Taxonomical and functional characterization of Bacillus strains isolated from tomato plants and their biocontrol activity against races 1, 2 and 3 of Fusarium oxysporum f. sp Lycopersici

Fusarium wilt is an economically important disease of tomato crops (Solanum lycopersicum L.) grown in Brazil that can reduce tomato yield. Among the alternative approaches for controlling this fungal disease, application of antagonistic bacteria has recently been increasing. This study aimed to select and identify phylogenetically bacteria belonging to the genus Bacillus that have antagonistic activity toward three races of the fungus Fusarium oxysporum f. sp. lycopersici (Fol) that colonizes tomato plants grown in infested areas and cause fusarium wilt. The 16S rRNA subunit sequences of 32 bacterial strains isolated from 20 healthy tomato plants showed high diversity and many had high similarity to species of the genus Bacillus: B. toyonensis, B. cereus, B. aryabhattai, B. megaterium, B. aerius, B. stratosphericus and Paenibacillus barcinonensis. In vitro antagonism tests showed that some bacterial strains reduced mycelial growth of the three fungal races in a dual method. Among the four tomato genotypes tested, the Perinha Agua Branca variety was the most susceptible to all three fungal races (highest percentage of vascular infection) and was used for a greenhouse experiment to evaluate the antagonistic role of Bacillus strains against fungal pathogens. The B. cereus strain controlled 100% of the damage caused by the race 1 isolate, whereas strains from species B. megaterium controlled 100% the damage caused by the race 2 isolate. B. toyonensis controlled 100% of disease caused by race 2 and race 3 isolates. Among the bacterial strains tested, 82% and 94% had proteolytic and cellulolytic activity, respectively. Together the results suggest that some Bacillus strains could control fusarium wilt in tomatoes caused by Fol race 1, 2 and 3. In addition, these strains have functional activities that may improve growth of tomato plants.