Relationship between Calcium Content in Cuticular Layer of Onion Leaf and Rot of Onion Bulb Caused by Aspergillus niger van Tieghem

Abstract

Onions grown in Ariake state-operated reclamation in Saga Prefecture were found to be more susceptible to the black mold caused by Aspergillus niger van Tieghem than those grown in Shiroishi-machi and Genkai-machi in which onions have been continuously cultivated for more than twenty years. The content of inorganic substances in the cuticular layer of onion leaf was investigated by a transmission electron microscope equipped with an energy dispersive X-ray analyser. Among of inorganic substances, the calcium contents in cuticular layer were constantly lower in the onions grown in the polder land than those grown in traditionally cultivated areas. These results suggest that the calcium in onion tissues may play an important role in the mechanism of resistance to the disease.