Introduction

The fungus Gliocladium virens Miller, Giddens and Foster is an important biological control agent (Papavizas, 1985). A formulation of this fungus (strain Gl-21) was recently registered with the US Environmental Protection Agency (EPA) by W. R. Grace & Co. Conn. The formulation was developed in cooperation with the Biocontrol of Plant Diseases Laboratory (BPDL), US Department of Agriculture (USDA) (Lumsden et al, 1991). It is intended for use against dampingoff diseases of vegetable and ornamental seedlings caused by the soil-borne plant pathogens, Pythium ultimum and Rhizoctonia solani in glasshouse operations (Lumsden and Locke, 1989). This fungus is one of the first to be registered for biocontrol of plant diseases and will soon be available in the US for commercial use in glasshouse applications under the trade name, GliogardTM

Certain criteria were considered important in the early stages of development of biocontrol agents (Lumsden and Lewis, 1989). In the development of a screening method for the selection of an appropriate micro-organism, the following points were considered. The screening would involve: (1) the use of a relatively uniform, commercially available soil-less medium that is used extensively in commercial glasshouses where the disease problem occurs; (2) targeted pathogens were selected that are important in the confines of a glasshouse where use of a biological control agent would probably be most successful because of a relatively uniform environment; (3) microorganisms indigenous to the US were selected because non-indigenous micro-organisms might be conceived as more likely problems for the US environment; (4) a single isolate of a biocontrol agent for control of both pathogens was preferred over a mixture of isolates; and (5) a high value crop, important in the ornamental production industry, was selected to defray the cost of development and registration.