Isolation, identification and in vitro characterization of grapevine rhizobacteria to control ochratoxigenic Aspergillus spp. on grapes

Aspergillus spp. are fungal pathogens that attack the grape and that are known for their secretion of mycotoxins, in particular, ochratoxin which is very toxic. A total of 39 bacterial strains isolated from the rhizosphere in Tunisian vineyards were identified using 16S rDNA and rpob gene sequencing: 35 were Bacillus spp. strains, 2 were Brevibacterium spp., 1 was Paenibacillus sp. and 1 strain was Microbacterium oxydans. Biochemical and microbiological screenings revealed that those 39 strains (i) metabolized differently carbon sources, (ii) possessed antibiotic genes and (iii) produced siderophores. Based on their PGP traits, 21 strains were selected and tested in vitro for their antagonistic effect against two fungal pathogens, Aspergillus ochraceus and A. carbonarius. All the tested antagonists were able to reduce the growth of A. ochraceus, with Bacillus amyloliquefaciens being the most efficient; and A. carbonarius, in particular Bacillus pumilus. In vitro screening using detached berries showed the potential of B. pumilus strain G3AX for inhibiting contaminations by Aspergillus spp., that are OTA-producing fungi. At the berry surface, the efficacy of the bacterial strains strongly depended on the presence or absence of wounds.