Aquatic Plant Control Research Program. Biological Control of Hydrilla verticillata (L.f.) Royle with Lytic Enzyme-Producing Microorganisms

摘要

Bacteria and fungi isolated from the microsphere of hydrilla were screened for production of the lytic enzymes cellulase and pectinase. Lytic enzyme-positive isolates were successively subcultured on restrictive media in the laboratory to enhance enzyme production. Twenty-two of the enzyme-enhanced isolates were assayed using hydrilla sprigs in test tubes to determine their ability to infect the plant. Seven cellulase-producing fungi produced significantly greater damage to hydrilla than exhibited by treated or untreated controls. Six of these were assayed using hydrilla plants in 75.7-l aquaria. None of the fungi significantly damaged hydrilla in the aquaria. Inoculum for the aquarium assay consisted of filtered organisms, whereas whole inoculum including nutrient growth medium (PDB) and accumulated exogenous metabolites (e.g. cellulase) was used in the preliminary test tube assay. This difference in inoculum for the two assays and the negative results of the aquarium assay suggested that the isolates required nutrient or metabolite supplements in the inoculum to inflict damage on hydrilla. Results showed that whole inoculum produced significantly greater damage than filtered organisms and that nutrients must be present for the organisms to impact hydrilla. Results of the two assays also showed that greenhouse plants were more resistant to attack than field plants.