In vitro and in vivo biocontrol studies against Botrytis cinerea, the causal agent of grey mould in Hydrangea macrophylla

Necroses on aerial parts of Hydrangea macrophylla were regularly observed in plant storage chamber at 2°C in Hortensia France company. A total of 34 Botrytis isolates were collected from Hydrangea plants and their environment. To develop biocontrol methods against Botrytis, eight Trichoderma isolates were collected from Hydrangea or the plant soil substrate in the same cold room. Two Trichoderma isolates (E10SM, E014) from this study and one reference isolate (M03) exhibited a high degree of in vitro parasitism against B. cinerea, by comparison with Trichoderma C04 reference isolate (no parasitism). Culture filtrates of isolates E014 and M03 also showed significant in vitro antibiotic properties against B. cinerea growth. A pathosystem H. macrophylla – B. cinerea was set up in the greenhouse, with the inoculation of leaves using mycelial explants selected as the best infection mode. Using this pathosystem, a biocontrol assay showed a significant effect of M03 isolate towards B. cinerea, using Trichoderma conidia applied to leaves 5 h prior pathogen inoculation. After elicitor addition (B. cinerea grinded mycelia) in Trichoderma cultures, antagonistic potentialities of isolate C04 towards the pathogen was highly enhanced, reaching the inhibition level assessed with isolate M03 grown without elicitor. Optimisation of Trichoderma culture filtrates for antagonistic abilities was investigated, and specific cultural conditions were selected for M03 (12 g L⁻¹ PDB, pH 4.2, 22°C, 22 days) and C04 (2.4 g L⁻¹ PDB, pH 6.2, 13°C, 7 days). Overall, our results suggest great properties of several Trichoderma isolates for future development as biocontrol products.