolyte leakage increased with time after termination of stress. When measured 24 hr after termination of stress, 52° caused 50% cell solute efflux from leaf segments of both cultivars. Injury levels 44 hr after 30 min at 50° were ≈ 12% and 89% when incubated at poststress temperatures of 7° and 35°, respectively. Incubation temperature following a 55° treatment did not affect electrolyte leakage rate in either cultivar. Greater injury occurred in both cultivars when grown at 25° than at 41°.

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al., 2008 ). Heat tolerance is a complex trait that varies with the severity of stress and plant growth stage. Therefore, there is a need to identify heat-tolerant carrot germplasm with stable growth and yield under high temperature at various stages

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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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). Physiological disorders have an important G × E interaction that breeders must take into considerations when designing breeding strategies to improve heat tolerance in lettuce ( Jenni and Hayes, 2010 ; Jenni and Yan, 2009 ). The genetic basis of heat tolerance

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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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Heat accumulation during storage of sod may reach lethal temperatures within 4 days, decreasing sod quality. Treatment with trinexapac-ethyl reduces heat accumulation during sod storage. However, heat tolerance of grasses treated with trinexapacethyl has not been documented. Our objectives were to: 1) determine the lethal temperatures for Kentucky bluegrass (Poa pratensis L.); and 2) identify the effect of a single application of trinexapac-ethyl on heat tolerance. Experimental design was a randomized complete block with three replications and a two (trinexapac-ethyl vs. control) × two (cultivars) factorial arrangement of treatments. Ten days after chemical treatment, Kentucky bluegrass sprigs were exposed to heat stress for 4 days in a temperature gradient block under low vapor pressure deficit. Treatment with trinexapac-ethyl at 0.23 kg·ha-1 reduced heat tolerance. Temperature needed to kill 50% of the population was 35.5 °C for treated vs. 36.1 °C for nontreated grass. Trinexapac-ethyl is in the same chemical family as the cyclohexanedione herbicides that interfere with lipid syntheses in grasses. This may be a reason for the slight decrease in heat tolerance. The practical value of trinexapac-ethyl treatment in reducing heat accumulation during storage of sod may be partially negated by a decrease in heat tolerance. Chemical name used: [(4-cyclopropyl-α-hydroxy-methylene)-3,5-dioxocyclohexanecarboxylic acid methyl ester] (trinexapac-ethyl).

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Abstract

F2 and backcross segregation for heat tolerant × heat sensitive crosses in Chinese cabbage (Brassica campestris L. Group Pekinensis) indicated that heat tolerance was controlled by a single recessive gene.

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Selected breeding lines and cultivars of tomatoes (Lycopersicon esculentrum Mill.) were evaluated for heat tolerance in the greenhouse (39°C day and 28°C night) and field using flowering, fruit-set, yield, fruit quality, and seed production as criteria. Under high temperature, heat tolerant lines performed better than the other two groups in all evaluation criteria except for seed production. The opposite was found under normal field conditions where heat sensitive commercial cultivars outyielded the heat tolerant lines and cultivars. Production of viable seeds under high temperature was severely reduced regardless of the heat tolerance level exhibited by the line or cultivar. Some of the heat tolerant lines could provide valuable sources of plant material for physiological studies to establish the molecular basis of heat tolerance and also could provide excellent germplasm sources for breeding heat tolerant tomato cultivars.

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A greenhouse study was designed to determine the relative heat tolerance of 10 lima bean cultivars and to evaluate the effects of high temperature on lima bean yield. Cultivars were arranged in a randomized complete block with three blocks per treatment. The temperature treatments were 25C day/15C night and 35C day/25C night. Cultivars varied in their response to the higher temperature, allowing for classification into three heat response groups: intolerant, average, and tolerant. Heat-intolerant plants did not experience a significant reduction in number of pods, but number of beans and total bean weight were reduced at the higher temperature. Number of seeds per pod and average weight per bean also tended to decrease in intolerant plants at 35C. In future experiments, these data will be correlated with random amplified DNA (RAPD) markers. These markers will be evaluated for their potential for heat tolerance screening.

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Temperature sensitivity of net photosynthesis (Pn) was evaluated among 4 taxa of rhododendron including Rhododendron hyperythrum, R. russatum, and plants from two populations (northern and southern provenances) of R. catawbiense. Measurements were conducted on individual leaves at temperatures ranging from 15 to 40C. Temperature optima for Pn ranged from a low of ∼21 C for R. russatum to a high of ∼27C for R. hyperythrum. At 40C, Pn rates for R. hyperythrum, R. catawbiense (northern provenance), R. catawbiense (southern provenance), and R. russatum were 7.8, 5.7, 3.5, and 0.2 μmol·m-2·s-1, respectively. R. catawbiense from the southern provenance did not appear to have greater heat tolerance than plants from the northern provenance. There was no difference in temperature sensitivity of dark respiration among the taxa. Variations in heat tolerance among species appeared to result from a combination of stomatal and nonstomatal limitations on Pn at high temperatures.

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