Isolation of fluorescent pseudomonads from the rhizosphere of banana plants antagonistic towards root necrosing fungi

Total aerobic bacteria and fluorescent pseudomonads were counted in bulk an d rhizospheric soils of banana plants of 14 plantations in Martinique (Fren ch West Indies). Fluorescent Pseudomonas isolates were then identified and investigated for in vitro antagonism towards Cylindrocladium sp., a fungal pathogen of banana roots. Total aerobic bacteria and fluorescent pseudomona ds were significantly more abundant in rhizospheric soils than in bulk soil s. Among 58 fluorescent Pseudomonas isolates, 41 were identified as Pseudom onas fluorescens biovar V and 17 as Ps. putida biovar A. Six strains exhibi ted an antagonism towards Cylindrocladium isolates. Among them, Ps. putida strain 93.1 totally blocked fungal growth. No relationship was established between the antifungal effect and enzyme or hydrogen cyanide production by bacteria, suggesting that siderophores and other compounds were involved in fungal inhibition. Antagonistic fluorescent pseudomonads represent a poten tial for the biological control of banana root infections by Cylindrocladiu m sp.