Use of biocontrol agents as potential tools in the management of chestnut blight

Castanea sativa is a widespread and important multi-purpose tree in the Mediterranean area. Recently, intensive infestation of gall wasp decreased the production of chestnut, and makes the plants more susceptible to Cryphonectria parasitica, the causal agent of chestnut blight. Generally, biological control of chestnut blight is through natural spread or artificial release of hypovirulent strains of C. parasitica. However, this approach is not always successful. The aim here was to evaluate alternative approaches for control chestnut blight based on application of antagonistic microorganisms. In-vitro antagonistic activities of fungal species Trichoderma and Penicillium were tested after in vitro isolation from chestnut bark. In dual cultures, these antagonistic fungi consistently reduced growth of C. parasitica. Three commercial formulations based on Trichoderma spp., Glomus spp. and Bacillus subtilis were tested at three doses, both in vitro and directly applied to cuttings of chestnut stems as co-inoculations and as separated inoculations with C. parasitica mycelium plugs. With co-inoculation, B. subtilis showed the best performance against chestnut blight, with necrotic areas reduced by > 70%. In separated inoculations, B. subtilis reduced the size of cankers on chestnut stems, by 29%-67%, as also for Trichoderma spp., by 36%-65%, and Glomus spp., by 31%-63%. Application of commercial formulations based on antagonistic microorganisms are effective tools in management of chestnut blight.