Several isolates of Pseudomonas lachrymans showing resistance against dihydrostreptomycin (DHSM) were obtained from naturally infected cucumber leaves. Cellfree systems prepared from these isolates including N-7641 were able to inactivate DHSM, in the presence of disodium adenosine triphosphate. These enzymically inactivated DHSM were regenerated by alkaline phosphatase treatment, and not by phosphodiesterase. Inactivated DHSM was isolated in crystalline form and its chemical structure was elucidated by means of proton magnetic resonance etc. It was found that the hydroxyl group at C-3 position of the N-methyl-L-glucosamine moiety in DHSM was enzymically phosphorylated. From these results, it was concluded that ATP: aminoglycoside 3"-phosphotransferase participated in DHSM-resistance of Pseudomonas lachrymans N-7641.

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The surface structure of local lesions on cowpea leaves infected by cucumber mosaic virus was observed with a scanning electron microscope. When the leaf surface was rubbed with inoculum virus and Carborundum, a variety of injuries were produced on the surface. The local lesion was composed of a few injured cells and 20-30 surrounding uninjured cells. The injured cell had a wound hole of 30-150nm diameter on the cell surface having a lump-like structure. All of the cells within the local lesion showed shrinkage, and the lesion area was concave and sharply distinguishable from the surrounding areas. On the other hand, no lesion was developed from seriously wounded cells. These observations suggested that virus might enter through the micro-holes at the lump-like structure of the injured cells, and that the surrounding cells might become infected by infectious materials synthesized in the initially infected cells, followed by the cell shrinkage and the lesion formation.

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Foliage blight of sugar beets in Hokkaido is mainly caused by the anastomosis group AG 2-2 of Thanatephorus cucumeris (Rhizoctonia solani). The leaves of sugar beets (cultivar Monohope) were inoculated with basidiospores of isolate Rh-509 artificially produced on the soil surface. The germinated basidiospore penetrated the epidermal cell directly, with the formation of an appressorium. Invading hyphae produced a stroma-like body within the epidermal cell or the upper layer of the mesophyll. After that, hyphae grew out from this body radially and caused small, 1mm in diameter, circular lesions, called primary lesions. With further keeping of the diseased plant in the moist chamber, hyphae growing out from the primary lesions developed and ramified on the leaf surface, and the hyphal tips entered the leaf through the stomata, causing secondary lesions which were scattered or enlarged all over the leaf surface. From observation of naturally infected sugar beet leaves in the fields, stroma-like bodies were detected, but not in the inoculation with mycelia.

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The root hair infection with Plasmodiophora brassicae Wor. was the most frequent in the 2-3cm part of the tap root below the hypocotyle of Chinese cabbage (cv. Kinshyo-hakusai) grown in the soil infested with 10⁶ spores/g dry soil at 25C for 12 days. Clearly differentiated zoosporangia were found at first in the infected root hair cells in 7-day-old seedlings, followed by the completely evacuated zoosporangial clusters in 8-day-old ones. No root hair infection was found at the lowest spore density of 10 spores/g dry soil, neverthless severely clubbed roots were formed. Although the frequencies of infected root hairs, clubbed plants, and the disease index were increased with the spore density, the spore density correlated only with the disease index (r=0.82^**). The minimum spore density required to produce clubbed roots was more than 3.55 spores/g dry soil. There was no correlation between the root hair infection and the disease index. In Chinese cabbage seedlings used in this study, it seems that a few infected root hairs may be associated with subsequent club formation.

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Phytophthora rot of pumpkins (Cucurbita maxima, cultivar Ebisu) was observed in Ikeda and Shibetsu, Hokkaido in 1974 and 1975 respectively. Based on morphological, physiological, and pathological characters, the causal fungi were identified as Phytophthora capsici Leonian. All 50 single zoospore cultures of Ikeda isolate behaved as A¹ compatibility type. Twenty-eight of 30 single zoospore isolates of Shibetsu fungus, soon after isolation, produced no oospore and behaved as A² type. But after they were stocked for 18 months (transferred at intervals of 5-6 months), abundant oospores were formed, usuaIly in sector(s) or around initial inoculum when subcultured on V-8 agar plates, incubated at 23C in the dark for 10 days. The other two isolates usually produced oospores in segment(s); one, 15 days after isolation, another, after stocked for 28 months. Sterile areas acted as A² compatibility type.

