Towards biocontrol of ophiostomatoid fungi by plant growth-promoting rhizobacteria

Ophiostomatoid fungi, Leptographium terebrantis and Grosmannia huntii, are among the most important agents of wood blue stain and root disease of Pinus species. A number of physical, chemical, and cultural strategies adopted to minimise the impact of these fungi are of limited success. Biological control of tree diseases with plant growth-promoting rhizobacteria (PGPR) is attractive given that they provide an alternative and supplement to synthetic chemicals without negative impact on the environment. While a significant number of studies have shown the ability of PGPR to control pathogens of agricultural plants, studies to understand the activity of PGPR against ophiostomatoid fungal pathogens of conifers is still lacking. To understand the utility of PGPR in treating blue stain in woods, twenty-seven Bacillus velezensis strains and single strains of Paenibacillus peoriae and B. altitudinis that had previously shown antibiosis against plant pathogens from six different genera were tested for in vitro antibiosis against L. terebrantis and G. huntii. To understand the efficacy of PGPR in controlling root-disease, Bacillus pumilus SE-34 and INR7, and Serratia marcescens (90-166), previously reported to have efficacy against a root pathogen in conifer, were tested for their capacity to induce resistance of P. taeda to these fungi. All PGPR strains inhibited the growth of L. terebrantis and G. huntii in vitro. In a second experiment, specific PGPR treatment resulted in increased seedling dry matter biomass and reduction of diseased tissue. The results demonstrate tested PGPR strains may have potential as biocontrol agents to the tested ophiostomatoid fungi.