Influence of Freeze Acclimation Procedure on Survival and Regrowth of Container-grown Campanula takesimana Nakai.

Abstract

Crown divisions of Campanula takesimana were potted 1 Sept. 1994 and were grown under natural conditions until 19 Nov., when they were moved into a 3 °C greenhouse. On 15 Feb. 1995, 10 plants were randomly assigned to each of four temperature treatments (−5, −8, −11, and −14 °C), using each of four freeze acclimation procedures designated A through D: group A plants were held at treatment temperatures for 30 minutes; group B plants were first subjected to three alternating freeze-thaw cycles (−3 °C for 24 hours, 3 °C for 24 hours), then held at treatment temperatures for 30 min; plants in group C were held at −1 °C for 14 days and subsequently were exposed to treatment temperatures for 30 minutes; group D plants were held at treatment temperatures for 48 hours. A control group was held at 3 °C for the duration of the study. Following 6 weeks regrowth at 15 °C, plants were rated for survival and regrowth quality relative to unfrozen controls. At treatment temperatures of −8 °C and less, acclimation procedure significantly influenced survival and regrowth quality. Plants exposed to three freeze-thaw cycles had the highest regrowth ratings at treatment temperatures less than −5 °C, with no loss in marketability following exposure to −11 °C. In addition, all plants exposed to freeze-thaw cycles thrived following controlled freezing, whereas those in each of the other groups displayed a decline in survival with decreasing treatment temperatures. Holding plants for 14 d at −1 °C had no beneficial effect on survival or regrowth quality relative to plants held at constant above-freezing temperatures. Increasing exposure duration from 30 minutes to 48 hours significantly reduced regrowth quality at treatment temperatures of −8 °C and −11 °C.