The present investigation was undertaken to evaluate the effectiveness of 23 halogenophenylpyrazolone, 16 halogenophenylhydrazine and 12 halogenophenylacetylhydrazine derivatives on sheath blight of rice, and also the effectiveness of some of them on rice blast, bacterial leaf blight of rice, cucumber anthracnose and soft rot of chinese cabbage. Halogenophenylpyrazolone, halogenophenylhydrazine and halogenophenylacetylhydrazine derivatives substituted at 1-position with 4-halogenophenyl group were effective and the structural modifications of these compounds had intimate relation with their controlling action against sheath blight of rice. It was assumed from the results of this test that halogenophenylpyrazolone derivatives would be decomposed to some hydrazine derivatives upon rice plant and give good controlling effect. From the results of the seedling bed test in greenhouse, three halogenophenylpyrazolone, five halogenophenylhydrazine and three halogenophenylacetylhydrazine derivatives showed good controlling effect upon rice blast, especially the effectiveness of both 1-(3, 4-dichlorophenyl)-2-acetylhydrazine and 4-chlorophenylhydrazine·formate were estimated very highly. Ten halogenophenylpyrazolone and four halogenophenylacetylhydrazine derivatives gave good protective effect on cucumber anthracnose, but these compounds were not effective on bacterial leaf blight of rice and soft rot of chinese cabbage.
A potato plant cell can survive for longer than two days after the infection by a compatible race of Phytophthora infestans. On the contrary, it dies hypersensitively within about 30 minutes after infection by an incompatible race in this experimental condition. When a potato plant cell, which has been infected by a compatible race of Phytophthora infestans 15-20 hours previously, was reinoculated with an incompatible race, no cell-death caused by the hypersensitive reaction to the latter occurred at least within four hours. However, several hours after the primary infection by the compatible race, occurrence of the hypersensitive death of the host cell caused by the secondary infection by the incompatible race was only slightly delayed. The control cell treated in the same way, except the previous infection by the compatible race, died within ten to twenty minutes after the infection by the incompatible race. It is concluded, therefore, that the potato plant cells gradually lose their hypersensitivity to the incompatible race after the infection by the compatible race.
In the previous papers we reported on the isolation of piricularin and picolinic acid, the toxins of Piricularia orizae, from the culture broth of the fungus and the rice plant, severly infected with blast disease, and then on the biochemical observations of the effects of these toxins to the rice plant. To determine whether or not piricularin takes part in the blast fungal infection, we investigated the effect of a piricularin-detoxifying substance on the resistance of rice tissue to this infection. As a piricularin-detoxifying substance we chose ferulic acid (4-hydroxy-3-methoxycinnamic acid) which is a minor ingredient of polyphenols of rice plant, since it is easy to obtain by synthesis and it has not an anti-blastfungal activity. The experimental results demonstrated that the application of ferulic acid to the rice plant causes an increase in the tissue-resistance to the blast-fungal infection. The following facts support the view that the increase in the resistance to the infection of rice plants treated with ferulic acid depends upon the piricularin-detoxification: (a) Neither ferulic acid itself nor its oxidized product by oxidase exhibits any anti-blastfungal activity at 1/5, 000 dilution with the pH level of rice juice. (b) Not only ferulic acid but its oxidized product by oxidase also has a piricularin-detoxifying ability. (c) The juice pressed from the rice plant applied with ferulic acid also possesses a piricularin-detoxifying ability, exhibiting no inhibitory effect on the germination and growth of blast fungal spores. (d) The application of ferulic acid causes a respiration-rise of the rice plant, but this respiration-rise does not couple with oxidative phosphorylation which is to be related to the resistant reaction of the host tissue against the infection. The above mentioned observations lead to the conclusion that piricularin would play an important role in the blast-fungal infection together with picolinic acid suppressing the resistant reaction, i.e. the hypersensitive reaction, of the host tissue to the infection.
