This paper deals with the influence of irrigation on diurnal fluctuation of fruit diameter, size and quality of harvested fruit of the Nijusseiki pear. Moreover, the effects of bagging combined with irrigation on fruit growth behavior was studied.
The results obtained are summarized as follows:
1) Under dry and high temperature condition in late August, when the proper amount of water, 90
l per tree, was supplied every day, the contraction of fruit diameter in the daytime was remarkably reduced, however, the daily growth and the amplitude of fluctuation in fruit size were hardly affected. Excessive irrigation (360
l per tree) resulted in severe daily contraction as compared with that of non-irrigated fruits or controls, and a remarkable decrease in daily growth and reduction of the amplitude of fluctuation.
2) Continuous measurement on daily change of fruit size after irrigation in late August revealed that the growth of fruit was advanced to large extent on the night following the irrigation. After that, however, it decreased to the same rate as that of controls, and consequently little difference in cumulative growth increment during the three days was obtained between irrigated and non-irrigated plots.
When treated with excessive irrigation, the fruit showed no contraction but remarkable enlargement in the daytime immediately after the irrigation. After the next day, however, extreme contraction occurred, and the nocturnal enlargement amounted to only enough to recover from the daily contraction, and thus total growth was inferior to that for other treatments.
3) In cace of suitable water supply, the size, appearance, and quality of fruit were most desirable, though fruit maturation was delayed a little. Size and appearance for non-irrigated fruit were poorer and free acid content was higher than for irrigated fruit.
Excessively irrigated trees produced fruits of intermediate size with the lowest soluble solid content, and often displaying a disordered peel with an uneven rough. surface which is usually called “yuzuhada”.
4) In general, daily irrigation time had little influence on diurnal fluctuation in fruit diameter. Growth rate of fruit, however, was slightly higher in the twice (morning and evening) irrigated trees, which was followed by trees with one time (evening or morning) irrigation.
5) Harvested fruit size was largest for the twice irrigated plot and smallest for the morning irrigated one, while soluble solid content was highest in the latter and lowest in the former. Free acid content was remarkably higher for the non-irrigated plot as compared with the irrigated plots, among which little difference was displayed.
6) As for the effect of irrigation together with fruit bagging on diurnal fluctuation of fruit diameter, from late June to early July the contraction in the daytime was considerably increased by irrigation and the fruit growth was also increased by five to six percent regardless of bagging.
In late August, contraction became smaller with bagging, and this tendency was much more emphasized by irrigation. The bagged fruit showed small variation in the degree of diurnal fluctuation between the irrigated and non-irrigated plots. On the other hand, the daily growth of unbagged fruit was greatly accelerated by irrigation, and consequently their cumulative increment in three days was threefold as great as that for non-irrigated ones.
Fruit temperature rose excessively in the non-irrigated and non-bagged plot in the daytime of this hot season, especially for the fruits exposed to sunlight.
7) Observing the pattern of diurnal fluctuation in fruit diameter at the middle of September, the fruit developing stage was set back by irrigation. Thus, as the result, the maturation of non-bagged fruit was earliest for the non-irrigated plot.
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