Biocontrol Potential of Fungal and Oomycete Phytopathogens by Myxobacterial Strains

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 four different phytopathogenic fungi, as follows: two isolates of Rhizoctonia solani from 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. non-contact and contact inhibition on agar media between phytopathogens and myxobacteria were visually discernible. This distinction potentially reflects the activity of low-molecular-weight metabolites and high-molecular-weight lytic enzymes, respectively. In a pot soil study, the inhibitory effect of a mixture of two strains of myxobacteria against 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 an in vivo inhibitory effect of myxobacteria against Rhizoctonia. The 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.