In this paper microflora, especially of fungi, on the surface of apparently healthy leaves of rice plants is discussed. The second leaf from the top of variety Nakate Shin-Senbon was used for isolation, and many fungi, such as Candida, Rhodotorula, Penicillium, Alternaria, Aspergillus, and bacteria were isolated. Among them Candida sp. was most frequently isolated. The presence of Candida or other fungi in the conidia suspension of Cochliobolus miyabeanus did not disturb the conidia germination of the latter. However, if the mixed inoculation of Cochliobolus with Candida was performed to rice plants, number of the brown leaf spots decreased, representing about 50 per cent of the control. No microorganism, isolated from leaves of rice plants, inhibited the mycelial growth of C. miyabeanus on agar media.
Only a little has been known about the causal virus of the soil-borne broadbean necrosis of Japan, although the disease has long been investigated. This paper deals with the description of the characteristics of the causal virus, broadbean necrosis virus (BNV), especially its host rage, physical properties, and electron microscopy. BNV is transmitted by plant juice. It causes systemic mild mottling and necrotic symptoms on a few species of Leguminosae, such as broadbean, pea and sweetpea. Local chlorotic lesions or quasi-necrotic ring lesions are formed on serveral varieties of bean, Nicotiana rustica, N. clevelandii, Chenopodium amaranticolor, and Tetragonia expansa. Other plant species tested were not susceptible to BNV. BNV in expressed juice is inactivated at termperatures of 50-55°C in 10 minutes exposure, at dilutions of 10-3 to 10-4, and in 8 to 17 days aging at 20°C. Under the electron microscope, BNV paticles appear to be straight rods about 25mμ in diameter. Two distinct peaks of the distribution of particle length are observed at the lengths of 150 and 250mμ. Only partial protective effect of BNV against tobacco rattle virus was observed in a cross immunity test on sweetpea. From the host range, properties, cross immunity, and particle morophology, it is concluded that BNV is distinct from tobacco rattle virus and also pea early-browing virus, which are infectious to legumes and belong to the TRV-group according to Brandes' classification of elongated viruses.
Miharamycin A, a new antibiotic isolated from cultures of Streptomyces miharaensis nov. sp., has a control effect on rice blast disease. It was also found to have a highly inhibitory effect on plant viruses. This antibiotic inhibited TMV-local lesion formation on detached Nicotiana glutinosa leaves above 90 percent at 2.5μg/ml, and on the intact leaves 85 percent at 5μg/ml, causing no chemical injury on leaves. It also inhibited CMV (Yellow strain)-local lesion formation on intact Nicotiana glutinosa and Chenopodium amaranticolor leaves 80-99 percent at 10μg/ml. Five μg/ml of Miharamycin A almost completely inhibited TMV multiplication in tobacco leaf discs floated for 2 days on its solution. When floated for 8 days, its inhibition value reached 70 percent even at 0.25μg/ml. Moreover, when sprayed on inoculated tobacco plants 4 times, this antibiotic inhibited the rate of tobacco mosaic virus infection by more than 70 percent at 20μg/ml, and prolonged the incubation period more than 20 days compared with control plants. In the case of PVX-Nicotiana glutinosa plants, Miharamycin A inhibited the infection 50 percent at the same concentration. When applied to rice plant by dipping roots with 10μg/ml for 40 hours, or 5μg/ml for 80 hours, this antibiotic inhibited the rice stripe virus infection by 70-80 percent. Miharamycin A caused a chemical iniury on developed leaves at above 10μg/ml, but newly developed leaves were not injured, and the plants grew normally.
Experiments were carried out to understand the inhibition of sporulation of H. oryzae (isolate HA2) by the continuous light in examining the sensitive growth stage in inhibition of sporulation by the irradiation of blue light and the interaction between blue light and near-ultraviolet radiation (BLB). Sporulation of isolate HA2 is dependent upon the length of exposure time rather than the amount of dosage of BLB irradiation. The sporulation process of HA2 seems to be composed of three steps: (1) the initiation of conidiophore formation under BLB irradiation, (2) the maturation of conidiophore progress under darkness and suppressed by blue light and BLB irradiation, and (3) the conidium formation not suppressed by blue light. The blue light inhibits the maturation of conidiophore, and it is most effective when the fungus is exposed to blue light between 4 and 10hr after the termination of inductive BLB irradiation. A small amount of blue light exposure (1, 250erg/cm2/sec) for 10 minutes is enough to suppress the sporulation, when the light is given at the second step of the sporulation process. There seems to exist some interaction between blue light and BLB radiation. This is suggested by the fact that the inhibition of spo-rulation by blue light is counteracted by BLB irradiation. From these results, it is suggested that the inhibition of sporulation by the continuous exposure with BLB is due to the inhibiting action of short wave region of visible light contained in BLB radiation. The less sporulation of the dark period shorter than 8 hr in the alternation of light and dark or a steep decrease in sporulation under the day length longer than 14hr is able to be under stood from the result that the inhibition by blue light of sporulation is most prominent when the blue light is applied between 4 and 10hr after the termination of inductive BLB irradiation.
Plants highly sensitive to sulfur dioxide, namely, rush and buckwheat, were exposed to sulfur dioxide gas of three different concentrations for 30 or 50 days. In any given gas concentration, both plants accumlated sulfur by absorbing sulfur dioxide, with the advance of the exposing period. In rush, the sulfur content at the time of showing injury-tip-burn-symptom of 3% length caused by exposure to 0.26, 0.13, and 0.065ppm gas were about 0.4, 0.8, and 0.9%, respectively. In buckwheat, the sulfur content at the time of appearance of injury-lesion on leaves caused by exposure to 0.26, 0.13, and 0.065ppm gas were about 0.6, 0.75, and 1.2%, respectively. Control plants not treated with gas always maintained about 0.2% sulfur level. Thus, the lower the gas concentration, the higher was the level of sulfur in the plant for liminal appearance of injury-symptom. In the plants which were exposed to sulfur dioxide gas of lower concentration, the sulfur absorbed by the plant seemed to be transformed to less toxic compounds, such as cystine and methionine, but this hypothesis was disproved by the analysis of amino acids in the plants.