Beauveria bassiana, a dual purpose biocontrol organism, with activity against insect pests and plant pathogens.

Microbial control of plant pathogens and insect pests is an important component of efforts to reduce reliance on chemical pesticides and increase sustainability of agriculture. Although the number of registered microbial products has increased in recent years, many potential biopesticides have either not been developed for commercial use, or have had limited success, due to their pathogen or pest specificity, inconsistent performance across environments, or a lack of understanding of the mechanism(s) of biocontrol, resulting in ineffective use. Beauveria bassiana is a commercially available entomopathogenic fungus with an extensive host range of insect pests. Isolates of this fungus have been shown to be endophytic in specific crop plants, and in some cases, endophytic colonization has been linked to the ability ofthe fungus to control insect pests. With few exceptions, research on B. bassiana as a potential biological control for plant pathogens has been limited to in vitro studies on growth inhibition and cell lysis of plant pathogens. The potential of B. bassiana to control important plant pathogens in situ remains largely unknown. We have evidence that B. bassiana 11-98, originally isolated from an infected click beetle in Scott County, Tennessee, U.S.A., can control damping-off of tomato, caused by the soilborne fungal pathogen, Rhizoctonia solani, and can provide protection to cotton against a seedling disease complex in field soils. Furthermore, seed treatment with B. bassiana isolate 11-98 has resulted in endophytic colonization of tomato seedlings in a gnotobiotic system. The mechanism(s) of biocontrol by B. bassiana against plant pathogens, and whether or not endophytic colonization is a critical component of biocontrol are currently being investigated. Development of biopesticides that can control both plant pathogens and insect pests will have enormous value for plant protection in U.S. agriculture. Such biopesticidal organisms would be similar to wide spectrum pesticides with their potential for a significant reduction in pest management costs. However, unlike most chemical products, which have activity only against insects or plant pathogens, these biocontrol agents would have activity against both. Furthermore, disease and pest control with microbial agents offer the environmental advantages associated with biological control.