In this paper, results of experiments on the relationship between the lodging of rice plants caused by stem rot (causal fungi: Leptosphaeria salvinii Catt. and Helminthosporium sigmoideum Cavara var. irregulare Cralley et Tullis) and disintegration of infected tissues are described. 1. Lodging of diseased plants occurs generally after earing. At this growth stage, in the stem lesion, parenchymatous tissues are disorganized and lignified tissues such as vascular bundles become separated from the epidermal layer. 2. The pectic substances in the middle lamella showed a change in staining reaction, and sometimes were observed to have been digested. Results of viscosity-tests and observations under a polarizing microscope, indicated that the structure of cellulose changed and the specific viscosity decreased. 3. These results indicate that the alteration of the infected tissue was caused by enzymic actions of the pathogenes. 4. Pectic enzymes and cellulases were produced on synthetic medium by the above mentioned fungi, but type of action of enzymes were different between them. More pectic enzymes which dissolve the pectic acid and Cx type cellulase, were secreted by the former than by the latter, while by the latter more pectic enzymes which decompose pectic acid and C1 type cellulase were secreted. 5. Resistance of diseased plants to the lodging was determined in terms of Young modulus of the stem, Young modulus was found closely related with the degree of alteration of cell walls and the separation of lignified tissues in the lesion. 6. From the present experiments, decrease of Young modulus of the stem resulting from chemical and physical changes of the stem tissue infected by the pathogen, was considered to be the main cause of the lodging of diseased rice plants.
In this paper the authors described a virus which was isolated from a wild crucifer plant, Radicula sylvestris Druce and was identified as a strain of tobacco mosaic virus. This virus was named TMV-C. Radicula sylvestris infected with TMV-C showed no symptoms on the leaves. The plant may carry besides TMV-C, other viruses such as cucumber mosaic virus without showing any symptoms. TMV-C was isolated from about 9 per cent of the population of this plant. The virus was highly infectious to turnip and caused distinct mottling on the leaves, but very mild mottling on the leaves of cabbage. Vigna chinensis, Nicotiana glutinosa, N. tabacum var. white Burley, N. rustica, and N. sylvestris showed local necrotic lesions on the inoculated leaves followed by no systemic symptoms. Infected N. tabacum var. Samsun, N. acuminata, and N. debneyi showed necrotic lesions on the inoculated leaves followed by systemic mottling and necrosis. Infected N. alata showed necrotic lesions on the inoculated leaves followed by systemic mottling, and infected N. sanderae showed similar local lesions followed by systemic chlorotic spots. Zinnia plants showed vein clearing, mild mottling, and necrotic patches of the leaves by infection of the virus. N. tabacum var. Ambalema, Phaseolus vulgaris, Vicia fabae, maize, cucumber, and Raphanus sativus var. acantiformis were immune to the virus. TMV-C infection was interfered by the ordinary strain of tobacco mosaic virus in N. tabacum var. Samsun. This virus in the juice of the infected plant was not completely inactivated in ten minutes at 90°C, or by dilution up to 106. The infected sap stored at room temperature or at 4°C gave good infections for thirty days. Under an electronmicroscope, the virus particles show rod shape and about 300mμ long, and are quite alike those of the ordinary strain of tobacco mosaic virus.
The effect of spraying with antiviral chemicals upon the systemic and local infections of plants by several viruses was investigated. When these chemicals were sprayed on TMV-inoculated tobacco plants or TMV plus PVX-inoculated tomato plants 5 or 7 times before and after the inoculation, no decrease in percentage of disease development was found, although the incubation period was somewhat prolonged and the virus content of infected plants, determined b the method of Bancroft and Curtis, was diminished by application of Actidione (2ppm), Dextromycin (100ppm), and Mitomycin (50ppm) about 10∼50 per cent below that of controls. In the case of CMV-inoculated tomato plants, number of infected plants was less by the spraying with Actidione, Dextromycin, and thiouracil. The formation of local lesions produced by the following virus-host combinations, such as TMV-bean, TMV-Nicotiana glutinosa, and PVX-Capsicum annuum, was markedly inhibited by the treatment with Actidone and thiouracil on leaf surface. The rice dwarf disease which is transmitted by the leaf hopper, Nephotettix cincticeps, was unable to be prevented by the spraying. However, the incubation period of this virus prolonged 2 or 3 days by thiouracil or Actidione-spraying. By the soil treatment with thiouracil (100ppm), the occurrence of necrotic disease of tomato plants, which is caused by the combined inoculation with TMV and PVX, was diminished to some extent. From these results, it is concluded that the antiviral substances may be applicable to some virus diseases if proper time and method of application are investigated.
