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. (2006) compared the photosynthetic performance of two tall fescue genotypes known to have differing levels of heat tolerance. In this study, ‘Jaguar 3’ (heat-tolerant) and ‘TF 66’ (heat-sensitive) were heat-stressed in growth chambers with day

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Leaf gas exchange of six red raspberry (Rubus idaeus L.) and one blackberry (Rubus L. subgenus Rubus Watson) genotypes growing in 12-L containers was measured at four temperatures (20, 25, 30, and 35 °C) once a month for 3 months in growth chambers by infrared gas analysis. Measurements were taken on three successive leaves on the same primocane between the third and seventh nodes (≈75% to 85% of full leaf expansion). The plants were grown in ambient (field) conditions except when measurements were taken. Maximum daily ambient temperatures rose as high as ≈37 °C during this period. Net CO2 assimilation (A), evapotranspiration (ET), and stomatal conductance (gs ) were measured during June, July, and August. Significant differences (P ≤ 0.01) in A were found among the seven genotypes. 'Arapaho' blackberry displayed the highest mean A rate at all temperatures. Only in the raspberry cultivars Nova and Reveille did the rate of A drop significantly when temperature increased from 20 to 30 °C. 'Reveille' was also the only cultivar in which A significantly declined between 30 and 35 °C. The ET increased significantly over the four temperatures in four cultivars ('Arapaho', 'Heritage', 'Nova', and 'Southland'). The ET rate at 35 °C was higher for 'Arapaho' than for all other cultivars. 'Autumn Bliss', 'Dormanred', and 'Reveille' did not change significantly as the temperature rose from 20 to 35 °C. Stomatal conductance of 'Heritage' and 'Arapaho' did not change significantly between 20 and 35 °C, whereas that of 'Autumn Bliss' and 'Reveille' declined almost 50% when temperature increased to 30 or 35 °C.

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were: 1) to develop and evaluate snap bean populations that combine the Ur-4 and Ur-11 rust resistance genes with heat tolerance; 2) to select from subsequent generations of these populations breeding lines that combine rust resistance (based on the

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fescue. The genetic variation of heat tolerance in fine fescues was determined by Ward’s cluster analysis using TQ, EL, and F v / F m. All 26 fine fescue cultivars were classified into four groups ( Fig. 10 ). Several cultivars with good heat tolerance

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protected cultivation ( Wahid et al., 2007 ). Therefore, breeding cucumber cultivars with thermostability is a useful strategy for improving the heat tolerance of plants (Wahid et al., 2007). Furthermore, the identification and characterization of genes

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response to heat stress under elevated CO 2 with an aim to further understand metabolic mechanisms for elevated CO 2 enhancement of heat tolerance in C 3 perennial grass species. Materials and Methods Plant materials and growth conditions. Sod pieces of

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Abstract

One of the facets of the National Arboretum's landscape plant improvement program is to extend the range of cultivation of the genus Camellia beyond its present limits. Climatic limitations for camellias grown out-of-doors have been the East Coast from Maryland to northern Florida, westward through the Gulf States, and along the West Coast from California to coastal Oregon and Washington. This region, described roughly as the “Camellia Belt”, contains most of the camellias grown in the United States. Beyond this region there are scattered plantings, usually under protected microclimatic conditions. North of this region, plants are subject to severe winter injury, while in the extreme south they are subject to high heat and light intensity. Significant advances have been made in extending the range of camellia culture northward (2, 3). Efforts are also underway to extend camellia culture south of its present limits. The cultivar, ‘Two Marthas’, is the first release coming from this research.

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Selected tomato (Lycopersicon esculentum Mill) genotypes were evaluated for their fruit-setting ability under high-temperature field conditions. A temperature-controlled greenhouse study was conducted to determine the percent fruit set from the total number of flowers and fruit produced per plant. Ratings for set obtained under high-temperature field conditions were significantly (P = 0.001) correlated with percent fruit set determined under similar greenhouse conditions. Most of the Asian Vegetable Research and Development Center (AVRDC) selections, Beaverlodge lines, `Nagcarlan', and `Red Cherry' could be considered heat-tolerant. Small-fruited, abundantly flowering genotypes were less affected by heat stress than larger-fruited cultivars. Prolonged periods of high temperature caused drastic reductions in pollen fertility in most genotypes, except `Red Cherry' and L. esculentum var. cerasiforme (PI 190256). Stigma browning and stigma exsertion commonly occurred on all lines, except AVRDC CL-5915-553 and PI 190256. Diallel analyses indicated that pollen fertility and fruit set under high field temperatures were primarily under additive gene control.

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