Influence of winter temperature on the dormancy of some deciduous fruit trees. I

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The experiments were carried out to clarify the causes of un-uniformity of time of bud-opening, decrease of number of buds opened, and of decre-ase of shoot-growth in some deciduous fruit trees after warm winter in Kochi prefecture. Young trees of Japanese persimmon (var. Hiratanenashi grafted on Diospyros Lotus seedling), peach (var. Okayamawase on Prunus persica seedling) and of Japanese pear (var. Yakumo on Pyrus serotina seedling) were brought into thermo-static dark rooms, in which the air temperature was maintained at -1_??_0°C, 8_??_11°C and 18_??_23°C, respectively, and they were kept there for 888 hours, 1368 hours or 1992 hours since December 2, 1954 successively, and thereafter they were transfered to warm room (18_??_23°C). When the minimum temperature in the open air became more than 15°C, they were carried out to the open air. At any condition, such as cold (-1_??_0°C), mild (8_??_11°C), or warm (18_??_23°C) winter condition, the root-growth of Japanese persimmon occurred after their buds opened and their shoots developed, as in the natural condition of Japan. Their bud-opening time was December 28 in the warm condition, February 16 in the mild, March 15 in the cold, and February 28 in the natural condition. Japanese persimmon had rather longer growth period and grew better owing to the higher winter temperature. The growth cycle of peach and Japanese pear were varied owing to the winter temperature. In the natural condition, buds of peach and Japanese pear opened on the begining of March, after their root-growth on the end of February. In the cold condition, their root-growth were retarded, namely, whereas their buds opened on the begining of March their roots began to elongate on the begining or the middle of March. In the mild condition, their bud-opening and root-growth in spring were retarded, i.e., bigan on the middle of March, and their growth were poor. On the other hand, only one or two buds opended on the end of December in warm condition, and their shoot-development were. retarded, but their root-growth occurred on the be-gining or the middle of January. So, when the air temperature was not cold for some period at least in winter, the bud-opening of peach and Japanese pear were retarded and their growth were poor. When the temperature has been maintained at -1_??_0°C for 888_??_1992 hours since December 2 successively, the number of opened buds increased. This phenomenon was conspicuous on peach and Japanese pear. And many buds of peach and Japanese pear opened uniformly in short time showing the apical dominance, but the bud-opening of Japanese persimmon was retarded under the above condition. And only small number of buds of peach and Japan-ese pear opened slowly showing not the apical dominance, when they were kept at 8_??_11°C, but the bud-opening of Japanese persimmon was hurried up showing the apical dominance under the same condition. When the temperature was 18_??_23°C during the whole winter, only one or two buds opened at the tip of shoot in peach and Japanese pear. The dormancy of peach and Japanese pear were completed owing to the low temperature(-1_??_0°C) for 888 hours since December 2 successively, but the dormancy of Japanese persimmon was complete even after encountered with such mild temperature as 8_??_11°C for the same period. Total hours of duration of temperature below zero in southern district of Kochi prefecture were 154 hours in winter from 1953 to 1954, 210 hours in winter from 1954 to 1955. It is said that 1000 to 1200 hours of duration of the temperature below 7.2°C is necessary for breaking dormancy of peach, and 1400_??_1800 hours on Japanese pear. In the southern district of Kochi, total hours of duration of the temperature below 7°C were 817 and 1002 hours in the winter 1953_??_1954, 1954_??_1955, respectively