In vitro assessment of antifungal activities of antagonistic fungi towards pathogenic Ganoderma boninense under metal stress

Three antagonistic fungi (Trichoderma asperellum isolate T2, Diaporthe sp. isolate WAA02, Penicillium citrinum isolate BTF08) were evaluated for their tolerance to metals and the impact of the metals on their antifungal expression against a model pathogen (Ganoderma boninense). Experiments performed include metal tolerance and dual culture assays, viability test, SEM and Pearson Correlation test. In the presence of metals, growth and antifungal expression of the endophytes were inhibited, particularly by Cd²⁺ (50 ppm), Zn²⁺ (100 ppm), and Cu²⁺ (100 ppm). The antifungal expression was least affected by the presence of Pb²⁺ (60-100% inhibition) but was 0% in Al³⁺, Cd²⁺, Cu²⁺ and Zn²⁺ (200 ppm onwards). The absence of antifungal expression was associated with their poor growth in these metals (r = 0.6080-0.8911). Clearly, the growth and antifungal activity of these isolates are influenced by the metal species and concentrations, and is an important factor for future development of antagonistic fungi as biopesticides.