Abstract
We conducted a field survey to determine the causes of rice leaf injury observed in rice paddy field located in hilly and mountainous northern regions of Nagasaki. (1) Solar radiation in the mountainous region where the rice “hakare” symptom occurred was about 20% lower than that of the low altitudes. (2) The top / root ratio of the rice plant (dry weight basis) was higher in the injured rice than that with normal growth. (3) Our results suggest that delaying the time of transplanting than the conventional cultivation reduces the occurrence of rice “hakare” symptom. (4) With the approaching of low pressure system at the end of rainy season, the local dry wind blows up in the mountainous rice paddy areas and the difference in temperature and humidity between high and low altitudes become larger. From the above, we concluded that rice “hakare” symptom occurs as a result of the following factors. The imbalance growth between the above-ground and underground parts of the rice plant due to the shortage of solar radiation during rainy season, and the dry wind peculiar to the mountainous region enhanced the transpiration from the leaves and stems cause a deficiency of water in newly growing leaves.
