Abstract
The manner of use of the carbon source during the sclerotium formation of Rhizoctonia solani Kühn AG-1 (IA) was examined. Both the hyphal weight and the number and weight of sclerotia increased with carbon concentration. When the shift of the carbon source during the formation on the check medium (1% glucose) was investigated with 14C-labeled glucose, almost the entire carbon source was consumed in the time interval from the initial to the maturing phases. CO2 evolution also showed a similar tendency. The residual carbon was detected at concentrations of carbon source above 1%, increasing linearly with the concentration. The branching internodes and cell lengths of hyphae were shorter at higher concentrations, meaning that a certain amount of carbon is essential for hyphal branching and septation, the first steps in the sclerotium morphogenesis. The activities of enzymes, malate dehydrogenase and isocitrate dehydrogenase, associated with TCA cycle became more vigorous with the carbon concentration. The energy estimated from the CO2 evolution, required to produce sclerotia, was 4-10kcal/g. These results show that sclerotium morphogenesis requires a large amount of the carbon source because of the substrates and energy needed for enlargement, development and maturation. The hyphae, once developed, were hydrolyzed and reused for the sclerotium formation if the carbon source in the media had become depleted during the hyphal development.
