A New Bacterial Disease on Orchids Dendrobium sp.

Abstract

A new bacterial disease of Dendrobium sp. was observed in the farms of the Nongkham district during the rainy season of 1981. The disease occurred in every orchid farm in this area. The young seedlings and new leaves of mature plants in several varieties of Dendrobium sp. were particularly damaged by the disease. The diseased leaves showed generalized water-soaked rot lesions and wet slimy decay symptoms. But in the dry season, dry symptoms prevailed. At first the wet lesions appeared on the leaves and expanded very rapidly Finally, the infected leaves became yellow or dark brown and dropped off. Nine cultures of the causal bacterium were isolated from the diseased leaves of the seedlings and mature plants. All isolates were pathogenic on Dendrobizlm seedlings causing leaf rot, and the symptoms were identical with those occurring under natural conditions. Examination of the bacteriological characteristics revealed that the causal bacteria were identical with Pseudomonas gladioli which causes soft rot disease of GIndiolus sp., Alliunz sp., iris sp., and Freesia sp. For the determination of species, it was deemed necessary to compare the pathogenicity of the organism with that of a strain of P. gladioli by cross-inoculation on Dendrobium sp. and Gladiolus sp.