COLD HARDINESS OF PERSIMMON (DIOSPYROS-KAKI THUNB.) BUDS IN RELATION TO DORMANCY RELEASE AND TEMPERATURE CONDITIONING

Using persimmon (Diospyros kaki cv. Hiratanenashi) buds collected in Y amagata, Kyoto, and Kochi Prefectures in Japan having different climat e, the effect of bud dormancy and temperature conditionings (high temp erature, 25 degrees C; low temperature, 4 degrees C) on the bud cold h ardiness was studied. Additionally, the same temperature conditionings were applied to 'Hiratanenashi' and 'Fuyu' buds whose dormancy releas e was delayed with 100 ppm gibberellic acid (GA(3)). Evaluation of col d hardiness was conducted on the buds using microcomputer-based therma l analysis. The dormancy release of 'Hiratanenashi' bud from Yamagata Prefecture, where mean air temperature during the winter was 2 to 3 de grees C lower than Kyoto and Kochi Prefectures, was completed in late November, whereas that of the other locations occurred in late Decembe r. Irrespective of locations, the buds showed the same seasonal patter n, being hardiest in late January. Neither the low nor the high temper ature conditionings had an effect on the bud cold hardiness during the deep dormant period at all locations. After the release from bud dorm ancy was induced, the high temperature conditioning decreased the bud cold hardiness by a maximum of 4 degrees C, whereas the low temperatur e conditioning increased the bud cold hardiness by a maximum of 1.5 de grees C. Two foliar applications of GA in the fall to 'Hiratanenashi' and 'Fuyu' delayed the release of bud dormancy 12 and 8 days, respecti vely. As with untreated 'Hiratanenashi' buds from different locations, GA-treated 'Hiratanenashi' and 'Fuyu' buds responded to the temperatu re conditionings only after the buds were released from dormancy. Like wise, potted 'Hiratanenashi' trees in Kyoto, subjected to the temperat ure conditionings, did not respond to cold hardiness conditionings unt il the bud dormancy release was completed.