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Lazy-Ginga, la-isogenic line of Ginga, proved that Rb₁ of Sensho linked with la had not been introduced to Ginga. Absence of Rb₁ caused a significant decline of blast resistance to Ginga. From comparison of derivatives with their common parent, Sensho, it was ascertained that the present decline commenced in the early stage of the breeding program.
The two blast resistance genes which controlled the moderate resistance of Ginga were assumed to be multiple alleles of the two ones other than Rb₁ of Sensho.

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The developing process of Plasmodiophora brassicae from the very young plasmodium to the fully matured resting spore was examined by using a scanning electron microscope on the infected cortical cells of turnip and Chinese cabbage. In the early stage of infection, the initial plasmodia in an infected cell were observed as spherical bodies of smooth surfaces with or without strand-like materials and ranged from 3 to 5μm in diameter or as a small cluster mass. The plasmodia developed rapidly. The cut surface of young plasmodia indicated that these developed into a large sponge-like structure. In some cases, the plasmodia consisted of spherical bodies. In a club-cut surface, young plasmodia and vegetative plasmodium were found in the two contiguous cells, respectively. With progressive growth of a plasmodium, a mature resting spore mass was seen in a cell and young plasmodia were noted in its contiguous cell. Young plasmodium or vegetative plasmodium and a resting spore mass were found together in a cell. Immature resting spores were observed to have filamentous connecting materials, while mature spores exhibited spines on their surfaces. At 45-60 days after sowing, the resting spores in an infected cell of club sampled perfectly matured and the cell was filled by innumerable spores. The spore mass did not appear to have an enveloping membrane. In paraffin sections of club tissue, the cell wall of the resting spore was clearly seen.

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Hop stunt disease (HSD) is prevalent in hop gardens in Japan since 1952. The cone yield of the diseased hop plants (Humulus lupulus cv. Kirin II) was reduced to at most a half of that of HSD-free hop plants. The alpha-acid content of the diseased cones was also decreased from one-third to one-half of that of HSD-free cones. HSD has been long suspected to be a virus disease according to graft and sap transmission, although no virus particle was detected. The only known hosts of HSD are H. lupulus and H. japonicus which have long incubation periods of 2-3 years and more than 3 months, respectively after inoculation. Thus studies on the properties of HSD agent have been extremely limited by lack of suitable indicator plants.
Cucumis sativus, C. melo, C. melo var. conomon, Lagenaria siceraria var. clavata, gourda and microcarpa, Luffa cylindrica and Lycopersicon esculentum were confirmed as the host plants of HSD agent. Except L. esculentum plant which was recognized as a symptomless carrier, all the other infected plants showed mainly stunting one month after inoculation. Twenty-one cultivars of cucumber plants inoculated were all infected. The symptoms of cucumber plants appeared earlier at about 33C than at about 21C. HSD agent was not transmitted by Myzus persicae. Virus particles were not detected from diseased cucumber plants by dip preparations and ultra-thin sections.
It is interesting to note that the symptoms on infected cucumber plants and the host range of HSD agent are quite similar to those of cucumber pale fruit disease in Europe.

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The occurrence in oat leaves of non-antifungal steroids, avenacosides (Avd) A and B, was confirmed by chemical and physical analysis for primary leaves of oat cultivar Shokan 1. Enzymatic conversion of Avds A and B into antifungal steroids 26-desglucoavenacosides (26-DGA) A and B, respectively, was also demonstrated. The enzyme was active to β-glucoside linkage at C-26 of Avds and was inactive to that of sugar moiety at C-3 of Avds and 26-DGAs. No split of glycoside linkage of flavonoids present in oat leaves as well as p-nitro-β-d-glucoside was detected. The activity was maximum at pH 6.0, heat labile and inhibited by p-chloromercuric benzoate but not by gluconolactone. In leaves injured by cutting, conversion of Avds into 26-DGAs occurred within 5min and the degree of conversion was correlated with the increased antifungal activity of steroid fraction from hot methanol extracts of leaves, as measured by the growth of uredospores of Puccinia coronata avenae. It was suggested that the activation system of Avds to antifungal forms in association with the activation of a specific β-glucosidase was involved in the injured response of oat leaves.

