Abstract
A new bacterial disease of citrus was detected in Yamaguchi Prefecture in 1987. Symptoms appeared on the leaves and flowers of Iyo (Citrus iyo) in the field. In May, the symptoms on leaves were characterized by irregular dark-green, water soaked spots, and defoliation. In June, the lesions enlarged to form round dark-brown spots 5-10mm in diameter with yellow haloes. Symptoms on petals and ovaries consisted of small red spots, and those on pistils of spindly dark-brown spots. The pathogen showed a pathogenicity to lilac, peach, onion, tomato and other 12 plant species. However, the host range was narrow and the virulence was weak in comparison with those of the reference strain, P. syringae pv. syringae (USL-PV). Neither black pit nor blast symptoms were produced on lemon fruits and citrus twigs. The bacteriological characteristics were identical with those of P. syringae pv. syringae (USL-PV). On the basis of these results, we concluded that the disease is caused by a strain of Pseudomonas syringae pv. syringae van HALL 1902 and we propose the disease is designated as “Bacterial brown spot of citrus”.
