Pathochemical studies on watermelon wilt. (Part 10).

Abstract

(1) Polysaccharide, nitrite, and ethanol, those are responsible for a toxicity to host plants, were detected in the cultural filtrate of Fusarium oxysporum f. niveum, the causal fungus of watermelon wilt disease, in addition to the previously reported metabolic products; phytonivein, fusaric acid, and depolymerase. Polysacchaide was identified as heteropolysaccharide having no glucose and caused wilting of host plants, whereas nitrite and ethanol induced leaf necrosis and epinasty, respectively. However, the fungus did not produce these three substances in the cultural solution so sufficient amount as to explain the importance of the substances for disease development.(2) The continuous production of the toxins during the germination of conidia were determined and were presented in Figure 4. Depolymerase and cellulase activities were recognized as soon as the conidial germination. Ethanol was produced after the slight elongation of germ-tube, thereafter fusaric acid and phytonivein were quantitatively detected. The amount of the toxins produced in vitro per one spore was also estimated.The above in vitro experimental results may give a convenient datum to understand the biochemical mechanism of fungal invasion into host cells. Because, the secretions of depolymerase and cellulase, causing break down of host cell walls, happen at the same time with the spore germination, and nextly secretions of toxins, toxic to living cell, begin. But present thinking suggests that the pathogenesis in generally may be responsible for establishing the hyphal invasion into host cell rather than for the strength of the toxin production, and the actions of the toxins are to be looked for the situation on promoting the disease development, the systemic wilting symptoms.