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.
Konjak (Amorphophallus konjac) plants showing necrosis in leaflets and stunting of petiole have been found in Gunma Prefecture since around 1960. The causal virus was transmissible by aphids and by mechanical inoculation, but not through corms and cormlets of konjak. The virus was identified to be cucumber mosaic virus (CMV) by immunodiffusion tests. Five CMV isolates obtained from different konjak fields were compared serologically, and three of them were indistinguishable from CMV-Y whereas the other two were identical to CMV-P. All these isolates caused similar symptoms on konjak plants to those observed in the fields. We propose the name of the disease, konjak necrotic stunt disease.
All of the ten isolates of Pseudoperonospora cubensis sampled in greenhouses at Asahi area, Chiba Prefecture, where the effectiveness of the application of phenylamide fungicides for the control of downy mildew of cucumber appeared to have declined since the spring of 1989, were found to be resistant to the fungicides at 100ppm concentration, in assay using the cucumber leaf disc method. Both the preventive and curative effect of the mixtures of phenylamide and mancozeb or copper compounds on downy mildew caused by the resistant isolates were found to decrease in experiments using potted cucumber plants.