Abstract
Rind temperature of the sunny and shady side of fruits in the sunshine and shade was measured at midday every day. The sunny side of fruits in the sunshine showed much higher than maximum air temperature, being more than 30°C till late November. Whereas, shady parts of every fruits and/or the sunny side of fruits in the sunshine in rainy or cloudy days were nearly equal to maximum air temperature. Average temperature of the sunny side of fruits in the sunshine all through period of the experiment was 5.6 and 8.5°C higher than that of the shady side and maximum air temperature, respectively. Calculating the linear regressions on the rind temperature and maximum air temperature, regression equation and regression coefficient of the sunny side of fruits in the sunshine in fine days was y =0.665x+ 19.02 and r=0.809. The other hand, that of the shady side of them was y=0.849x +7.31 and r=0.974. Difference of the temperature of both side expanded as air temperature became lower.
As surveyed the distribution and diurnal fluctuation of rind temperature on various positions of the fruits to draw the isothermal lines and the maintenance hour of high temperature, the position on the rind that the retention of green color was observed showed remarkable ascent of temperature and had kept high temperature relatively long term in the day time. Rind coloring of citrus fruits proceeds probably along the isothermal lines as the seasonal changes.
In regard to effects of rind temperature of fruits covered or not on coloring, this order was as follows; fruits shaded for Sept. 4 (the beginning of the experiment) to Nov. 17 > shaded for all period of the experiment > in the sunshine for all period > shaded for Nov. 17 to the end of the experiment. The most former passed between 27 and 19°C through all the period. Whereas, the most latter continued to keep high temperature such as more than 28°C till mid November, and after passing at 19°C in late November, furthermore, lowered rind temperature extremely to 11°C in December. Result of the fruit coloring effected by shading period was discussed related to the rind temperature.
