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

to detect differences among cultivars with known differences in summer landscape performances (unpublished data). After 1 h of heat stress, leaf samples were collected to be used in relative injury (RI) and morphological analyses. Relative injury. The

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Ching-Hsueh Wang, Der-Ming Yeh and Chian-Shinn Sheu

that, for summer- and fall-flowering chrysanthemum cultivars, those having a low relative injury value coincide with the greater CMT and shorter heat-induced delay to flowering in field conditions ( Yeh and Lin, 2003 ). Little information on CMT in

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Neil O. Anderson, Mi-kyoung Won and Dong-chan Kim

-43 ( Fig. 2A) ]. Fig. 2. Effects of water bath temperatures on relative injury (RI) of garden chrysanthemum leaves of 10 genotypes when grown under two temperature and two photoperiod conditions [key legend: high temperature short days (HTSD); high

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D.M. Yeh and H.F. Lin

Identification of heat-tolerant chrysanthemum [Dendranthema ×grandifolia (Ramat.) Kitamura] genotypes for commercial production in hot areas of the world is desirable. The extent to which electrolyte leakage from chrysanthemum leaf discs, measured using a test for cell membrane thermostability (CMT), could be related to the delay in flowering induced by heat in the field-grown plants was determined. The relationship between the relative injury (RI) occurring in leaf tissue discs of chrysanthemum cultivars and treatment temperature was sigmoidal. A single temperature treatment at 50 °C resulted in injury values near the midpoint of the sigmoidal response curve and showed the greatest sensitivity in detecting genotypic differences in heat tolerance. The cultivars with a low RI value are those with the greater CMT and shorter heat-induced delay to flowering.

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Suzanne S. McDonald and Douglas D. Archbold

The effect of dehydration stress on membrane competence among and within Fragaria species was evaluated using index of injury, Id, and tissue ionic conductance, gTi. Single accessions of F. chiloensis ssp. lucida Duch., F. virginiana ssp. glauca (S. Watson) Staudt, F. virginiana ssp. virginiana Duch., F. ×ananassa Duch., and F. vesca L. were used to study interspecific variation. Leaf thickness and total electrolyte content were greatest for the F. chiloensis ssp. lucida accession and least for the F. virginiana ssp. glauca accession, but foliar electrolyte concentration did not vary across accessions. The gTi values were >5-fold higher from 0 to 2 hours than for other intervals, declining over time. Significant differences in gTi and Id values were only evident at 2 and 4 hours within stress levels, and increased as stress level increased. While the F. chiloensis ssp. lucida accession exhibited low gTi values at 70% relative water content (RWC), it showed greater relative membrane injury than the other species expressed as gTi, Id, or the ratio of stress gTi to control gTi as dehydration level increased. Although the F. virginiana ssp. glauca accession had the highest gTi values, even at 100% RWC, its relative injury as stress level increased was not as great as that of the F. chiloensis accession. In a second experiment, intraspecific variation was examined using four accessions each of F. chiloensis and of F. virginiana which were dehydrated to 50% RWC. The species mean gTi, Id, and gTi ratio values at 2 and 4 hours for the F. chiloensis accessions were lower than those for the F. virginiana accessions, but significant intraspecific variation was also observed. In spite of the differences between species means, the evidence of intraspecific variation indicates that not all accessions of a species exhibit similar drought responses (i.e., membrane competence). Due to the consistent conclusions derived from using either gTi or Id after 2 or 4 hours of incubation for characterization of membrane competence, gTi and Id were comparable techniques for identification of potential drought tolerance in Fragaria.

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Wei-Ling Chen, Cheng-Hung Hsiao and Hsueh-Shih Lin

method to evaluate heat tolerance in plants ( Wu and Waller, 1983 ). Relative injury (RI) induced by 30 min of temperature treatment was calculated as follows: RI (%) = {1 − [1 − ( T i / T f )]/[1 − ( C i / C f )]} × 100, where T and C refer to the

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ornamental pepper cultivars. In addition, relative injury was estimated using leaf cell membrane thermostability tests. From the modified bilinear temperature-pollen germination and tube length response functions, cardinal temperatures (T min , T opt , and T