Root Tumor of Melon Caused by Actinomycetales

Abstract

In March 1982, pale brownish tumors, the size of which was around 2-15mm were found on the roots of melon (root stock cultivar: Kenkyaku) growing in Kumamoto prefecture, Japan. The symptom resembled to that caused by nematodes. However, nematodes could not be found in the tumor and nematocide was not effective to control the disease. The tumors discolored to brown or black with their development and the plants wilted in the daytime and finally withered. A kind of bacterium was isolated from the surface-unsterilized tumors. The young root of melon artificially inoculated with the isolate produced tumors showing peculiar appearance. The causal pathogen was identified as a species belonging to Actinomycetales from the result of morphological observation. This is the first record of the disease of melon caused by Actinomycetales and the name “root tumor of melon” was proposed.