和ナシ果実の日肥大周期に関する研究 (第2報)

Abstract

In the previous paper significant correlations were reported between air temperature and diurnal increment or diurnal amplitude of fruit growth at Stage I. In the present investigation, young fruits of Nijusseiki pear were grown under different night temperature conditions, and effects of night temperature on the diurnal fluctuation of fruit diameter, mostly of transverse one, changes in organic components of fruit, period of maturation, and quality of harvested fruit were examined.Night temperatures were regulated at 15, 20, and 30°C during the period of 65 days from fruit set to June 29. Trees exposed to natural temperature conditions served as controls. The results obtained are described as follows:1) High night temperature exerted more prominent effects on the diurnal fluctuation of fruit diameter at the time of a month after anthesis (about May 25) than at the other periods of growth. The higher the night temperature the greater the amplitude of diurnal fluctuation (both expansion and contraction). These effects were more marked at earlier than at later stages of fruit development and they became more vague as the time progressed.2) The higher the night temperature the more shortened the duration of the former half of fruit development (Stages I and II), and a distinct demarcation period from Stage I to Stage II was observed. Duration of fruit development at Stage I was 46, 44, 41, and 31 days in controls and 15, 20, and 30°C treatments, respectively, that is, decrease in maturing period was 5, 15, and 30 days in the 15, 20, anb 30°C night temperature treatments, respectively.3) In the 30°C treatment, high night temperature at early stages of fruit development stimulated the metabolism of organic components within the fruit, which may be due mainly to the maturation of fruit. Before the maturation period, the surface of the peel was kept quite smooth. The size of fruits harvested was uneven and most of them reached maturity with small sizes. Below 20°C, higher night temperature seemed to produce fruit of rather superior quality. In general, fruit exposed to night temperature of 20°C were most excelent in size, exterior appearance, and internal quality, though the maturing period (duration of development from fruit set to harvest) was not so shortened.4) At a later period of fruit development, after Stage III, diurnal fluctuation of fruit diameter reflected the internal physiological features such as accumulation of elaborated materials and conversion of sucrose into inverted sugars. The relation between external phenomena and internal metabolic activity seems to be meaningful from the viewpoint of fruit development. When both the diurnal growth and the contraction of fruit diameter were prominent, more reducing sugars were accumulated within the fruit, whereas nonreducing sugar (sucrose) was predominantly accumulated when the contraction was gradually diminished and finally stagnated.