Effects of temperature on cold acclimation and deacclimation in flower buds of evergreen azaleas

The effects of various storage temperature/duration combinations (5, 10 and 17°/4, 8, 12 and 16 weeks) on cold acclimation and deacclimation of flower buds were studied in four species of evergreen azaleas having different natural distribution and cold hardiness. The freezing process and the exotherm temperature distribution of florets in excised whole buds determined by differential thermal analysis were used as the diagnostics to determine the degree of bud acclimation and deacclimation. The acclimation in buds lasted for as long as 12 to 16 weeks at 5°C storage, and from 8 to 12 weeks at 10°C, and it appeared to be maintained after the chilling requirement for breaking bud dormancy had been satisfied. Therefore, bud acclimation seems to be maintained independently from bud dormancy. The dehardening effect on acclimated buds occurred as a result of short exposures to higher temperatures or long exposures to lower temperatures, and there was no relation between the rate of deacclimation and the degree of hardiness in each species. Among three storage temperatures examined, 5°C was the most effective for the maintenance of cold acclimation in flower buds and the small difference of floret water contents at 5 and 10°C storage is not significant.