Effect of propagule size on the in vitro production of polygalacturonase and cellulase by Rhizoctonia solani

Abstract

The physiological behavior of large (250–500 microns (μ)) infective and small (50–150 μ) non-infective mycelial fragments (propagules) of Rhizoctonia solani was compared. Liquid Czapek's medium containing sodium polypectate (NaPP) as the sole carbon source was inoculated with equal amounts (on a dry weight basis) of each kind of propagule. At NaPP concentrations of 0.005%–0.25% large propagules produced more polygalacturonase (PG) after a shorter period of incubation than small ones, whereas no differences in PG activity were observed at 1% NaPP. Differences in PG activity between large and small propagules were also observed in a medium consisting of 1:50 dilution of potato extract, but not in richer media such as potato dextrose broth and bean hypocotyl medium. These differences did not depend on pH of the medium or dry weight of the mycelium. Germination percentage of the large propagules and length of their emerging hyphae were greater than those of the small ones in media containing 0.005%–0.25% NaPP. Extracellular cellulase activity in Czapek's medium containing 0.25% carboxymethyl cellulose was also higher and appeared earlier in large propagules as compared with small ones. Viscometric and colorimetric methods for detecting PG and cellulase activities produced similar results. It is suggested that the capacity of the large propagules to produce hydrolytic enzymes at low nutrient levels may be important for their parasitic activity.