Studies in the Physiology of Parasitism

Fusarium moniliforme secreted macerating enzymes in liquid media only when these contained certain natural extracts, pectic substances, or galacturonic acid. Apple extract was unsuitable for enzyme secretion and also inhibited enzyme secretion in synthetic media otherwise suitable. Protopectinase activity of solutions was highest in the pH range 8·0–9·0, was rapidly lost at temperatures above 50–60° C., and was reduced by concentrations of phosphate higher than 0·02 M. The enzyme was partially purified by precipitation in 60 per cent. acetone at pH 6·0. Protopectinase solutions also contained an enzyme which reduced the viscosity of solutions of various pectic substances. The properties of this enzyme were, in general, similar to those of protopectinase. When activity of enzyme solutions was measured by the liberation of reducing groups, pectate solutions were more rapidly degraded than were solutions of a high methoxyl pectin, particularly in the early stages of the reaction. Paper chromatography of the products formed showed that pectate and pectin were degraded in different ways. Although the pathogen readily secreted protopectinase in potato extract, potato tubers were not readily parasitized. In contrast, Fusarium avenaceum which readily attacked tubers, secreted little protopectinase in potato extract.