Biocontrol potential of fungal and oomycete phytopathogens by myxobacterial strains

Authors: Ismaiel, Adnan; Lakshman, Dilip; Millner, Patricia

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Resilient cropping systems require integrated management practices that include biocontrols as well as site appropriate cultivar selection, and soil health/fertility measures to maintain productivity. The aim of this study was to investigate the antagonistic and biocontrol activities of 13 species of predatory, swarming myxobacteria, representing four different genera, against three major soilborne, root disease fungi: Rhizoctonia solani, Sclerotinia sclerotiorum, and Pythium ultimum. Three myxobacteria strains were determined to be highly inhibitory from among the 13 strains tested. A soil challenge study showed that a mixture of two inhibitory Myxobacteria strains suppressed disease development in cucumber seedlings by two fungal root rot (Rhizoctonia) isolates. This is the first report of the in vivo inhibitory effect of myxobacteria against this plant pathogen. Survival of the predatory Myxobacteria xanthus strains in sterile soil amended 1:1 with sterilized rabbit manure, was maintained for up to five weeks compared to only a one-week survival in unamended controls. These results indicate that even sterile organic amendment can contribute to increased suppression of the plant pathogen and enriched concentrations of myxobacteria in soil. This information would be useful to plant pathologists, extension agents, farmers, and the biocontrol industry.

Technical Abstract: Myxobacteria, a group of swarming, predatory soil bacteria, are of interest because of their biocontrol potential. In this study, the inhibitory effects of 13 strains of myxobacteria were examined against three different phytopathogenic fungi, Rhizoctonia solani two isolates of different AG groups, and one isolate each from Sclerotinia sclerotiorum and the oomycete, Pythium ultimum. Inhibition levels varied among phytopathogens, with slow-growers being more susceptible than fast-growers. Myxococcus xanthus BS 248, M. flavus ATCC 29617, and M. coralloides BS249 were the most inhibitory strains tested. Contact and non-contact inhibitions on agar media between phytopathogens and myxobacteria were visually discernible. This distinction potentially reflects activity from low molecular weight metabolites compared to high-molecular-weight lytic enzymes. In a pot soil study, the inhibitory effect of a mixture of two strains of Myxobacteria on two strains of R. solani was apparent from the reduced disease in cucumber seedlings compared to controls without myxobacteria. This is the first report of the in vivo inhibitory effect of myxobacteria against Rhizoctonia. Survival of M. xanthus BS248 in sterile soil amended with rabbit manure (1:1) increased up to five weeks compared to one week in soil without the manure, suggesting that organic amendment could enrich Myxobacteria in soil.