On the Causal Fungus of the Leaf Spot Disease of Tea Plant

Abstract

The causal fungus of the tea leaf spot disease has been recognized as Phyllosticta theaefolia HARA since 1920, but the inoculation in field using the fungus has not yet been succeeded. On the other hand, in 1939, KUROSAWA reported the tea scab disease which closely resembled to the leaf spot in symptom and was caused by Sphaceloma theae.The author has investigated the causal fungus of the tea leaf spot and the difference between these two diseases for several years.The results are summarized as follows :1. Sphaceloma sp. was isolated frequently from the tea leaf spot lesions as well as Phyllosticta sp. and the tea brown blight fungus.2. According to the inoculation experiments using Phyllosticta sp. and Sphacelonza sp. both in the field and in the laboratory, Sphaceloma sp. only showed distinct pathogenicity on the young leaves and shoots, and the symptom was hardly distinguishable from that of naturally infected leaves.3.The morphological characters of Sphaceloma sp. were as follows : Acervuli develop like hills on the upper and under surfaces of leaves, light greyish brown or colorless and are 20-125X10-25μin size. Conidiophores are one celled and 2.5-17.5μ in length. Conidia develop singly from the tip of conidiophores, elliptical shape, singly celled and having generally two oil spots at the two opposite ends. The size of conidia from cultured fungiis(isolate S-2) is 4.7-7.3×2.3-5μ, mean 5.8-2.8μ. There was no difference between Sphaceloma sp. and S. theae. KUROSAWA in the morphological characters.4. Because of the leaf spot disease was quite identical in symptom and causal fungus with Kurosawa's scab disease, the author concluded that the leaf spot was synonymous with the scab.