Freezing Tolerance of Several Diospyros Species and Kaki Cultivars as Related to Anthocyanin Formation

Abstract

The freezing resistances of three Diospyros species and three cultivars of D. kaki were evalu- ated by survival of twigs and electrolyte leakage from the tissues after freezing treatments. Dormant 1-year-old twigs were cooled from -5° to -5°- 30°C within 5 hr, maintained at each temperature for 5 hr and thawed gradually to 5°C for 5 hr. The twigs soaked in water were held for 20 days under 20°C to determine recovery.
The hardiest species during the coldest period of the season was D. lotus followed by D. kaki, and the least hardy was D. taitoensis which is distributed in subtropical Taiwan. The critical low temperatures that did not injure the plants were -10°C for D. taitoensis, -15°C for D. kaki and -20°C for D. lotus; the temperatures at which half of the test twigs was killed (LT₅₀) were - 12°, -20° and -25°C, respectively. Their electrolyte leakage at LT₅₀ ranged from 25 to 28%.
Among three cultivars of D. kaki, Eiratanenashi' which is native to the northern region of Japan, was most tolerant to freezing during mid-winter ("true freezing resistance"), however, it was the most sensitive to freezing before cold acclimation in early autumn and after cold acclimation in spring.
Starch hydrolyzed to sugars in twigs of three cultivars of D. kaki under natural conditions during mid-winter. A close relation was found between the freezing resistance, evaluated by electrolyte leakage from twig cells, and anthocyanin in the cortical tissues. Anthocyanin con- tents in cortical tissues reached a maximum in mid-February; the pigment levels tended to increase when plants were exposed to -10°- 30°C which were below the ambient tem- perature. Moreover, anthocyanin contents in the cortex decreased, and the twigs became less hardy by the deacclimation treatment during the coldest part of the season. Conversely, twigs under the chilling treatment before cold acclimation in early autumn became hardy; the change was accompanied by an elevation of anthocyanin content.