Myzus persicae Sulz. fed on potato leaf roll-infected Physalis floridana Rydb. for 30 and 60 minutes were not able to infect healthy P. floridana seedlings within 3 hours after leaving the source plants. Following feedings of 10 minutes, 1, 3, and 24 hours on infected P. floridana, the aphids were singly transferred to healthy P. floridana at 24 hour intervals for 5 days, and 0, 2.6, 12.5, and 50.0 per cent infections occurred between 24-48 hours after leaving the source plants, respectively (Table 1). The aphid vectors reared on infected Datura stramonium L. were able to transmit the virus to P. floridana within 5 minutes. A mild strain of potato leaf roll virus was more readily transmitted by the aphids than a severe strain (Table 2 and Fig. 1). Adults and nymphs of the aphid reared on Chinese cabbage were allowed to feed on infected P. floridana for 2 days, and then were serially transferred to healthy P. flaridana daily, one aphid per plant, until they died. The nymphs were more efficient vector than the adults. After the both forms of the aphid left the source plant, there was a tendency that their ability to transmit the virus gradually increased and then decreased (Fig. 2). Following acquisition feeding times of 1, 3, and 6 hours on infected P. floridana, the aphids were serially transferred to healthy P. floridana daily, one aphid per plant, until they died. As acquisition feeding times were lengthened, the rate of transmission increased and retention of inoculative ability was prolonged. However, independent of the length of the acquisition feeding times, the efficiency of transmission attained a maximum within a certain time after leaving the source plant and then declined (Fig. 3 and 4). The ability to transmit the virus was found to vary considerably with individual aphids.
The dish technique of Schütte (1956) was modified to study the formation of sclerotia of Rhizoctonia solani. First, a small dish containing 7.5ml of agar medium is placed at the center of a Petri dish, after which 15ml of agar medium is poured into the remaining space. The contents of agar media in both dishes are different, i.e. Czapek's agar lacking sugar but containing all other nutrients, and distilled water agar containing only carbohydrate. The fungus, inoculated at the center of the small dish, develops a colony, and then sclerotia are formed on the agar medium deficient in carbohydrate, irrespective of the site in dish, while few sclerotia are formed on the medium containing carbon sources. In other words, sclerotia of the fungus are formed by utilizing carbohydrate, which is supplied by translocation through the mycelium from separate sites and the utilization efficiency is higher when carbohydrate is added to the outer medium. Autoradiography with 14C-glucose, applied at the inner or outer medium, showed the movement of isotope through the mycelium bidirectionarily. Some of the isolates tested formed mycelial strands on the outer surface of inner dish, which morphogenesis was similar to those of Helicobasidium purpureum.
We have compared on the kinds and intensity of symptoms appeared under the different temperatures, i.e., 15°, 23° and 30°C, between the filiform and the enation of mulberry plants, characteristic to mulberry mosaic disease. On the filiform materials, conspicuous filiform symptoms and some ring spots developed, but nothing showed enation symptoms. On the other hand, enations, ring spots and yellowing spots were shown from the enation materials, while filiform symptoms did not developed from them. Effect of temperature on the intensity of symptoms was very different between the enation and filiform materials. On the enation materials collected from Gumma Prefecture, severe symptoms developed when the plants were kept at 23° and 15°C, but no symptom at 30°C, although the enation materials from Shiga Prefecture showed symptoms so slightly that could not discuss the relationships between symptom appearance and temperature. On the filiform materials, symptoms developed severely at 23° and 30°C, and the intensity of symptoms on plants kept at 23°C was higher than those at 30°C, but when plants were grown at 15°C, symptoms were almost masked.
Electrotaxis of zoospores of Phytophthora capsici Leon. was investigated in some organic solutions employing platinum electrodes at a potential gradient of 2V/cm. In deionized water, zoospores oriented and swam to the cathode. The swimming velocity of zoospores decreased as they came up close to the cathode, moved around the electrode with turn and rotation and finally ceased the motion. A repulsion zone was quickly formed at the anode. On the contrary, in 10-2M solutions of sodium maleate, malate, malonate, succinate, glutamate, aspartate and others, zoospores were markedly attracted to and aggregated at the anode. The repulsion zone became larger with the decreased concentration of the solutes. The zone was also formed around the cathode. With some of mono-and disaccharides, zoospores were accumulated around the cathode as in deionized water regardless of the concentrations. These results would imply that all of these phenomena in the zoospore attractions toward the electrodes could not satisfactorily be explained by the theories of concentration gradient or electrostatic forces. Furthermore, no difference in electrotactic responses of zoospores among D- and L-malate and aspartate suggests that there is no direct relationship between the electrotaxis and the metabolism of zoospores.
