Root membrane thermostability of Cornus florida L. provenances

Flowering dogwood seed collected from native trees in 3 USDA Hardiness Zone s (6b, 7a, and 8a; American Horticultural Society (AHS) Heat-Zones 7, 7, an d 8, respectively) were germinated and grown in containers prior to laborat ory procedures to determine root cell membrane thermostability. Unsuberized , current season, fine root tissues were subjected to temperatures ranging from 20 to 60 degrees C for 30 min and analyzed for cellular electrolyte le akage. Electrolyte leakage from root tissue exhibited a sigmoidal response to temperature for trees from each location. Critical midpoint temperature (T-m) was greater for seedlings native to USDA Hardiness Zone 6b (AHS Heat- Zone 7), 52.4 +/- 0.6 degrees C, than T-m for seedlings originating from US DA Zone 7a (AHS Zone 7), 51.2 +/- 0.5 degrees C. However, seedlings from US DA Zone 8a (AHS Zone 8), at 51.5 +/- 0.4 degrees C, were similar to those c ollected in USDA Zones 6b (AHS Zone7) and 7a (AHS Zone 7). The results of t his study find little genetic variability across this part of the native ra nge of flowering dogwood regarding root thermotolerance. Although differenc es between two provenances were found, these differences may be of little e cological significance. (C) 1999 Elsevier Science Ltd. All rights reserved.