A novel role for Trichoderma secondary metabolites in the interactions with plants

Secondary metabolites play a pivotal role in the antagonistic activities of some biocontrol species of Trichoderma resulting in the suppression of plant pathogens, but their involvement in complex interactions with plants has not been specifically studied. In this work the major secondary metabolites produced by biocontrol strains of Trichoderma (T. harzianum strains T22, T39 and A6, and T. atroviride strain P1) have been investigated for their effect on plant growth promotion. An auxin-like activity was observed on etiolated pea (Pisum sativum) stems treated with harzianolide and 6-n-pentyl-6H-pyran-2-one (6PP), which also affected the growth of tomato (Lycopersicum esculentum) and canola (Brassica napus) seedlings. The ability of these molecules to induce systemic defence responses in planta was also investigated. Tomato and oil-seed rape seedlings were treated with the metabolites and then inoculated with a spore suspension of Botrytis cinerea or Leptosphaeria maculans, respectively. In both cases, a reduction of disease symptoms was observed, particularly on 6PP-treated plants. Moreover an over-expression of pathogenesis-related (PR) proteins was also detected in treated plants. These results clearly indicate that secondary metabolites of Trichoderma spp. may have a role in both plant growth regulation and activation of plant defence responses.