Effects of temperature on flower development and fruit set of 'Satohnishiki' sweet cherry

Effects of temperature on flower development and fruit set of 'Satohnishiki' sweet cherry were studied. 1. Trees were grown in sunlit growth chambers controlled at 10, 15, 20, and 25 degrees C during the day and grown under field condition at night (average minimum temperature during treatment was 7.7 degrees C) from one month before anthesis to petal fall. The high temperature hastened blooming but markedly reduced flower size. When flowers were hand-pollinated with pollen of 'Takasago', the fruit set at 10, 15, 20, and 25 degrees C were 36, 50, 29, and 2%, respectively. 2. In another experiment, the anatomical characteristics of flowers were compared between the trees grown in low temperature regime; 10 to 15 degrees C during the day/natural temperature at night (average minimum temperature during treatment was 5.4 degrees C) and those grown in high temperature regime; 20 to 25 degrees C during the day/10 to 15 degrees C at night from one month before anthesis to petal fall. High temperature suppressed ovary growth and induced small ovules and nucelli. At anthesis, most of the embryo sacs were still immature in both temperature regimes. At high temperature, the nucelli and embryo sacs degenerated rapidly thereafter, At low temperature, the embryo sac development continued so that 48% of the embryo sacs reached the eight-nucleate stage two days after anthesis. These results reveal that the rapid degeneration of embryo sac and nucellus is a major reason for the reduction in fruit set when the developing buds are exposed to high temperatures.