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Hongwen Huang, Shengmei Wang, Renhuang Huang, Zhengwang Jiang, and Zhonghui Zhang

'Jintao' is a new yellow-fleshed kiwifruit (Actinidia chinensis Planch) developed from the breeding program at the Wuhan Institute of Botany (WIB), in Wuhan, Hubei, People's Republic of China. 'Jintao' is a midseason cultivar that ripens three to four weeks before the standard commercial cultivar [A. deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson] 'Hayward'. It is sweeter than 'Hayward' and has a smooth skin. 'Jintao' was selected from A. chinensis and offers growers in warmer climates an alternative to 'Hayward', because of its higher productivity, better fruit quality, and improved heat tolerance. 'Jintao', which means golden peach in Chinese, is named in recognition of its yellow flesh and the common Chinese name, Mihou-tao, or monkey peach.

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John Frett, W. Edward Kee, and Stephen Redcay

Lima bean yields are lower in Delaware than in other lima-bean-producing states. One of the factors that contributes to the low production is the high temperatures that occur during production. Six commercial varieties of lima beans, both fordhook and baby lima bean types, were grown in a glass greenhouse at either 25C or 35C daytime temperatures to screen for heat tolerance. Plants grown at high temperature were typically shorter and more bushy than plants grown at 25C. Few, if any, buds, flowers, or early pods remained on plants at harvest if the plants were grown at 25C, while plants grown at 35C were still producing buds and flowers. Lima bean yields were generally reduced at 35C. The magnitude of the effect on yield ranged from `F1072', which had a 100-fold decrease in yield, to `Early Thorogreen', which demonstrated a slight increase in yield in response to increased temperatures.

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Aref A. Abdul-Baki and John R. Stommel

Heat-tolerant and -sensitive Lycopersicon esculentum Mill. and L. pimpinellifolium (Jusl.) Mill. genotypes were grown in the greenhouse under optimum- (27/23C, day/night) and high-temperature (35/23C) stress regimes. Heat tolerance levels in the genotypes were established by determining percent fruit set at high and optimum temperatures. Under optimum temperature, fruit set ranged from 41% to 84% and from 45% to 91% in the heat-sensitive and heat-tolerant genotypes, respectively. Under high temperature, no fruit set in the most heat-sensitive genotypes. Fruit set in the heat-tolerant genotypes ranged from 45% to 65%. In vitro germination and tube growth of pollen taken from genotypes grown under optimum temperature conditions were determined before and after subjecting the pollen to 45C for 1, 2, and 4 hours. The response of pollen to heat treatments was genotype dependent and not a general predictor of fruit set under high-temperature stress.

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Karl J. Sauter, David W. Davis, Paul H. Li, and I.S. Wallerstein

Yield in common bean, Phaseolus vulgaris L., can be significantly reduced by high temperature (I-IT) during bloom. Ethylene production from plant tissue increases as a consequence of various stresses, including heat stress. The inheritance of leaf ethylene evolution rate (EER) of HT-stressed (35/30C day/night) progenies from crosses among bean genotypes previously categorized as HT sensitive or tolerant, based on cell electrolyte leakage, was investigated. Evidence from generation means analysis of Fl, F2, and backcross progenies shows EER to be genetically controlled, with additive, dominance, and epistatic effects indicated for low EER. The range (0.62 to 2.52 μg-1·hr-1) of EER from field-grown lines and cultivars suggests the existence of considerable genetic variability. EER was associated (r = –0.70) with heat tolerance, as estimated by cell electrolyte; leakage.

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Jeffrey Anderson, Greg McCollum, and Warren Roberts

Electrolyte leakage was used to quantify heat stress injury in `Early Calwonder' pepper (Capsicum annuum L.) leaf disks. Lethal temperatures were estimated from the midpoint of the sigmoidal response curve. An interaction between exposure temperature and duration was observed, with lethal temperatures decreasing linearly from 53 to 46C as exposure duration increased exponentially from 5 to 240 min. Exposure to two 7.5-min periods at 51.5C, interrupted by 4 hours at 21C, resulted in the same injury as a continuous 15-min exposure to 51.5C. Plants grown at 22/20C day/night cycles and held 24 hours at 38/30C had increased their heat tolerance by 3C, 51 to 54C; these plants reacclimated to 52C 48 hours after having been transferred back to 22/20C. Leaf disks acclimated significantly in vitro in 1 hour and were fully acclimated by 4 hours at 38C.