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Cortex tissues of one-year-old shoots of mulberry cultivar Ichinose, were inoculated with spore suspension or myceria of Fusarium solani f. sp. mori. The shoots were incubated in a moist case for various periods. Ten cortex disks 7mm in diameter or 0.2g of cortex tissues were immersed in 1ml of acetone for 3hr. Antimicrobial activity (AA) of the acetone extracts was examined with 1) hole slide- 2) cup- 3) TLC- 4) Plate- method using spores of Bipolaris leersiae. The extracts from infected tissues of summer and winter shoots showed AA. But AA was not detected in the extracts from non-infected cortices. Heated (90C, 10min) spores could not induce the AA. It is more necessary than 10² spores per cm² of cortex surface to induce the AA. The AA was found in the extracts from cortices of shoots which were incubated at temperature ranging from 5 to 30C after inoculation of the spore suspension. Browning occurred in the infected tissues of cortices at higher temperature than 20C and AA was recognized only in the extracts of browned parts. Although browning of tissues was not observed so clearly at 5 and 10C, AA was detected in the extracts from all of the infected tissues of cortices. AA was found in the extracts from both summer and winter shoots, but little AA could be detected in upper part of new shoots in June. Growth of pathogenic fungi and bacteria of mulberry or silkworm was inhibited by the extracts from corticies inoculated with F. solani f. sp. mori. The AA was induced in the cortices by the treatments with culture filtrates of 7 plant pathogenic fungi. Antimicrobial compounds (AC) were extracted from cortex tissues inoculated with F. solani f. sp. mori with methanol, acetone, ethyl acetate and ethyl ether, but could not be extracted with water, n-hexane, carbon tetracloride. The AC were stable for 1hr at 120C or more than 6 months at 20C. The AC were dialyzable. Rf values of the AC on the cilica gel G thin layer chromatograhy developed with ethyl ether were 0.20 and 0.63. From these results, it was concluded that the AC were phytoalexins of mulberry. Chemical stractures of the AC of Rf value 0.63 were determined and these new compounds were named as moracin A and B by M. Takasugi et al.

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The patterns of sclerotial development in Botrytis cinerea were studied under controlled enviromental conditions capable of inducing sclerotial formation. Two types of sclerotial development were distinguished. Terminal type of sclerotia was induced by mounting a cover-glass on the tips of vegetative hyphae for a definite period of time. On the other hand, lateral type of sclerotia was induced in a narrow region of the mycelia produced at the beginning of high-temperature treatment by exposing to a temporary high-temperature. Thus, in Botrytis cinerea which has been previously grouped into a former of terminal type of sclerotia, there also exists the lateral type of sclerotial development.

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The investigation was made to elucidate the differences in peroxidase activity between the compatible and incompatible infection of rice leaves with Xanthomonas oryzae. Peroxidase activity, which was measured by a colorimetric method, increased markedly as lesions enlarged in the susceptible leaves, and showed a value 1.6 to 1.8 times higher as compared with that of leaves at an onset of inoculation. In the resistant leaves, on the contrary, the activity increased slightly, and showed a value 1.2 to 1.4 times of initial activity. On the other hand, in the healthy or needle pricked uninoculated leaves very slight increases (1.1 times) occurred within 14 days after the onset of experiment. The activity in the lower aged healthy leaves was higher than that in the upper immature ones. Both the decrease in chlorophyll content and the increase, in peroxidase activity were greater in the susceptible leaves than in the resistant or the healthy ones, then negative correlation between the chlorophyll content and the peroxidase activity was obviously observed. Eight bands of peroxidase isozymes, which were revealed by a polyacrylamide gel disc electrophoresis, were detected from both gels of infected and healthy leaves, but the intensity of staining by benzidine hydrochloride-H₂O₂ was highest in the susceptible leaves, the resistant leaves followed, and the healthy leaves was lowest. These differences in the intensity of staining were marked especially in the three bands among eight ones. These three isozymes were stained much densely in the lower leaves than in the upper leaves. From the above results, it was evident that the peroxidase activity might be increased in the infected susceptible leaves and might not be involved in resistance expression, and that the activity might be increased in the susceptible leaves in accordence with accerelation of senescence in the infected tissues, since qualitative difference was not observed between the healthy and infected leaves.

