It has been known that there are distinct varietal differences of resistance to the soy-bean scab, caused by Sphaceloma glycines Kurata et Kuribayashi. In inoculation tests on 11 varieties, no lesions are found on 4 resistant varieties (Nôrin No. 4, No. 5, Tokachi-nagaha and Kitami-nagaha), but, on 4 moderately resistant (Nôrin No. 2, Nadeshiko No. 1, Akasaya and Iwate No. 1) and susceptible (Nôrin No. 1, Tokachi-hadaka and Ugo-daizu) varieties many lesions are produced. The number of lesions differ at the growth stages of leaves (young, mature and old), the young tissues being more susceptible than the mature or old ones. When the susceptible varieties are inoculated, the causal fungus penetrates into the epidermal cells of leaves, stems and petioles by the infection peg produced from the germ-tube, within 24 hours after inoculation. The penetrated hyphae spreads gradually into the palisade and spongy tissue. Within the infected cells, the decrease of chloroplasts, collapse of nucleus, and the browning and coagulation of cytoplasm are observed. In this case, the incubation period is ordinarily about a week and the sporulation is seen in two weeks after inoculation. On the resistant varieties, when inoculated on young and old leaves, only the epidermal cells are invaded, and the infection is not observed generally in the palisade and spongy tissue, revealing no sign of changes in these tissues. When mature leaves are infected, however, abnormal cell divisions at the palisade tissue under the infected epidermal cells are observed, forming cork cambium layer finally. This layer consists of sclerenchymatous cells of 3-5 layers, and it seems that the mycelium of the causal fungus can not penetrate through the layer. On the moderately resistant varieties, the occurrence of lesions and the resistance reaction of the tissue are influenced by the environmental conditions and nitrogen fertilizer.
In the present paper, the writers reported the change of free amino acid content in rice plants which were cultured in nutrient solution containing following sources of nitrogen: aspartic acid, cystine, glutamic acid, glycine, and (NH4)2SO4 as a control. As shown in Table 3, the content of free amino acid in the rice plants cultured with amino acid surpassed that of the control, and the greatest amount of free amino acid was found in the plants cultured with aspartic acid. Thus the plants may be arranged in the following decreasing order of amino acid content: plants cultured with aspartic acid>glutamic acid >glycine>cystine>(NH4)2SO4 (control). Similar to the results reported in the previous paper, the infection of the causal fungus to the rice plants resulted the decreased of the free amino acid content in leaves, especially of the dibasic amino acid when measured 6 days after the inoculation. There was no significant difference between the plants cultured with amino acid and the control with respect to the number of spots that appeared after inoculation. However, a correlation was found between the amino acid content in leaves and the length of spots which was measured under a magnifying glass (×20). The mean length of spots became shorter with the same descending order as the amino acid content of the leaves does. Accordingly, within the limits of our observations, it may be concluded that the more the content of dibasic amino acids is provided to the plants, the more the spotted area is apt to elongate, and that there exists some correlation between the susceptibility of rice plants to Helminthosporium blight and their amino acid content.
Some oxidizing enzymes of Oryza sativa (rice plant), Cochliobolus miyabeanus, and Piricularia oryzae were investigated. (1) Presence of cytochrome oxidase was suggested in O. sativa, C. miyabeanus, and P. oryzae from the fact that the oxygen uptake was increased by addition of cytocrome-c into the hydroquinone-enzyme system, or into the p-phenylenediamine-enzyme system. High ascorbic acid oxidase activity was also found. (2) High polyphenol oxidase activity was found in C. miyabeanus and various plant polyphenols were oxidized by the same enzyme. The pH optimum of the enzyme was found to be 8.0. The enzyme was inhibited by diethyldithiocarbamate or KCN. However, polyphenol oxidase activity was very low in O. sativa and P. oryzae. (3) Growth of C. miyabeanus was inhibited and brown pigmentation was observed when cultured on the media containing various polyphenols, namely chlorogenic acid, crude polyphenol mixture extracted from rice plant, and so on. (4) From the above results, polyphenol oxidase of the causal fungus seemed to play an important role on the appearance of the symptom, “brown spot formation”, of leaf blight disease in the rice plant.
