Strawberry root rot was first recorded in a small area in the suburbs of Shizuoka city in 1949, where strawberries are usually grown on paddy fields after rice plants have been harvested and the flooding water has been drained off. Since then this disease has spread in the strawberry growing areas in Shizuoka Prefecture. The symptoms were always accompanied by red stele which is characteristic to the Phytophthora infection. When the roots showing the red stele symptom were immersed in water, the pear-shaped sporangia characteristic to Phytophthora appeared abundantly on the root surface. The root rot disease of strawberry occurring in Osaka and Hyogo Prefectures was also accompanied by the red stele symptom. Abundant sporangia of Phytophthora were always detected from these diseased roots. The results indicate that the root rot disease is identical with that occurring in Shizuoka Prefecture. Phytophthora sp., Fusarium oxysporum, Pythium spp., Rhizoctonia sp., and other unidentified fungi were isolated from the diseased roots. Inoculation experiments showed that only Phytophthora sp. was responsible for the unique red stele symptom. The Phytophthora sp. was identified as Phytophthora fragariae Hickman from the physiological and morphological characteristics.
For the purpose of surveying damage by late infection of citrus melanose, the author carried out inoculation experiments upon Satsuma mandarin (Citrus unshu) fruits with the causal fungus, Diaporthe citri (Faw.) Wolf, during the period from September to November. The method of experiment was as follows: two kinds of infected twigs, as inoculum, were hung near above fruits on trees for several days. The one was the twigs artificially inoculated with the causal fungus in test tubes, while the other was the dead twigs gathered from an old tree of Natsudaidai (Citrus natsudaidai) in the field. The spore horns of the fungus had been abundantly produced on those twigs. Fruits were covered with paraffin paper bags in order to protect them from natural infection. Surveys on late infection of the disease both in the fields and in packing houses were carried out at three places in Hiroshima prefecture. Results of these experiments and surveys are summarized as follows: 1. By means of inoculation using infected twigs, the symptoms of melanose made their appearance on Satsuma mandarin fruits even in early November. The occurrence of the disease seemed to depend primarily on quantity of rain fall, but the ages of fruit were proved to be of a rather minor factor for the infection. 2. Two types of symptoms appeared on Satsuma mandarin fruits. The one, caused by inoculation before the end of August, was characterized by blackish brown protrusive pimples by slight whitish border. The other, caused by inoculation after September, showed blackish surrounded brown pimples surrounded by greenish halo. 3. The results of survey in the field demonstrated that damage caused by late infection are as much as those by earlier infection in summer.
Phage-typing of the bacterial leaf blight and bacterial leaf streak pathogens was carried out on isolates obtained from the Philippines, Thailand and Indonesia. A comparison of the lysotypes of the blight pathogen in Japan and the Philippines was made using seven X. oryzae phages. X. oryzae phages were specific to X. oryzae, but X. translucens phages Sp3 and Sp6 lysed certain isolates of several xanthomonads in addition to X. translucens f. sp. oryzae. The streak pathogen was differentiated into 16 lysotypes and the blight pathogen into 15. X. oryzae phage Bp1, distributed widely in the Philippines (Luzon area), was identical to the phage Op2 of Japan in the host range, but other Philippine phages differed from those obtained from Japan.
A biochemical plant pathology seminar was held at Zyozankei, Hokkaido on August 18-20, 1965. The following progress reports were presented at this meeting. 1. Oku, H. (Sankyo Pharmacological Institute, Shinagawa, Tokyo): The physiological and chemical properties of the pathogen and their contribution to the formation of Helminthosporium leaf spot of rice. 2. Tani, T. (Faculty of Agriculture, Kagawa University, Miki, Kagawa): Studies on the pathological physiology of anthracnose of Japanese persimmon, with special reference to the role of pectic enzymes to the symptom development of the fruit. 3. Nishimura, S., Scheffer, R. P., and Nelson, R. R. (Faculty of Agriculture, Tottori University, Tottori; Michigan State University, East Lansing; North Carolina State College, Raleigh): The metabolism of victoxinine produced by the genus of Helminthosporium. 4. Otsuka, K. (Faculty of Education, Niigata University, Niigata): Biochemical studies on the physiological races of Piricularia oryzae. 5. Tomiyama, K., Sakai, R., Sakuma, T., and Takemori, T. (Hokkaido National Agricultural Experiment Station, Sapporo): The metabolism of phenolic compounds found in the tissues adjacent to the resistant lesions and their role in the resistance. 6. Toyoda, S. (the late) and Suzuki, N. (National Institute of Agricultural Science, Tokyo): The carbon metabolism of black spot fungus of pear and the mode of action of copper fungicides against the fungus. 7. Asahi, T., Verleur, J. D., Honda, A., and Uritani, I. (Faculty of Agriculture, Nagoya University, Anjo; Free University, Amsterdam): Biochemical studies on the mitochondria obtained from injured and diseased plant tissues. 8. Ouchi, S., Shishiyama, Z., and Akai, S. (Faculty of Agriculture, Kyoto University, Kyoto): The mechanism of inactivation of plant virus by ultraviolet ray. 9. Takahashi, T. and Hirai, T. (Faculty of Agriculture, Nagoya University, Anjo): Mitochondrial activity of tobacco leaves infected with tobacco mosaic virus. The discussion was mainly focused on the toxic and enzymatic substances produced by fungi and their action within host plant tissues and on the phenolic compounds and polyphenol oxidases which are found around the infected tissues. Special mention was also made on the mitochondria in potato tubers and sweet potato roots as well as in tobacco leaves, with reference to the oxidative activities.