Lactic acid bacteria [LAB]: potential for control of Fusarium growth

Lactic Acid Bacteria [LAB] are worldwide known as probiotic microorganisms. One of the most important probiotic feature is their strong activity against a wide range of harmful bacteria/fungi (Gaggìa et al., 2011). Production of organic acids and production of antagonistic compounds are the main mechanisms described nowadays. This work focuses on the in vitro selection of LAB strains isolated from environmental sources against Fusarium genus. Fusarium is a well distributed genus of filamentous fungi affecting plant, animal and human health. In the agricultural field, Fusarium is one of the most important plant pathogenic genera, with a record of devastating infections in various economically important plants. In this study, in vitro antagonistic effects of 18 isolates of Lactobacillus spp. were evaluated against F. oxysporum f. sp. lactucae, agent of tracheofusariosis in Lactuca sativa, F. culmorum and F. graminearum, agents of severe diseases in cereals. Fungal inhibition was performed using spot agar test in a triplicate assay (Magnusson et al., 2003). Overnight cultures of LAB were inoculated as spot on MRS agar plates and allowed to grow at 30°C for 24 h. The plates were then overlaid with 10 ml of PDA containing 104 mould spores/ml. After 48-72 h of aerobic incubation at 25°C, the zone of inhibition was measured. All LAB strains (except one) showed antifungal activity against all Fusarium species (inhibition halo between 23.7- 65.3 mm). The highest halos were obtained against F. graminearum on which 50% of the LAB strains showed a total growth inhibition of the colony. These results are probably related to the high amount of organic acids produced by LAB strains but it can also be hypothesized the presence of antifungal compounds. In vivo application of the most successful LAB strains is foreseen towards wheat and lettuce to confirm in vitro results.