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A.M. Shirazi and G.H. Ware

The high resistance of Chinese elms to Dutch elm disease and elm leaf beetles makes them excellent trees for the urban landscape. There are many new Chinese elms being developed through the tree breeding program at The Morton Arboretum. Many new elms are already on the market or will be available soon from nurseries. There is little known about the stress tolerance, e.g., cold, heat, drought, etc., of new elms from China. The objectives of this study were 1) to determine the midwinter cold hardiness of new Chinese elms and 2) to determine the leaf heat tolerance and stem cold hardiness of new elms from the nursery. The stem cold hardiness of nine new elms from China was evaluated in Feb. 1998 and 1999 from the elm breeding program at The Morton Arboretum by using an artificial freezing test. The LT50 (the temperature at which 50% of the tissues were killed) of the most to least hardy genuses for Feb. 1998 were Ulmus macrocarpa (> -36 °C), U. wilsoniana # 673 (-34 °C), U. parvifolia R-89-120 (-34 °C), U. wilsoniana # 669 (-34 °C), U. wilsoniana # 997 (-33.8 °C), U. szechuanica (-30 °C), U. gaussenii R-94-85D (-30.7 °C), U. bergmanniana var. lasiophylla R-9422SD (-27.7 °C), and U. castaneifolia #R-9411-11-SD (-25.9 °C). Four new elms from Schmidt Nursery, Boring, Ore., were also evaluated for leaf heat tolerance in August and cold hardiness in Dec. 1998 and Feb. 1999. The LT50 of cold hardiness of stem tissues of cultivars in December were U. parvifolia `Emer 1' P.P. 7551, Athena® elm (-23.5 °C), U. parvifolia `Emer 1' P.P. 7552 Allee® (-26.5 °C), U. Accolade™ (-33.5 °C), and U. Danada Charm™ elm (-31 °C). The LT50 of the most to least heat-tolerant cultivars were U. parvifolia `Emer 1' P.P. 7551, Athena® elm (53.8 °C), U. parvifolia `Emer 1' P.P. 7552 Allee® (52.1 °C), U. Accolade™ (50.8 °C), and U. Danada Charm™ elm (50.6 °C). Growth, dormancy development, spring budbreak, and performance of these cultivars will be compared.

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Thomas G. Ranney, John M. Ruter, and Clifford D. Ruth

Temperature sensitivity of net photosynthesis (PSN), dark respiration, and chlorophyll fluorescence was evaluated among three taxa of hollies including I. aquifolium, I. cornuta, and I. rugosa. Variations in foliar heat tolerance among these species were expressed as differential temperature responses for PSN. Temperature optima for PSN was 22.0, 26.3 and 27.9 umol·m–2·s–1 for I. rugosa, I. cornuta, and I. aquifolium, respectively. Differences in temperature optima for PSN and thermotolerance of PSN appeared to result from a combination of stomatal and nonstomatal limitations. At 40°C, potential photosynthetic capacity, measured under saturating CO2, was 4.1, 9.4, and 14.8 μmol·m–2·s–1 for I. rugosa, I. aquifolium, and I. cornuta, respectively. Based on these results, I. rugosa was identified as the most heat-sensitive species followed by I. aquifolium then I. cornuta. Comparative tolerance to root-zone inundation was evaluated among 14 holly taxa. Following 8 weeks of flooding, four of the taxa: I. cornuta `Burfordii', I. × `Nellie R. Stevens', I. cassine, and I. × attenuata `Foster's #2' performed remarkably well during and after flooding with photosynthetic rates > 40% of the controls, root ratings >75% of the controls, <5% of the foliage showing deterioration, and 100% survival. Conversely, I. crenata `Convexa', Ilex × meserveae `Blue Princess', I. rugosa and I. aquifolium `Sparkler' did not tolerate flooding well as indicated by severely depressed photosynthetic rates, deterioration of foliage and roots, and decreased survival. The remaining taxa were intermediate.0

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David J. Weston*, David J. Weston, Ginger A. Swire-Clark, and Wm. Vance Baird

Rubisco, the primary enzyme governing carbon assimilation, is dependent upon Rubisco activase. The heat sensitivity of activase, including its expression and thermal stability, varies among species and is considered a key component governing photosynthetic performance in response to moderate heat stress (32-35 °C). However, the Rubsico-Rubsico activase association has yet to be examined among woody plants or varieties within a species, the understanding of which will assist cultivar improvement strategies. Using molecular and physiological techniques to study the role of activase in thermal regulation of photosynthesis, we found that net photosynthesis decreased in Acer rubrum L. `Northwood' at 31°C, whereas the southern variety, A. rubrum `Florida Flame', maintained optimal assimilation rates up to 36 °C. Additionally, the maximal carboxylation rate of Rubisco (Vcmax) at 35 °C was 31.7% lower for Northwood in comparison to Florida Flame. The cloned activase sequences from both cultivars show 97% nucleotide homology and 98% amino acid identity, indicating the potential for similar protein product formation and function. Interestingly, sequence analysis indicates that both cultivars produce at least two isoforms of activase derived from alternative transcript splicing. We will discuss activase mRNA processing and protein isoform abundance in relation to Rubisco kinetic properties as a function of heat tolerance in these two thermally contrasting woody plant genotypes.

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Gregory Welbaum and Charlie O'Dell

Greenhouse grown transplants of 23 lettuce varieties were produced in 1” diameter speedling flats, seeded May 1, transplanted to the field in early June when plants were 4 weeks of age. Transplants were grown in a commercial potting media of peat-vermiculite-perlite. Loose leaf, butterhead, crispbead or iceberg and cos types were included, field-planted at the Elam Swarey farm in Burkes Garden, Tazewell County, Virginia, at an elevation of 3,400 ft. above sea level. No crisphead (iceberg) varieties were found to be satisfactory in yield or quality for area conditions. Of loose leaf varieties, `New Red Fire' and `Red sails' were judged highly adapted for high elevation summer production at sites above 2,000' elevation and/or for fall production at lower Piedmont and coastal areas for October and November harvests. `Tiara', a dark green loose leaf was judged the best of its type in this test. Of the cos types, `Pyramid' and `Ideas' were best adapted to high elevation summer production or lower elevations fall production. Of the butterhead types, `Condor' and `Encore' were suited to higher elevations, `Condor' showing more heat tolerance.

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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.