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.
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.
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.