Production of Conidial Biomass of Trichoderma harzianum for Biological Control

Fungi in the genus Trichoderma are promising biological control agents (bioprotectants) against plant diseases. Biomass used for biological control must be inexpensive to produce. It should be capable of being dried with retention of a high level of germinable propagules, be insensitive to environmental fluctuations (e.g., temperature and humidity), and possess a long shelf life. In this work, we show that the minimal media Czapek Dox and Richard's medium supported a high level of conidial production of T. harzianum, but that overall yields were low. The addition of V8 juice to these media increased yields by 8- to 16-fold, but only 1 to 10% of the conidia produced were viable after vacuum drying. The addition of an osmoticum, i.e., polyethylene glycol (PEG), MgCl(2)center dot 6H(2)O, or mannitol, to Richard's medium with VS juice (RMS) provided a high level of conidial production, and the conidia were resistant to drying in vacuum. Conidial preparations from RMS + PEG were less variable in numbers of colony-forming units per gram than those from RMS. Further, spores produced in RMS + PEG in the laboratory were more effective than spores produced in a commercial fermenter in a medium without added osmoticums in protecting cucumber seeds and seedlings against attack by Pythium ultimum. Spores produced in RMS + PEG had higher levels of trehalose than those produced in RM8; the higher trehalose levels may be associated with the superior level of performance and the desiccation tolerance of spores produced in RM8 + PEG. (C) 1991 Academic press, Inc.