ARS | Publication request: Inhibition of Aspergillus flavus in soil by antagonistic Pseudomonas strains reduces the potential for airborne spore dispersal

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 26, 2010
Publication Date: June 1, 2010
Citation: Palumbo, J.D., O Keeffe, T.L., Kattan, A., Abbas, H.K., Johnson, B.J. 2010. Inhibition of Aspergillus flavus in soil by antagonistic Pseudomonas strains reduces the potential for airborne spore dispersal. Phytopathology. 100:532-538.

Interpretive Summary: Two bacterial strains were previously isolated from corn soil and corn roots and identified as Pseudomonas chlororaphis and Pseudomonas fluorescens. These strains showed inhibition of the aflatoxin-producing corn pathogenic fungus, Aspergillus flavus, in laboratory media. Tests to measure inhibition of this fungus in soil showed that both bacteria were effective at inhibiting A. flavus in soil, and that the P. chlororaphis strain was more effective than the P. fluorescens strain. To show whether using bacteria to reduce fungal growth in soil had any further effects, we designed a small wind tunnel and used it to measure how many A. flavus fungal spores could be blown in wind across a one meter distance. These experiments showed that the bacteria were effective in reducing the number of spores carried by wind. This study suggests that soil application of these bacteria may be useful in reducing populations of toxin-producing fungi under agricultural conditions.

Technical Abstract: Pseudomonas chlororaphis strain JP1015 and Pseudomonas fluorescens strain JP2175 were previously isolated from Mississippi cornfield soil samples and selected for their growth inhibition of Aspergillus flavus in laboratory culture. In this study, the antifungal activity of these bacterial strains against A. flavus in soil coculture was determined. Growth of A. flavus was inhibited up to 100-fold by P. chlororaphis strain JP1015 and up to 58-fold by P. fluorescens strain JP2175 within 3 days following soil coinoculation. A. flavus propagule densities after 16 days remained 7-fold to 20-fold lower in soil treated with either bacterial strain. Using a bench-scale wind chamber, we demonstrated that treatments of soil with P. chlororaphis strain JP1015 and P. fluorescens strain JP2175 reduced airborne spores dispersed across a 1 meter distance by 75-fold to 1000-fold, and 10-fold to 50-fold, respectively, depending on soil type and inoculum level. These results suggest that application of these bacterial strains may be effective in reducing soil populations of mycotoxigenic fungi, thereby reducing fungal spore formation, and ultimately reducing the potential for corn infection via airborne transmission.