The sexual reproductive pattern of Cochliobolus miyabeanus was determined. This fungus is heterothallic and basically hermaphroditic. Two mating types were recognized. Hewever, some long term stock cultures such as KU-13 and IFO-6631 Were unable to form pseudothecia-forming ability. These cultures were fertile when crosses were undertaken with protothecium-forming isolates of an opposite mating group. The phenomenon has not been reported previously in Cochliobolus spp.

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The segregation and distribution patterns of the mating types of Cochliobolus miyabeanus were determined. The segregation ratio of the two types A, B, and C, D was about 1:1 in monoascosporic isolates and 35:49 in monoconidial isolates from field. In field, both mating types were distributed almost equally and moreover co-existence (sympatric distribution) of these types in the same localities or on the same rice plant was demonstrated. Over 60% of both monoconidial and monoascosporic isolates of the fungus were hermaphroditic. The remainder showed a loss of female character(s) in mating tests. Crosses between isolates of H. oryzae from Japan and U.S.A. were attempted. Fertile ascocarps were produced with the correct combinations. The identity of this fungus from both countries was confirmed by the formation of the perfect state.

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Barley yellow mosaic virus (BYMV) and wheat yellow mosaic virus (WYMV) were purified from diseased barley and wheat by clarification with carbon tetrachloride, followed by differential centrifugation and sucrose density gradient centrifugation. Further purification was carried out by isopycnic gradient centrifugation in cesium chloride. The viruses were well dissolved by citrate buffer (0.1M, pH 7.0), but were not dissolved or aggregated by phosphate buffer (0.1M, pH 7.0), borate buffer (0.005M, pH 9.0), acetate buffer (0.1M, pH 5.0), or citrate buffer (0.01M, pH 7.0). The viruses were resistant to carbon tetrachloride, but susceptible to chloroform and butanol. Under sucrose density gradient centrifugation, two zones occurred in the tube. The top zone consisted mainly of short particles, and the bottom zone of short and long particles. Buoyant densities of BYMV and WYMV were 1.294 and 1.281g/cm³, respectively. The ultraviolet absorption spectra of the viruses were typical for nucleoproteins. The characteristic shoulder was present at 290nm in both viruses. The corrected 280:260 ratios of the viruses were 0.88, indicating presence of 5% nucleic acid. The infectivity of the partially purified preparations was rather low. However, an increase in infectivity was obtained with the addition of healthy plant sap. Infectivities of the bottom zone, and mixtures of two zones, were high, but that of the top zone only was low. The viruses purified by isopycnic gradient centrifugation were infectious. Particle length distributions of partially purified preparations had two broad peaks at 200-300nm, and 600nm, whereas three peaks at 275-300nm, and 530-560nm, and 770-820nm were observed in leaf-dip preparations. BYMV and WYMV antisera, both having a homologous titer of 1/640 in a complement fixation test after absorption with normal plant component, were obtained from rabbits which had been immunized with the viruses purified by sucrose density gradient centrifugation. There was antigen common to BYMV, WYMV, and rice necrosis mosaic virus, but each of these also seemed to have its own specific antigen. The antisera did not react with soil-borne wheat mosaic virus.

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Activities of various hydrolytic enzymes in the diseased tissue of rice leaf caused by Xanthomonas oryzae were measured. Their activites were compared with those of the healthy leaf tissue. Moreover the production of enzymes by the pathogenic bacterium was investigated in the cultured solution. Estimated enzymes were as follows: cellulase, invertase, xylanase, phosphatase, β-amylase (α-amylase), pectinase (pectin methylesterase, polygalacturonase), lipase, lecithinase and protease.
1) Activities of examined enzymes increased more in the diseased tissue than in the healthy tissue. On the contrary, polygalacturonase was not activated by the infection.
2) Enzyme activities increased more in the early stage of the infection than in the late stage (8 days after inoculation), except β-amylase. Cellulase alone was activated much more in the late stage.
3) Increased activities of the enzymes seem to be mainly originated from the enzymes produced by the pathogenic bacterium, judging from patterns of pH value-enzyme activity curve and enzyme productivity of tissue and pathogen.
4) There were three peaks in pH value-enzyme activity curve of protease. Of them, pH 8.7 protease-activity increased remarkably by the infection.
5) Influences of metal salts upon the partially purified protease were investigated. Mn", Co" and Fe" promoted the activities of three proteases. Fe'" stimulated only the activity of pH 5.0-protease. Further Hg" inhibited every examined enzyme.
6) Parallel relation was observed between the activity of pH 8.7-protease of the examined seven isolates of the pathogen and their pathogenicity.

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The distribution of silicon in barley leaf epidermal cells infected with Erysiphe graminis hordei was examined using an electron probe microanalyzer. The greatest amount of silicon was detected in the papilla around the haustorial neck. Greater amounts were present in the epidermal cell wall of host cells in the halo region than in the surrounding cell wall region unaffected by the fungus.

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The effects of polyoxin on sensitive and resistant isolates of Alternaria kukuchiana Tanaka were examined at the ultrastructural level. The most remarkable change in polyoxin-treated mycelia of the sensitive isolate was the formation of intrahyphae. The inner region of the cell wall of the original hypha expanded inwards and divided the cytoplasm of the parent hypha into several parts, resulting in the formation of intrahyphae. The cytoplasm of the parent hypha degenerated, whereas that of the intrahypha looked normal. The intrahypha often split the cell wall of the parent hypha and expanded outwards through this split, forming a bulbous structure outside the parent hypha. The content of the bulbous structure appeared normal. The hypha of normal appearance further elongated from the bulbous structure or the intrahypha quite often. The elongation of hyphae from these structures is considered to explain one of the actions that polyoxin acts on this fungus as a fungistat rather than a fungicide. In the resistant isolate, similar mycelial changes were observed but frequency of these changes was much less than in the sensitive one.

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A sieving and floatation technique, using 2% aqueous solution of hydrogen peroxide was developed for extraction of sclerotia of Rhizoctonia solani from soil. Sclerotia were extracted without loss of infectivity. Plant debris particles colonized by the fungus also floated on the solution. Few Rhizoctonia remained in sieved and sedimented soils.

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The most part of conidia and germtubes of Fusarium oxysporum f. sp. raphani placed in natural and crab-shell amended soils are flattened within several days. The observations suggest that the occurrence of flat conidia and germtubes is not affected by any direct action of other soil microorganisms, thus being regarded as a process of autolysis.

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“Susogare” of garden pea in Tokushima prefecture is characterized by yellowing, withering of under leaves and root rot. Aphanomyces euteiches was isolated from diseased pea roots. Peas, inoculated with this fungus, showed same symptoms as observed in field. A. euteiches was detected in 93 of 122 fields tested. It is considered that A. euteiches causes the “Susogare”.

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