(1) Polysaccharide, nitrite, and ethanol, those are responsible for a toxicity to host plants, were detected in the cultural filtrate of Fusarium oxysporum f. niveum, the causal fungus of watermelon wilt disease, in addition to the previously reported metabolic products; phytonivein, fusaric acid, and depolymerase. Polysacchaide was identified as heteropolysaccharide having no glucose and caused wilting of host plants, whereas nitrite and ethanol induced leaf necrosis and epinasty, respectively. However, the fungus did not produce these three substances in the cultural solution so sufficient amount as to explain the importance of the substances for disease development. (2) The continuous production of the toxins during the germination of conidia were determined and were presented in Figure 4. Depolymerase and cellulase activities were recognized as soon as the conidial germination. Ethanol was produced after the slight elongation of germ-tube, thereafter fusaric acid and phytonivein were quantitatively detected. The amount of the toxins produced in vitro per one spore was also estimated. The above in vitro experimental results may give a convenient datum to understand the biochemical mechanism of fungal invasion into host cells. Because, the secretions of depolymerase and cellulase, causing break down of host cell walls, happen at the same time with the spore germination, and nextly secretions of toxins, toxic to living cell, begin. But present thinking suggests that the pathogenesis in generally may be responsible for establishing the hyphal invasion into host cell rather than for the strength of the toxin production, and the actions of the toxins are to be looked for the situation on promoting the disease development, the systemic wilting symptoms.
(1) Several antifungal antibiotics were studied in relation to translocation in broad bean plants. The middle leaves of broad bean plant were coated with paste containing the antibiotics to be tested. The paste was composed of 30 per cent petrolatum liquidum, 50 per cent petrolatum album, 10 per cent glycerin and 10 per cent antibiotic. The leaves except the treated leaf, stems, and roots were collected 24 and 72 hours after the treatment. The collected samples were frozen, thawed, and then homogenized with the following solvents. Antimycin A, Blastmycin, Actidione and Phenyl mercuric acetate were extracted with methanol, Humidin with 60 per cent acetone aqueous solution, Blasticidin with the buffer solution of pH 5.0 and Eurocidin with the pH 8.0 aqueous solution. The extracts were assayed for their antibotic activities by the paper disc method or the cup method using the agar plates seeded with Piricularia oryzae. Blasticidin and Eurocidin were assayed by the cup method, the others by the paper disc method. Antimycin A, Blasticidin and Blasmycin were found to be translocated from the treated leaf both upward to the younger leaves and stems, and downward to the older leaves and stems; also in very small amounts to the roots. The leaves or stems above and below the treated leaf were found to contain 0.1-0.5mcg/g of Antimycin A, 0.2-1.2mcg/g of Blastmycin, or 1.4-2.3 mcg/g of Blasticidin. Actidione, Humidin, Eurocidin, and Phenyl mercuric acetate did not move out of the treated leaf in any detectable amount. (2) Stability of the translocated antibiotics in the leaves and stems was studied by greenhouse experiments. The treated leaf was cut off one day after the treatment. The antibiotics were found to have been distributed throughout all parts of the bean plant until that time. The plants were kept in the greenhouse, and the antibiotic activities in the untreated leaves and stems were assayed four and seven days after the treatment. With Blasticidin, less than one third of the original activity remained after 4 days, but no activity after 7 days. Activity of Antimycin A or Blastmycin also decreased gradually, but some activity was still detectable after 7 days. (3) Some additional experiments were done using the rice seedlings. When the first internode of the seedlings was coated with paste containing Antimycin A, Blastmycin, or Blasticidin, the antibiotics were found to be translocated to the upper stems and leaves, also down to the roots. The amounts of antibiotics detected in the untreated parts of the seedling were almost the same as those in the case of bean plants.
An attempt was made to show the inhibitory effect of substances secreted by aphids on feeding plants, upon the infectivity of tobacco mosaic virus (TMV). Pressed juice of tobacco plants affected by TMV, was mixed with pressed sap from Japanese radish, turnip or tobacco, on which a number of aphid individuals belonging to Myzus persicae and Rhopalosiphum pseudobrassicae, had been fed for 24 hours. The virus juice was tested for infectivity by local lesion method using Nicotiana glutinosa. The juice produced local lesions on the half leaves of N. glutinosa far less in number than the control, viz., the virus juice mixed with sap from aphid free plants. When pressed sap from radish infected by radish mosaic virus, was mixed with juice of aphid-infested plants and inoculated immediately to radish seedlings, however, no inhibitory effect upon the virus was observed.
