BIOCONTROL AGENTS APPLIED INDIVIDUALLY AND IN COMBINATION FOR SUPPRESSION OF SOILBORNE DISEASES OF CUCUMBER

Authors: Roberts, Daniel; LOHRKE, SCOTT - FORMER ARS; Meyer, Susan; Buyer, Jeffrey; Bowers, John; Baker, Con; LI, W - HUBEI UNIV, PRC; DESOUZA, J - UNIV MARYLAND; LEWIS, J - FORMER ARS; CHUNG, S - MEGA BIOTECH,S KOREA

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2004
Publication Date: 1/15/2005
Citation: Roberts, D.P., Lohrke, S.M., Meyer, S.L., Buyer, J.S., Bowers, J.H., Baker, C.J., Li, W., Desouza, J., Lewis, J.A., Chung, S. 2005. Biocontrol agents applied individually and in combination for suppression of soilborne diseases of cucumber. Crop Protection. 24:135-141.

Interpretive Summary: Soilborne plant pathogenic fungi and nematodes cause diseases that result in major economic losses to farmers in the United States. Biological control measures for these diseases need to be developed due to environmental problems associated with existing chemical controls. However, biological control has been incorporated into commercial agriculture only on a limited basis. This is due, in part, to inconsistent performance of biological control agents under commercial conditions. We identified a number of bacterial and fungal biological control agents that are effective in suppressing damping-off of cucumber caused by the important soilborne fungal pathogens Pythium ultimum and Rhizoctonia solani. Certain of these biological control agents were compatible in treatments containing combinations of these microorganisms or in cucumber rhizosphere. One particular combination, containing Trichoderma virens GL21 and Burkholderia cepacia BC-1 was more effective than individual applications of these microorganisms in two of three experiments. Combinations of these biological control agents will be tested in future studies to determine if treatments containing these combinations provide more consistent disease suppression under commercial conditions. This information will be useful to scientists devising strategies to improve biological control consistency.

Technical Abstract: The soilborne pathogens Rhizoctonia solani, Pythium ultimum, and Meloidogyne incognita can cause severe economic losses to field-grown and greenhouse-grown cucumber. A large collection of bacterial isolates and isolates GL3 and GL21 of Trichoderma virens were screened for suppression of diseases caused by these pathogens. Isolates GL3 and GL21 provided the most effective suppression of damping-off caused by R. solani in greenhouse bioassays performed in Redi-Earth. Burkholderia ambifaria BC-F and B. cepacia BC-1 both provided significant suppression relative to the pathogen check. T. virens isolates GL3 and GL21 and Serratia marcescens isolates N1-6, N1-14, N2-4, and N4-1 provided the most consistent and effective disease suppression when this collection of microbes was screened for suppression of damping-off of cucumber caused by P. ultimum in growth chamber experiments conducted in Redi-Earth. Culture filtrates from T . virens GL3 and GL21, B. ambifaria BC-F, B. cepacia BC-1 and S. marcescens N1-6, N1-14, and N2-4 suppressed reproduction of the nematode M. incognita in in vitro studies presented here or published elsewhere, suggesting that these microbes have broad-spectrum activity. However, 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 BC-1, applied as a seed treatment, significantly improved suppression of damping-off caused by R. solani over individual applications of these microbes in two of three experiments. Combining BC-1, BC-F, N1-14, and N2-4 with GL21 had no negative effect on suppression of R. solani in any experiment. Combinations of bacteria with other bacteria or T. virens in seed treatments did not significantly alter suppression of damping-off caused by P. ultimum relative to individual application of these microbes. Interestingly, populations of GL3 and GL21 were both substantially reduced after coincubation with BC-1, N1-14, or N2-4 for 10 to 12 d in cucumber rhizosphere but were unaffected or were only slightly reduced in population after coincubation with BC-2 or BC-F. Populations of rifampicin-resistant derivatives of strains BC-1, BC-2, BC-F, N1-14, or N2-4 were unaffected or only slightly reduced in population after coincubation in cucumber rhizosphere with these isolates or GL3 or GL21. We have identified a collection of microbes to be tested alone and in combination in future disease suppression assays conducted under varied environmental conditions with genetically diverse P. ultimum and R. solani isolates.