Black Sigatoka disease caused by the fungus Mycosphaerella fijiensis Morelet is the most devastating disease
of bananas worldwide. Its management is reliant on protectant and systemic fungicides despite their
environmental concerns. This study evaluated the effect of a microbial fungicide (MF) based on Bacillus
subtilis EA-CB0015 and its metabolites for the control of black Sigatoka disease on banana plants in greenhouse
and field conditions. The MF applied at 1.5 L/ha and 3.0 L/ha provided control of the disease comparable
to the protectant fungicide chlorothalonil in greenhouse. In the field, the MF applied in solution
with water at 0.15 L/ha and 1.5 L/ha every 11 days during 10 weeks reduced black Sigatoka disease severity
in 20.2% and 28.1% respectively; reductions comparable to those obtained with the protectant fungicides
chlorothalonil (1.5 L/ha) and mancozeb (3.8 L/ha). The MF incorporated into different programs
with systemic fungicides reduced disease level up to 42.9% with no significant differences with the conventional
program. To determine which component of the MF is responsible for the activity against M.
fijiensis, greenhouse and in vitro tests were set up to evaluate individually the spores, vegetative cells
and secondary metabolites of B. subtilis EA-CB0015. All components reduced the severity of the disease
and the germination of ascospores. For both trials the activity of the metabolites was higher and comparable
to the activity obtained with the MF, indicating that the efficacy of the MF depends mainly on the
metabolites and in lesser extent to B. subtilis EA-CB0015 cells.