"In vitro" antagonism of a grapevine endophytic bacillus subtilis strain towards "esca" fungi

Abstract

Preliminary investigations on grapevines (CV Catarratto) with symptoms of “esca” permitted to isolate only bacterial colonies, from black punctuations belonging to the genus Bacillus. Particularly, an isolate was Gram-positive with spore forming and, on the basis of the partial 16S rRNA sequence comparison, it showed a similarity of 99% with Bacillus subtilis subsp. subtilis. There are numerous reports on the antagonistic activity of the species towards several phytopathogenic microorganisms. For this reason the possible bacterial control against the “esca” fungi (Phaeoacre- monium aleophilum, PAL; Phaemoniella clamidospora, PCH; Fomitiporia mediterranea, FOMED), was studied. The antagonistic activity was investigated in vitro by: a) direct method by dual-culture in Petri dishes containing malt extract agar; b) indirect method by adding to fungal growth media cultural filtrate or crude extract bacterial in different concentrations. The results showed that B. subtitles isolate has a powerful antagonistic effect towards all fungal pathogens tested, reducing their growth until 80% (direct method). Moreover, the FOMED growth was reduced at least of 50% with indirect method, while the influence of this bacterial isolate on PCH and PAL growth by indirect method is in progress. As far as we know, this is the first study reporting Bacillus as “natural limiter” of “escape” fungi.