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James W. Cross, Stacy A. Bonos, Bingru Huang, and William A. Meyer

overall turf quality of cool-season grasses during summer months is commonly referred to as summer stress. Summer stress can be broken down into two major components, heat stress and drought stress ( Huang et al., 1998a ; Jiang and Huang, 2000 , 2001b

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Fenny Dane, A. Gene Hunter, and Oyette L. Chambliss

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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J. P. Syvertsen and L. G. Albrigo

Abstract

Positional differences among leaf and fruit surface temperatures and water relations of ‘Ruby’ grapefruit (Citrus paradisi Macf.) were related to fruit load and juice quality. Southern top canopy positions experienced the highest temperatures and lower water potentials and yielded more fruit with more soluble solids than other canopy positions. Canopy depth was also an important determinant of fruit yield and early season juice quality. Based on data from 3 trees during 2 seasons, there were greater fruit loads with higher °Brix and lower acidity in the outside canopy positions than in the inside positions. Upper canopy positions tended to have lower acidity and consequently higher °Brix/acid ratios than the lower positions. Abaxial fruit hemispheres were smaller and had a lower percent juice than their paired adaxial fruit hemispheres. Grapefruit from sunlit canopy positions mature earlier than fruit from shaded positions. Since there were more fruit with higher soluble solids in the most exposed canopy positions, daily heat stress and leaf and fruit water stress were not limiting factors in grapefruit yield and juice quality with respect to different tree canopy positions.

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Stephanie Rossi and Bingru Huang

Heat stress is detrimental for cool-season turfgrasses and is characterized symptomatically by a marked decrease in TQ in cool-season turfgrass species as a result of heat-induced leaf senescence. Heat-induced leaf senescence is associated with

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V.M. Russo and J.C. Díaz-Pérez

Heat stress can limit yield in pepper (Capsicum spp.), generally through flower and fruit abortion. A kaolin-based particle film, originally developed to protect fruit trees from insects, has been found to reduce temperatures in tissues of plants. A kaolin-based particle film was tested to determine if it could be used to improve yields of pepper in Oklahoma and Georgia. In Oklahoma, seedlings of a bell pepper, `Jupiter', and a nonpungent jalapeño, `Pace 103', were transplanted at three progressively warmer planting dates from mid-May to mid-July 2002 and 2003, that would ensure that inflorescences would be subject to high day and night temperatures and treated with the kaolin-based particle film. Applications were begun as the first flowers were set and continued through the settings of the first three flushes of flowers on a three-times a week schedule, or on an as needed basis, to determine if the kaolin-based particle film improved yield. In Georgia, the bell peppers `Camelot' and `Heritage VR' were transplanted on 24 Apr. 2003, and treated with the kaolin-based particle film. In addition to yield, physiological measurements and disease incidences were recorded in Georgia. In both locations treatment with water only served as controls. In Georgia, the kaolin-based particle film had no significant effect on net photosynthesis, stomatal conductance, leaf transpiration or leaf temperature, as measured at midday on clear days. In Oklahoma, planting bell pepper after 15 May is not recommended. Planting the nonpungent jalapeño after mid-June can reduce yields. The kaolin-based particle film did not affect yield at either location and is not recommended for use on peppers.

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D. Michael Glenn

); however, reducing canopy temperature can reduce heat stress and increase water use resulting in reduced water use efficiency and increased productivity ( Glenn, 2010 ). The reduction of PAR by the film at the leaf level is compensated in varying degrees

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Abbas Lafta, Germán Sandoya, and Beiquan Mou

differences ( P < 0.0001) among the tested cultivars ( Table 2 ), indicating genetic variation for the traits under heat stress. These data confirmed a previous report of genetic variation for heat tolerance–related traits in eight crisphead lettuce cultivars

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Timothy G. Porch, James R. Smith, James S. Beaver, Phillip D. Griffiths, and Craig H. Canaday

significantly higher seed yield than Montcalm in the Juana Diaz (2004) stress trial ( Table 2 ), whereas TARS-HT2 had a significantly higher seed yield than Montcalm in the 2002 heat stress trial in Jackson, TN, and a significantly higher yield than ‘Redhawk’ in

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Gustavo F. Kreutz, Germán V. Sandoya, Gary K. England, and Wendy Mussoline

trait loci associated with tipburn, heat stress-induced physiological disorders, and maturity traits in crisphead lettuce Theor. Appl. Genet. 126 12 59 70 doi: 10.1007/s00122-013-2193-7 Jenni, S. Yan, W. 2009 Genotype by environment interactions of heat

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Kamal Aberkani, Xiuming Hao, Damien de Halleux, Martine Dorais, Stephen Vineberg, and André Gosselin

fogging systems have been used to prevent plant heat stress during the day. In fact, shading is one of the conventional and familiar techniques used by growers to decrease solar radiation and reduce air and leaf temperatures ( Sandri et al., 2003 ). Many