Antagonistic bacteria against Fusarium spp. isolated from sclerotia of Claviceps gigantea in maize (Zea mays)

Fungal sclerotia house native bacterial populations of interest for biological control of plant pathogenic fungi. The objectives of this research were: i) to explore the bacterial populations associated with Claviceps gigantea sclerotia in maize from six locations in the State of Mexico, ii) to evaluate the in vitro antagonism of these bacterial populations against three species of Fusarium phytopathogens of maize, iii) to molecularly identify the more efficient antagonists and characterize the in vitro production of metabolites. Bacterial populations in the sclerotia were calculated by direct plate count; in vitro antagonism against Fusarium graminearum, F. sublgutinans, and F. verticillioides was evaluated by confrontation in Waksman agar medium. Antagonistic bacteria were identified by partial sequencing of 16S rRNA gene and evaluated in vitro for the production of indole-3 acetic acid, siderophores, lipolytic and proteolytic activity, and mineral phosphate solubilization. The bacterial density ranged from 2.023 to 2.397 Log10UFC g-1 of sclerotia. Twenty-two strains showed in vitro antagonism against at least one Fusarium species and were identified as members of the genera Bacillus, Delftia, Micromonospora, Pseudomonas, Sphingobacterium, Staphylococcus, and Stenotrophomonas. The 22 antagonists showed in vitro lipolytic, proteolytic, siderophore-producing and phosphate-solubilizing activity; only 12 (55%) produced indole-3-acetic acid. Bacillus subtilis (BA1), Pseudomonas syringae (BA2), and Bacillus amyloliquefaciens (BA18) strains were antagonists against the three Fusarium species and produced all the metabolites evaluated.