The invention relates to a biofungicidal composition from a biologically pure culture of a Chilean bacterial isolate obtained from grape skin corresponding to Serratia plymuthica CCGG2742, to be used as an environmentally-friendly biological control agent for controlling fungal plant diseases, especially fruit susceptible to infection by Botrytis cinerea, efficiently inhibiting the germination of conidia and the proliferation of the mycelium of said phytopathogenic fungi. Said biofungicidal composition also protects the leaves of plants and fruit from infection by said fungus, and can potentially be used in the biological control of other phytopathogenic fungi and micro-organisms.