Investigations on“Abnormal defoliation”of Satsuma orange in Honshu and Shikoku districts

Abstract

This study was carried out to prove whether the symptoms of so-called“Abnormal defoliation”in Honshu and Shikoku districts are the same as that in Kyushu district or not.In our observation, it was recognized that the symptoms were the same among these districts.But in Honshu and Shikoku, the symptoms of “Abnormal defoliation”were confused with that of greasy spot, phoma rot or defoliation by cold damages.The Satsuma orange tree which showed the symptoms of“Abnormal defoliation”contained more than 100ppm of manganese in its leaves, as observed in Kyushu.High content of manganese in the leaves may be caused by the increase of water soluble manganese in the soil. It was observed that the water soluble manganese content in the soil is closely related to the soil pH.It was not possible, however, to clarify the relationship between the soil acidity or water soluble manganese content in the soil and the occurence of“Abnormal defoliation”in the present investigation. It would be suggested that the soil acidity or water soluble manganese content in the soil observed was not the same as that at the time of the occurrence of“Abnormal defoliation”.