Studies on the Root Rot of Tea (Part 1)

The depression of tea plants which principally due to root rot and some of them pro gress to death has been occurring in many tea cultivated areas in Japan. As the first step to reveal the causes of these disorders of tea plant, an evaluation of microbial factor as the causal agent of root rot was made.Isolation frequency of fungi from diseased tea roots (most of them was rootlet) was in order of Fusarium spp., Cylindrocarpon spp., and Pythium-like fungi. Rhizoctonia sp. and Verticillium sp. were also isolated occationally.More than 120 isolates of those fungi were tested their pathogenicity against the cut off tea rootlet in laboratory. Thirteen of the 15 Pythium, 15 of the 17 Cylindrocarpon, 15 of the 42 Fusarium, 4 of the 6 Rhizoctonia and 15 of the 40 isolates of unidentified fungi demonstrated moreor less pathogenicity. Isolates of Pythium, Cylindrocarpon and Fusarium which were found to have the strongest pathogenicities were heavy-innoculated to tea seedlings grown in pot.Each isolate also demonstrated pathogenicity in the experiments and Pythium (P-4) was the strongest.From these results, it was estimated that the microbial factor could be pointed out as a cause of the root rot and might be partially account for the root rots actually occurring in tea fields.Though fungal colony and morphology of mycelium of Pythium-like fungi were characteristics of Pythiutn species, the organ such as zoospore or zoo sporangium was not found and the fungi remained unidentified. MostCylindrocarpon isolates were thought to belong to C. radicicola and a Fusariunt isolate which showed the strongest pathogenicity to F. solani.