Rhizoctonia solani Kuhn の菌学的および病理学的研究
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This thesis deals with some subjects for the causal agent of soil borne disease, Rhizoctonia solani Kuhn. The conclusions are summarized below. 1) Grouping with the zymogram A collection of 48 isolates selected from various anastomosis groups of R. solani showed at least 9 distinct zymograms. Isolates from the rice (the sasaki type), or its relatives showed the zymogram pattern named Zym-1. However, isolates in the same anastomosis group (AG-1) from other host plants (the web-light type) exhibited several other different zymograms. Isolates of AG-2-2 from the mat rush (Igusa), rice (quasi-sheath blight) and sugar beet gave Zym-2-2A which resembled Zym-1. Other members of AG-2-2 from the sugar beet exhibited a different zymogram, Zym-2-2B. An isolate of AG-2-1 gave the pattern Zym-2-1 which was quite different from all the other zymogram patterns. Isolates from potato (AG-3) showed a characteristic zymogram designated Zym-3. Similar zymograms were given by some isolates of anastomosis group AG-5 which also came from potato. The zymogram groups roughly agreed with the anastomosis groups, and sometimes correlated more closely with the ecological types. These results will serve as a clue to the revision of taxonomy of R. solani. 2) Morphological study on sclerotium The process of the sclerotial development of R. solani was compared with that of Sclerotinia sclerotiorum by a scanning electron microscope. The mature sclerotia of R. solani were 2∿3mm in diameter, and their outer and inner layers were dark brown in color, whereas those of S. sclerotiorum were 4∿6mm, their outer layer (rind) consisted of vacuous cells, and their inner layer (medulla) was composed of white watery cells. In the case of R. solani, the initials were formed by intertwining of several hyphae followed by branching of normal hyphae. The sclerotial surfaces from the white to mature sclerotial stages were covered with dense hyphae. Inner and outer parts of the sclerotia showed a honey-comb structure as observed by sectioning. On the other hand, initials of S. sclerotiorum were developed by intertwining of elongated, curved hyphae. No differentiation of inner and outer layers were observed at the white sclerotial stage. However, as the pigmentation proceeds, two or several layers vacuoled as rind and the inner parts consisted of hyphal fusion and anastomosis, which have few intercellular spaces, as medulla. The change of hyphae covering sclerotial surface was recognized during the maturation. 3) Effects of physical factors on sclerotial longevity The order of high-temperature tolerance at the different morphological stages was hyphae < initials < white sclerotia < immature sclerotia < mature sclerotia. The mature sclerotia, in particular, resisted 3∿7℃ higher temperatures than the other stages. R. solani was more tolerant to high temperatures than S. sclerotiorum. On the other hand, R. solani at all the stages starting from the white sclerotia survived even under the UV irradiation applied for 10 days. The initials which are formed by hyphal branching followed by aggregation and interweaving became to be more tolerant to UV, suggesting that striking physiological changes took place at the initial stage. The mature sclerotia of the 2 fungi died at pH4∿5,but survived pH's above 6. The sclerotia immersed in pure water at 25℃ survived at a high ratio but died rapidly at 35℃; especially the sclerotia of S. sclerotiorum died within 7 days. 4) Changes in enzymatic activity during the sclerotium formation The activity of malate dehydrogenase was higher in sclerotia than in hyphae. On the other hand, glucose-6-phosphate dehydrogenase and phosphogluconate dehydrogenase showed higher activity in young hyphae in which sclerotia were not formed. The activity of alkaline phosphatase was higher in younger hyphae, decreasing with hyphal aging, whereas that of acid phosphatase increased with the aging of hyphae. These results may indicate that the s
- 琉球大学の論文
- 1997-12-01