Interaction between the plant growth-promoting fungus Phoma sp GS8-2 and the arbuscular mycorrhizal fungus Glomus mosseae: impact on biocontrol of soil-borne diseases, microbial population, and plant growth

The influence of the interaction between Phoma sp. GS8-2 (GS8-2) and the arbuscular mycorrhizal fungus Glomus mosseae (Gm) on the development of soil-borne diseases, microbial population, and plant growth in cucumber, bentgrass and tomato plants was investigated under controlled conditions. The composite inoculation of GS8-2 and Gm yielded varied effects on suppression of symptoms of soil-borne pathogens depending on the host-pathogen combination involved. The GS8-2+Gm had neutral effect in reducing damping-off disease of cucumber caused by Rhizoctonia solani AG-4 and the crown and root rot disease of tomato caused by Fusarium oxysporum f. sp. radicis-lycopersici (Forl), but exacerbated the brown patch disease caused by R. solani AG2-2 in bentgrass. In tomato plants, Forl populations in the roots and rhizosphere were significantly reduced by GS8-2+Gm. Results also show that the composite inoculation of GS8-2 and Gm resulted to a synergistic effect on the reduction of fungal and bacterial populations in roots and rhizosphere of the plants. Plant growth enhancement was due to the individual effect of GS8-2 or Gm but not their interaction. GS8-2 root colonization of cucumber and tomato plants decreased significantly in dual inoculated plants compared to plants inoculated with GS8-2 alone; while no significant differences were found in the Gm root colonization of the three plant species indicating that GS8-2 had no effect on Gm.