One side of potato tuber slices having different thickness was inoculated with such dense zoospore suspensions of an incompatible race of Phytophthora infestans as to infect almost all of the surface cells. The less the number of layers of underlying healthy cells, the more prolonged the time taken for the infected cells to die hypersensitively. Browning of the infected cells occurred more rapidly in thick slices than in thin slices. These results suggested that healthy cells underlying the infected cells play an important role in the hypersensitive death of the infected cells and also supply substances necessary to localize the infection.
Rice blast disease preventive activities of seven amino acid derivatives were examined by using rice seedlings of the 4- or 5- leaf stage. Because N-lauroyl-L-valine (No.5) showed the most constant activity among them, it was used as the test compound in further experiments, and the following experimental results were obtained. Lauric acid, L-valine and their mixture showed lower activities than that of No.5. In comparison with activities of optical isomers of valine, no significant difference was found among them. Among various salts and esters of N-lauroyl-L-valine tested, only sodium and potassium salts were as effective as the free compound, whereas calcium salt, and methyl and ethyl esters had low preventive activity. In case of substituting other amino acids for valine residue in N-lauroyl-L-valine, L-proline, L-methionine, L-leucine and DL-alanine derivatives were as effective as No.5, whereas in case of replacing lauric acid (C12) with other fatty acids, the protective effects reduced as increasing or decreasing the number of carbon atoms of substituted fatty acids.
Studies on the influence of TMV in tobocco having M. javanica infection revealed that TMV influences the host-parasite relationship of M. javanica. The virus-nematode infection complex had marked effect on the host. Higher nematode population was observed in roots and soils of TMV infected tobacco plants. The maximum synergistic interaction between TMV and M. javanica to the tabacco plants occured when both pathogens infect the host simultaneously.
Mode of perpetuation of 4 pathogens viz. Cercospora carthami Sundararaman and Ramakrishnan, Ramularia carthami Zaprometov, Cercospora linicola Pavgi and Rathaiah and Cercospora sesamicola Mohanty inciting leaf spot diseases of safflower, flax and sesame has been investigated. C. carthami and C. linicola perpetuate through a) the vegetative saprobic mycelium and b) viable stromata embedded in the crop debris. R. carthami and C. sesamicola perpetuate only through the viable sclerotia in the crop debris.
Movement of the stripe virus in rice leaf was intercepted or delayed by pre-treatments known to affect the function of phloem, viz., with chemicals such as sodium azide, monoiodoacetic acid, dinitrophenol, chloroform and alcohol, cooling or steam-heating at the portion about 2cm below the area to be fed by viruliferous smaller brown planthoppers. Results of severing tests showed that the virus moved downward in the inoculated leaf at a rate of 25 to 30cm per hour. The virus given off by brown planthopper was recovered at a distance of 5 to 7cm from the site of feeding, by using Unkanodes albifascia, hopper of outstanding compatibility with stripe virus. Rate of virus movement was enhanced by increase in number of hoppers for inoculation and by time for feeding longer than 1 hour. Treatments such as cutting off roots, folding leaf blades or exposing to low temperature (15C), effected adversely. Movement in highly resistant varieties was remarkably hindered as compared with susceptible varieties. Initial symptoms usually appeared on the upper leaf next but one from the inoculated leaf. The portions where disease symptoms developed coincided with the tissue in which cell division was taking place at the time of inoculation. The presence of virus was verified by hemagglutination test in the tissues of top extending from the leaf sheath of next upper leaf and leaf blade next but one from the inoculated leaf to the uppermost leaf primordium, and in root. In the leaves which had been expanded at the time of inoculation there was no evidence of virus multiplication. These results suggest that the stripe virus injected by the hopper passes through phloem, without multiplying at the feeding site, and reach younger tissues feasible for multiplication.
In October 1969, the perithecia of citrus melanose fungus, Diaporthe citri (Fawc.) Wolf, were found in the orchard of Satsuma orange in Kanagawa Prefecture. The author conducted experiments to know the time and environmental conditions on perithecia formation, and also to ascertain the virulence of ascospores against citrus fruits comparing with that of pycnospores. Results obtained are summarized as follows: Perithecia of the fungus were found mainly on dead twigs left on the ground and also in some cases on the dead branches or twigs remained on trees. Its morphological characters were accordant with those of Diaporthe citri (Fawc.) Wolf and other workers. The fungus isolated from ascospores produced Phomopsis-type pycnospores on potato dextrose agar and citrus twigs. The perithecia were formed on the twigs of Satsuma orange inoculated with pycnospores. The melanose symptoms of the fruits were induced by the inoculation with ascospores of the fungus. On dead and pruned branches which had been left on the ground of citrus orchard in February to March, immature perithecia were formed in August and September. They became matured in September and October of the same year. In laboratory tests, perithecia of the fungus were formed on the inoculated dead twigs only under high relative humidity over 95%. Symptoms on fruits appeared 6∼11 days after the inoculation with ascospores. In the early stage of fruit development, they were quite similar to those caused by pycnospores, however in September to October, some differences were recognized: that is melanose spots caused by the former were more circular and slightly larger. When the similar amount of ascospores and pycnospores were inoculated on citrus fruits, the symptoms were severe in the former. From these results, it may be concluded that the virulence of ascospores on citrus fruits is higher than that of pycnospores.
The pycnospore formation of Diaporthe citri was markedly increased when the fungus was cultured under the continuous illumination of “black-light blue” (BLB) fluorescent lamp. The effective wave length was 324 or 355nm, obtained through interference filters. When the young colonies grown under the continuous darkness were exposed to BLB, α-spores were formed at relatively low temperatures and β-spores at high temperatures.