This paper deals with the wilt of Solanum melongena and its causal fungus Fusarium sp. The Morphological and cultural characters of this fungus agree with the description of F. oxysporum (Schl.) Snyder et Hansen. This fungus causes a vascular wilt of Solanum melongena, but is not pathogenic on the other plants of Solonaceae, e.g. Lycopersicon esculentum, Nicotiana tabacum, Solanum tuberosum and Capsicum annuum. On the other hand, the various forms of F. oxysporum, that is, f. lycopersici, f. nicotianae, f. batatas, f. callistephi, f. conglutinans, f. lini, f. melonis, f. narcissi, f. niveum, f. pini, f. pisi, f. spinaciae, f. vasinfectum, f. cucumerinum, and the strains of F. oxysporum isolated from the root of wilted potato or the tuber of potato, etc. proved to be non-pathogenic on S. melongena. From these results, the writers propose the following name for the fungus. Fusarium oxysporum (Schl) Snyder et Hansen, f. melongenae Matuo et Ishigami, nom. nov. Hab. in vivis Solani melongeni, cetera ut in typo. The type culture is deposited in Fac. Text. Seric. Shinshu Univ., Ueda, Japan, which was isolated from Solanum melongena suffered from a vascular wilt disease.
Effects of orange fruit contents on the growth of Penicillium digitatum (Green mold of citrus) and P. italicum (Blue mold of citrus) were studied. The growth of P. digitatum was more vigorous on the media of smashed rind tissue rather than on juice agar, while P. italicum showed similar growth on both media. The growth of P. digitatum was stimulated on synthetic agar media containing fruit rind extracts. It is indicated that the growth of P. digitatum is stimulated by the contents of fruit rind. The growth stimulating substance or substances are soluble in water, 80% methanol or 80% acetone, but not in ether. Desiccation or pasteurization of the rind has no influence on the stimulative action.
It is believed that barley yellow-mosaic virus (BYMV) is a distinct virus found only in Japan and that it differs from other soil-borne viruses of cereal crops. BYMV does not attack wheat and rye, it is not transmitted by insects and is not seed-borne. The writer has investigated continuously the mode of the disease and properties of BYMV. The experimental results obtained are summarized as follows: (1) In the variety tests of barley sown in BYMV-infested soil, most foreign varieties tested were infected with the virus as well as domestic varieties, with different infection rates or with varied grades of severity of symptoms. In these tests, it was shown that hulled varieties were more susceptible to the virus than hull-less varieties, particularly two-row barley varieties developed severe symptoms. It was observed in the tests, moreover, that the environmental conditions exerted effects upon the infection and expression of symptoms. (2) Among the tested plants of wild species of Hordeum, H. spontaneum (C.I. 4142) and H. agriocrithon plants were found susceptible, and intracellular inclusions (X-bodies) were recognized in the cells of the diseased plants but all the symptoms shown were rather mild. (3) In the linkage testers of barley plants, no plant belonging to the linkage groups I or VI was infected with BYMV. But the other plants belonging to the groups II-V and VII were susceptible to the virus with rather severe symptoms. (4) When pre-germinated seeds, which had already developed 2 or 3 roots, were planted in virus-infested soil out of doors, the infection rate became greater than in the cases of the planting of seeds, which were presoaked but had not yet developed roots. However, the infection rate of the former was not much higher than the latter as shown in the previously reported results, i.e., 2-3 times as high in glass-house tests. It was found, eventually, that the differences between the infection rates of the former and of the latter became greater when the tested plants were kept under unfavorable conditions for the occurrence of infection with the virus. (5) In the test of stability of BYMV, leaves of barley affected with the virus were clipped into 2-3cm pieces; they were put into a tight bottle containing calcium chloride crystals in the bottom. Then the bottle was placed and stored in an electric household refrigerator which was regulated at 0-2°C for the first one month and at 5-10°C for about two years. After that length of time, inoculation test was made by wiping water extracts of the dried tissues on leaves of seedlings. The infection rate of the dried tissues showed one-third value of the rate in the case when fresh diseased leaves were used as inoculum.