Biocontrol agents applied individually and in combination for suppression of soilborne diseases of cucumber

The soilborne pathogens Rhizoctonia solani, Pythium ultimum, and Meloidogyne incognita can cause severe economic losses to fieldand greenhouse-grown cucumber. A collection of bacterial isolates and isolates GL3 and GL21 of Trichoderma virens were screened for suppression of diseases caused by these pathogens. T. virens isolates GL3 and GL21 provided the most effective suppression of damping-off caused by R. solani in greenhouse bioassays. Burkholderia ambifaria BC-F, B. cepacia BC-1, and Serratia marcescens N1-14 also provided significant suppression of R. solani relative to the pathogen check in some experiments. T. virens isolates GL3 and GL21 and S. marcescens isolates N1-6, N1-14, and N2-4 provided the most consistent and effective suppression of damping-off of cucumber caused by P. ultimum in growth chamber experiments. No microbial treatment containing individual or combined microbes significantly suppressed populations of M. incognita on cucumber or improved plant vigor in greenhouse bioassays. T. virens GL21 applied as a granular formulation, in combination with B. cepacia BC-1 or B. ambifaria BC-F applied as a seed treatment, significantly improved suppression of damping-off caused by R. solani over individual applications of these microbes in at least one experiment. Treatments combining B. cepacia BC-1, B. ambifaria BC-F, or S. marcescens isolates N114 or N2-4 with T. virens GL21 in R. solani biocontrol assays always resulted in plant stands that were similar or greater than treatments containing individual applications of these microbes. B. ambifaria BC-F combined with T. virens GL21 in seed treatments resulted in significantly improved suppression of damping-off caused by P. ultimum in two of three experiments. Populations of T. virens GL3 and GL21 were both substantially reduced after coincubation with B. cepacia BC-1, or S. marcescens isolates N1-14 or N2-4 for 10 to 12 d in cucumber rhizospheres. Populations of T. virens GL21 were slightly reduced after coincubation with B. ambifaria BC-F. Results presented here substantiate other studies reporting enhanced biocontrol performance e front matter r 2004 Elsevier Ltd. All rights reserved. opro.2004.07.004 ing author. Sustainable Agricultural Systems Laboratory, USDA-ARS, Room 140, Building 001, 10300 Baltimore Avenue, Beltsville, , USA. Tel.:+1-301-504-5680; fax:+1-301-504-8370. ess: [email protected] (D.P. Roberts). ress: Geo-Centers, Inc., Naval Health Research Center, Environmental Health Effects Laboratory, Wright-Patterson Air Force Base, . ress: Bowers Consulting Services, Laurel, MD 20707, USA. ress: Indiana University School of Dentistry, 1121 West Michigan St., Room 270, Indianapolis, IN 46202, USA. merly of the Biocontrol of Plant Diseases Laboratory, Henry A. Wallace Agricultural Research Center, USDA-ARS, Beltsville, A.