Macerating Enzymes Produced by Rhizopus oryzae in Infected Mulberry Roots

Rhizopus oryzae, the causal agent of Rhizopus rot of mulberry, was examined for its ability to produce macerating enzymes in planta and in vitro. When segments of healthy mulberry roots were immersed for 24 h at 30 C in pH-adjusted crude extracts from roots of mulberry infected naturally or inoculated with R. oryzae, or in the culture filtrate of the fungus in liquid medium containing mulberry roots or pectin, maceration measured by the weight decrease of the immersed segment was detected in all of these crude extracts, and the highest activity was observed under acidified conditions. Activities of cellulase, polygalacturonase, pectate lyase, and pectin lyase, but not protease were detected in crude extracts of the fungusinoculated roots and in culture supernatant in liquid medium containing the roots. These results suggest that these macerating enzymes are produced in the infected roots. The crude extract of the fungal culture grown in pectin liquid medium, which also macerated the roots, showed only the activity of three pectic enzymes (polygalacturonase, pectate lyase and pectin lyase). Polygalacturonase may play an essential role in the maceration of mulberry roots by R. oryzae