1975 Volume 43 Issue 4 Pages 359-367
In the first paper of this series (6), it was reported that contraction of fruit size in the daytime was not observed on a rainy day, and, thus, the diurnal fluctuation of fruit size seemed to be closely related to the daily change of atmospheric humidity. Under moist soil conditions, however, fruit growth was not influenced by atmos-pheric humidity, which indicates that under these conditions the atmospheric humidity was not a dominant factor as to the fruit growth. In the present paper, the influence of aerial moisture on diurnal fluctuation of fruit size was investigated as an environmental factor.
In 1968, daily change in the equatorial diameter of bagged and exposed fruits on ten-year-old Wase Nijusseiki (early type) and Nijusseiki (common type) pear trees grown in the orchard was examined under rainy conditions. Besides, the influence of water sprinkling on diurnal fluctuation of fruit was also examined with ten-year -old Wase Nijusseiki pear trees on July 31, August 4 and 11.
The results obtained are summarized as follows
1)Under rainy conditions the size of exposed fruits was superior to that of bagged ones. The influence of rainfall was immediately exerted on the size of exposed fruit, while about two hours later it was confirmed on the bagged fruit.
When it rained after a sequence of droughty days, cracking was brought about on many fruits unless they had been covered with bags.
2) Soon after the beginning of sprinkling, fruit diameter of sprinkled trees enlarged excessively, instead of contraction which was usually observed in the daytime. So the pattern of diurnal fluctuation in fruit diameter was like that of rainy day. The diurnal enlargement of bag-removed fruits was twice as great as that of bagged fruits, and consequently seven in ten measured fruits were cracked by moisture inhibition.
The increment of water content in the bag-removed fruit amounted to twice that of the bagged fruit. Thus many injured fruits were brought about because the growth in volume of hypodermal tissue was extremely rapid due to the absorption of water through its surface.
3) Relative daily growth in fruit transverse diameter of sprinkled trees was 116.1, 154.3, and 130.2, in July 31, August 4 and August 11, respectively, as indicated by the non-sprinkled fruit of 100. As to the weight of harvested fruit, however, the difference was not significant among the treatments. So, the extreme fruit growth on the sprinkling day seems to be due to a temporary effect.
4) No difference in soluble solids, free acid, and maturation time of fruit was also observed between sprinkled and control plots.
5) The temperature of air, fruit and leaf inside the tree crown was lower in sprinkled than in non-sprinkled trees. Atmospheric humidity, on the contrary, was higher in sprinkled than in not-sprinkled trees.