Several salts of ethylene-bis-dithiocarbamate (EDC), such as disodium-(NaEDC), zinc-(ZnEDC), manganese-(MnEDC), and diammonium-ethylene-bis-dithiocarbamate (NH4EDC, ) were applied to tomato seedlings through soil or by spraying on leaves, and their behavior in the plant was examined. Tomato seedlings were grown in soil in 21cm pots, one plant in each pot, and 500ml per single plant of 1/5, 000 solution of ZnEDC or NH4EDC was applied to the soil every day, for seven days. Leaves were then detached, inoculated with Phytophthora infestans, and incubated for five days at 20°C in moist petri dish. Enlargement of lesions was very much retarded by the pretreatment with the chemicals. The leaf juice was found to contain a substance which inhibits the germination of conidia of Cochliobolus miyabeanus. Lower leaves of tomato plants were sprayed with Zn-, Mn-, or NH4EDC while upper leaves were left unsprayed. After 24 hours, the leaves were washed with water and their juices were assayed on C. miyabeanus conidia. Lower leaves contained a similar inhibitory substance, while the upper unsprayed leaves did not. Leaves of tomato plants which had been treated through soil with EDC compounds, especially with NH4EDC, contained a higher amount of non-protein N and total acids, including inorganic acids and some of the TCA members, as compared with leaves of non-treated plants. Cuttings of treated plants were put into 1/15M solution of sodium succinate. After 24 hours, the content of malic acid was determined. The acid content in the treated leaves was much lower than that in the non-treated leaves, suggesting that the malic acid metabolism was stimulated by the treatment. The O2 uptake of the leaf was also stimulated by the same treatment. Dilute NaEDC and MnEDC solutions were stored at room temperature, and change in ultraviolet absorption curve was examined. After one or two days storage, a single peak at 277mμ appeared, indicating the formation of ethylene thiuram monosulphide (ETM) or ethylene thiuram disulphide (ETD). Tomato leaves were sprayed with Na-, Mn-, Zn-, or NH4-EDC. After 4, 24 hours, and 3 days, they were washed with water or with dilute NaOH, and the UV-absorption of the washings were examined. ETM formation was observed after three days. Dilute NH4EDC solution (1/10, 000 at final concentration) was added to the culture of C. miyabeanus, and the UV-absorption of the supernatant solution was examined. ETM was found within 24 hours, while no trace of ETM was detected in the NH4EDC solution without the fungus mycelium.
This paper gives the result of studies on the pectic enzymes of Penicillium digitatum (green mold) and P. italicum (blue mold) which cause storage rot of Satsuma orange. Both these fungi excrete pectin-methylesterase (PE) and polygalacturonase (PG) constitutively in asparagine-glucose medium, and adaptively in asparagine-pectin or orange peel extract medium. PG activity is revealed in the infected orange peel tissues. Optimum pH for PG activity of both fungi lies between 3.6 to 5.5. Despite the strong pathogenicity, protopectinase activities of P. digitatum and of P. italicum are much lower than those of less pathogenic fungi, P. expansum and P. purpurogenum. This fact suggests that pectic enzymes may be one of the important but not the sole factor of the pathogenicity. A question remains unanswered as to what is the factor which plays another important role in the pathogenicity. Both fungi can, not only decompose the pectin, but also utilize the decomposition product as carbon sources in media containing different nitrogen sources. The decomposition products of pectin by culture filtrates are tri-, di-, and D-galacturonic acid, the former two appearing only in an early stage and the last one in a later stage of decomposition.
The causal virus of the seed-borne mosaic disease of adzuki-bean (AzMV) is infectious only to leguminous plants. Among 30 species of Leguminosae, Phaseolus angularis alone shows mosaic, and Astragalus sinicus shows vein-clearing. Canavalia ensiformis, C. gladiata, Phaseolus lunatus, Vigna sesquipedalis and V. sinensis seems to be symptomless carriers. Phaseolus vulgaris var. Master Piece shows symptomless local infection. Thermal inactivation point of the virus lies between 55 and 60°C, and its longevity in vitro is f und to be between 0 and 24 hours at 20°C. Dilution end point lies between 1:100 and 1:1, 000. All the isolates of viruses obtained through seeds of adzuki-bean caused mosaic symptoms on adzuki-bean, but not on asparagus-bean, so far as the present tests concerned. The results of cross immunity tests indicated that the plants infected with Adzuki-bean Mosaic Virus protected the infection of Asparagus-bean Mosaic Virus (ApMV). Consequently the virus is considered to be a strain of Asparagus-bean Mosaic Virus.
In the present paper, the authors report the results of study carried out for a four year period from 1954 to 1957, regarding the effects of tobacco/cucumber mosaic disease to the yield and the quality of tobacco, with special reference to the time of inoculation. The ordinary strain of cucumber mosaic virus (CMV-O) was used for virus inoculum. The test plots were set out as follows: Plot A Inoculation was made to tobacco plants in the seedbed 15 days before transplanting. Plot B Inoculation was made on the day of transplanting. Plot C Inoculation was made 15 days after transplanting. Plot D Inoculation was made 30 days after transplanting. Plot E Inoculation was made 45 days after transplanting. When compared with the untreated check plot, the decreases in yield were 30% in Plot A, 55% in Plot B, 5% in Plot C, 36% in Plot D, and 20% in Plot E. The decreases in quality were 30%, 39%, 41%, 24%, and 0%, respectively. When these decreases are expressed in value per unit acreage, they were 51%, 71%, 74%, 51%, and 18%, respectively. The damage in Plot A was about equal to that in Plot D, the damages in Plot B and Plot C were most severe, while the damage in Plot E was relatively small. It is assumed that the extent of the damage seems to depend on the rise and fall of the virus concentrations in the infected tobaccco and of the symptoms which followed the virus concentrations and at the same time on their relationship with the growth stage of tobacco. The losses in earnings caused by tobacco/cucumber mosaic disease are about equal to those caused by tobacco mosaic disease, but the former affects the yield rather than the quality of tobacco. The damage by tobacco/cucumber mosaic disease may be estimated accurately in terms of the time of infection, if influences of the weather at the site are properly taken into account.