和ナシ果実の日肥大周期に関する研究 (第7報)

Abstract

Several articles (8, 13, 14, 16, 17, 22, 29, 30, 31, 32, 33, 34) have been reported on the effect of bagging on characteristics of pear fruit. In the previous reports of this series (5, 6) some results have been announced concerning the influence of rainfall and irrigation during a dry season with high temperatures on daily change in size of bagged and un-bagged fruit and also on the quality of harvested fruit.The present experiment was performed to confirm the effects of bagging with different kinds of paper, such as paraffin-coated paper and newspaper, on the diurnal fluctuation, size and quality of fruit using ten and eleven-year-old Shinseiki pear trees.Results obtained are described as follows:1) Though little influence on diurnal fluctuation in fruit diameter was observed with paper bags, in the earliest stage before the middle of June the rate of growth was highest in fruit enclosed with paraffin paper bags. During the later stage of fruit development, however, the un-bagged fruit slightly excelled over the bagged fruit in growth. Consequently the former showed similar size to the latter at harvest, though the fruit in the newspaper bag was a littler larger than that of the others.2) Variation in fruit temperature was marked in the daytime. On June 11, 1968 a maximum temperature of 30°C was attained in the fruit enclosed with the paraffin paper bag, and 27.5°C with the newspaper bag: they were remarkably high as compared with the controls of 25.5°C. On August 12, a fine day of high temperature, the maximum temperature of the open air rose to 32.7°C, and under the condition of being exposed directly to sunlight, fruit temperature attained 36.0°C in the controls, 34.0°C in the newspaper bag (2.5°C lower than the air temperature inside the bag), and 44.0°C in the paraffin paper bag (9.0°C higher than the air temperature inside the bag).3) In general, the relative humidity inside the paraffin paper bag in the daytime was much higher than that of the open air. The difference of the humidity between inside and outside the bags was 38 percent at the maximum temperature. On the other hand, in the newspaper bag the change of the moisture condition directly reflected that of the outside air through the bag paper. Namely, moisture retention of the latter bag was inferior to that of the former bag.4) Although in the early stage sugar content was highest in fruit bagged with paraffin paper, at maturity it was lowest for it and highest for the non-bagged fruit. Non-reducing sugar content at harvest was highest for the fruit with newspaper bagging amongst all the treatments.5) The ratio of fruit diameter increment during the latter stage (from June 21 to the harvest time) to the diameter of the harvest time, was larger in un-bagged than in bagged fruits. This tendency was shown remarkably in 1969 when higher temperatures and longer cumulative hours of sunshine were found during the period of the later fruit developmental stage than for an ordinary year. It can be reasonably assumed that under such a high temperature condition bagged fruit was affected in its growth by the excessively high temperature inside the bag, especially in the paraffin-coated paper bag.6) During the early stage of fruit growth, when the air temperature did not rise high enough to inhibit the fruit development, bagging, especially using paraffin paper bag, showed a favourable effect on the fruit growth because it resulted in better thermal conditions. During the later stage, however, the temperature of the fruit rose rapidly to the excessive level of about 40°C, when bagged with paraffin paper exposed directly to the sunshine. Thus, in this stage, extremely high temperature caused by the bagging inhibited the growth and accumulation of sugars in the fruit.