Vaccination of tomato plants with an attenuated tomato strain of TMV (L11) affords good protection against infection with the virulent parent virus (L). The effects of time from vaccination (L11) to inoculation (L) are reported in this paper. The sap of L11-infected tomato leaves diluted either 10 or 10, 000 times of leaf weight was used as the vaccine. The intervals between vaccination and inoculation were at 0, 1, 2, 4, 8, 24, 48 and 168 hours. The tomato seedlings were 13-18 days old when vaccinated. One of their cotyledons was inoculated with L11 and the other one with L, to test the degree of protection. The symptoms on the tomato seedlings were recorded as regards chlorosis, mosaic on leaves, stunting, and malformation of leaves, at intervals of 3 to 4 days after inoculation of L. The plants inoculated with L alone began to show chlorosis 7 days after inoculation, followed by mosaic, and 5 days later they mostly showed these symptoms together with stunting. Only a few plants inoculated with L11 alone showed chlorosis and stunting. In the plants inoculated with L 1 to 8 hours after vaccination, 40 to 60 per cent showed chlorosis and stunting: even the plants simultaneously inoculated with L11 and L showed protection to a certain extent. The plants inoculated with L 24 hours or more after vaccination showed such a remarkable effect that chlorosis and stunting appeared only in 10 per cent of them. Mosaic symptoms appeared more slowly in the plants vaccinated and inoculated with L after 24 hours or more, than in the plants inoculated with L alone. The mosaic was milder in all the vaccinated plants than in the non-vaccinated plants. With the vaccine diluted 10, 000 times, the preventive effects were incomplete when the plants were inoculated with L 24 or 48 hours after vaccination, but with the interval of 168 hours the vaccination gave good results. From the results of experiment on removal of cotyledon inoculated with the vaccine, it was estimated that the attenuated virus began to move from the inoculated cotyledon to other parts of the plant in 2 or 3 days after inoculation.
The nucleic acids in TMV-infected tobacco leaves were analyzed mainly by MAK column to make clear the mode of virus multiplication in the host. The nucleic acids of tobacco leaf-disks infected for 5 days with TMV contained an unusual RNA that was resistant to RNase of 0.5μg/ml and had TMV-RNA type base ratio. This fraction was eluted near DNA peak on MAK column. The rate of P32 incorporation into 18s ribosomal RNA from infected leaf-disks decreased as compared with that into the same RNA from uninfected leaf-disks. Treatment of uninfected leaf-disks with MC markedly reduced the rate of P32 incorporation into all the RNA fractions, whereas, in infected leaf-disks, the same incorporation into 28s RNA which contains TMV-RNA was not affected by MC treatment. From these results, the mode of TMV multiplication in tobacco leaves at the early infection stage is discussed.
Rhizoctonia solani, Fusarium oxysporum and Pythium aphanidermatum in the saprophytic behaviour usually inhabited on debris in 0-20cm of soil depth, and P. aphanidermatum was in upper layer, R. solani in middle and F. oxysporum in deeper of soil, respectively. But, in overwetting soil, many of them immigrated into upper layer than in moderately moist soil. In each depth of soil phosphate and nitrogen decreased gradually with depth but carbon hydrate decreased suddenly at 30cm of depth. The survival ratio of R. solani inoculated in soil dug up from different depth decreased suddenly downwards of 30cm at 3 weeks after inoculation. It is considered that, carbon sources in soil determine the inhabitation of the fungi. P. aphanidermatum, inoculated in soil with rice straw, decreased in a half for 1 month, R. solani did for about 3.5 monthes and F. oxysporum did for about 5 monthes. Whereas P. aphanidermatum was lost after 3 monthes on straw in summer, a few of R. solani and F. oxysporum were surviving on it for 7 monthes. These 2 pathogens were dead more rapidly in submerged soil than in moderately moistened soil. P. aphanidermatum grew well on fresh straw in soil, but R. solani and F. oxysporum grew well on decomposed one by soil microben. From these results it is suggested that, though these 3 pathogens are alive in soil by utilization of plant debris, one of the factors determinating the colonized and active survival abilities of them are the components of debris on which they arrive and grow.