Antimycotic activity of Bacillus amyloliquefaciens against fungi of vineyards soil origin

Abstract

Preliminary investigations on grapevines (cv Catarratto) with symptoms of “esca” allowed the isolation of different bacterial colonies (Alfonzo et al, 2009). A Gram-positive, spore forming isolate, able to inhibit fungal growth, was subjected to identification. On the basis of the whole 16S rRNA gene sequence, it showed a similarity of 99% with Bacillus amyloliquefaciens. There are numerous reports on the antagonistic activity of this species towards several phytopathogenic microorganisms. For this reason, the potential of the bacterial strain against the fungi commonly associated to the soil of vineyards (Alternaria alternata, Aspergillus ochraceus, Aspergillus carbonarius, Cladosporium cladosporoides, Fusarium oxysporum, Penicillium brevicompactum and Verticillium dahliae) was studied. The antagonistic activity was investigated in vitro by two different protein extracts (CME = Crude Metabolites Extract and CEP = Crude Extract Protein) obtained by different methodologies (McKeen et al, 1986; Wichitra et al, 2008). Antagonistic activity was assayed by the agar-well diffusion and critical dilution assay. One active unit AU ml-1 was defined as the reciprocal of the highest dilution that gave growth inhibition of the fungi species (Villani et al, 1995). The results showed that both CME and CEP have a powerful antagonistic effect towards all fungal organisms tested. In particular, CEP showed greater efficacy than CME. Fungi were less sensitive to the activity of the CEP accordingly to the following order: A. ochraceus (10240 AU ml-1), A. alternata (1920 AU ml-1), A. carbonarius (1280 AU ml-1), V. dahliae (960 AU ml-1), F. oxysporum (800 AU ml-1), P. brevicompactum (600 AU ml-1) and C. cladosporoides (160 AU ml-1). Diversity has been the antibiotic activity of CME: A. alternata (1920 AU ml-1), A. carbonarius (960 AU ml-1), V. dahliae (800 AU ml-1), P. brevicompactum (240 AU ml-1), A. ochraceus (160 AU ml-1) F. oxysporum and C. cladosporoides (120 AU ml-1). Further studies are needed to determine the chemical nature of the active metabolites and to evaluate their potential in biological control programmes.