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L₁₁A, an attenuated tomato strain of TmV which has been efficiently used for the protection of tomato plants against mosaic disease, proved to be inffective for protecting the existing TmV-resistant tomato cultivars having Tm-1 gene, possibly because the strain hardly multiplies in these cultivars, consequently the plants are readily infected by a virurent strain, e.g., CH2. For the purpose of obtaining another attenuated strain enough effective for protecting these cultivars, a new attenuated strain of TmV, L₁₁A237, was isolated by successive passages of L₁₁A through TmV-resistant GCR237 tomato (Tm-1/Tm-1). The new strain, alike L₁₁A, causes no symptoms in tomato and Samsun tobacco, but differs in that it multiplies much faster than L₁₁A in the existing TmV-resistant tomato cultivars (Tm-1/+) and sometimes causes necrotic rings on Xanthi nc in the environment in which L₁₁A causes necrotic spots.
In cross protection tests in resistant tomato cultivars, L₁₁A237 interfered more strongly with the multiplication of CH2, a virulent tomato strain of TmV infective to resistant tomato cultivars (Tm/+), than L₁₁A did.
In the experiment in a plastic greenhouse the inoculation of resistant tomato seedlings (cv. Tanomo, Tm-1/+) by L₁₁A237 resulted the good control of mosaic disease, and an higher yield than the yield of a plot which had not been inoculated with this attenuated virus.
In the plastic greenhouse of a tomato grower the effectiveness of L₁₁A237 and L₁₁A was compared using Tanomo tomato plants. The hundred-times diluted saps of L₁₁A237-and L₁₁A-infected tomato leaves were mixed with 1 per cent 800 mesh carborundum and inoculated to tomato seedlings at the distance of 10cm by working pressure of 5kg per cm² with a motive sprayer. About 10 days later L₁₁A237 and L₁₁A garanteed 67 and 7 per cent infections and tomato plants inoculated showed mosaic symptoms of wild virus by 1 and 25 per cent after 5 months respectively.
These results indicate that L₁₁A237 is very effective for the protection of the ordinary TmV-resistant tomato cultivars (Tm-1/+) from the infection by a virulent strain like CH2.

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N-(3', 5'-dichlorophenyl)-1, 2-dimethylcyclopropane-1, 2-dicarboximide, procymidone (S-7131, Sumilex^(R)) inhibited increase in hyphal cell number of Botrytis cinerea preceding inhibition of increase of hyphal dry weight.
Oxygen consumption of the mycelium was hardly affected. Procymidone curtailed increase in protein, RNA and DNA contents at the rates approximately corresponding to that of inhibition of dry weight increase. The incorporation of ³H-uridine into acid-soluble and acid-insoluble fractions of the cells was more rapidly and strikingly inhibited. The effect on uridine incorporation may be ascribed to disturbance of membrane function for the transport. Procymidone moderately affected the incorporation of ¹⁴C-acetate into total lipids and did not specifically inhibit the synthesis of individual lipid class. The synthesis of the cell wall was stimulated by the treatment of procymidone without marked change in its constituents. Though the primary site of action of procymidone is still obscure, it is supposed that procymidone may act on cytoplasmic membrane and its action must be related to membrane function for the transport and cell wall synthesis.

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In 1976-1977, a Phytophthora stem rot of adzuki-bean (Phaseolus angularis) was discovered in Hokkaido, and the causal fungus was identified as P. vignae Purss. On the stem of adzuki-beans the characteristic lesions with reddish-brown streak appeared, and the affected plants finally wilted and blighted. The pathogen attacked only three cultivars of adzuki-bean and could not invade 14 another plants tested.

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