Inhibitory Interactions Between Ceratocystis Ulmi and Several Species of Entomogenous Fungi

Abstract

Inhibition by 14 isolates of nine species of entomogenous fungi against two strains of the Dutch elm fungus, Ceratocystis ulmi (aggressive and non-aggressive), was evaluated under laboratory conditions. Eleven of the 14 inhibited one or both strains of C. ulmi. Different levels of antagonism were observed at different light levels and temperatures. Beauveria bassiana, Metarhizium anisopliae, and Nomuraea rileyi were antagonistic to both strains of C. ulmi under the four tested combinations of light and temperature. Metarhizium anisopliae produced the highest qualitative level of inhibition. The growth rate of the cultures differed Conventional control measures for the Dutch elm disease (DED) have em- phasized control of the insect vectors, Scolytus scolytus Fabr. and Scolytus mul- tistriatus Marsham, mainly due to the inaccessibility of the pathogen, Ceratocystis ulmi (Buis.) Moreau in the xylem vessels of the elm (Holmes, 1980). Several workers (Doane, 1959; Barson, 1976,1977; Doberski, 1981) have reported patho- genicity in tests for control of the DED insect vectors by the entomogenous fungi, Beauveria bassiana (Bals.) Vuill., Metarhizium anisopliae (Metsch.) Sorokin, Pae- cilomyces farinosus (Dicks ex Fr.) Vuill., and Verticillium lecanii (Zimm.) Viegas. The possible use of these entomogenous fungi in biological control of DED requires investigation of antagonistic interactions between vector and control agent, and also between C. ulmi and each entomogenous fungus. Gibbs and Smith (1978) and Webber (1981) identified several fungal antagonists of C. ulmi. The bacterium, Pseudomonas syringae van Hall, has also demonstrated in vivo an? tagonism in studies by Myers and Strobel (1983), and earlier Holmes (1954) showed Bacillus polymyxa to be an effective inhibitor. The objectives of the present study were to assess the interactions between potential vector control agents (such as entomogenous fungi), and two strains of C. ulmi. Fungal antag? onists of C. ulmi would be efficiently brought into action if they were transported