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

Abstract

Young peach trees (var. Okayama-wase) were moved from the open field into the glass house, the windows of which were closed in the day-time and opened in the night, and were exposed to high day-temperature for 31, 62 or 92 days, according to the schedule shown in Table 1. The daily maximum temperature in the glass house was 8_??_13°C higher and the daily minimum temperature 1_??_3°C higher than those in the open (Table 2 and Fig. 1). In the second experiment, young peach (var. Okayama-wase) and Japanese persimmon (var. Hirata-nenashi) trees were treated with high or low day-temperature from December 5 to March 15. The high day-temperature treatment was given by covering the trees with plastic film in the day-time and uncovered in the night. The trees of the low day-temperature treatment were placed on the north side of a large building. The daily maximum temperature around the trees in the high one was 10_??_13°C higher, and in the low one 2_??_4°C lower than those of the open field (Table 4 and Fig. 3). In both experiments, some trees were placed in the cold room of -1 to 0°C for 5_??_7 days for chilling treatment. Bud opening and shoot growth of the trees were observed in the spring, and the following results were obtained. 1. On the peach trees of the high day-temperature treatment, bud opening was delayed and continued over a long period, number of shoots was less, shoot elongation was poor, and apical dominancy was disturbed. The low day-temperature and chilling treatments were effective for hastening the breaking of dormancy of buds (Fig. 4 and Table 5). On the persimmon trees, however, the high day-temperature did not retard the bud opening, and the chilling treatment delayed the spring growth. From these results, it seemed that the day-temperature of December and January in Kôchi was sufficiently low for breaking the dormancy of persimmon buds, but not so low as to be enough for breaking completely the dormancy of peach buds. 2. The high day-temperature treatment in early winter retarded the bud opening of the peach trees, but the same treatment given in late winter hastened the spring growth (Table 3 and Fig. 2). 3. The effect of the high temperature treatment on the bud dormancy reported in the previous paper, which was given throughout the day and night, was more significant than that in this study, though the daily maximum temperature in the previous one was 8_??_12°C lower than in this study. The low night-temperature seemed to be effective on the breaking of bud dormancy.