Fusarium oxysporum f.sp. lycopersici (FOL) is a soil borne pathogen causing wilting occasionally accompanied with severe yield loss in tomato. Biological control of Fusarium wilt diseases is an alternative disease management strategy. In this research, Antagonistic effects of 9 isolates of Pseudomonas fluorescent, Bacillus subtilis and Serratia marcescens were tested in vitro and in vivo against Fusarium wilt of tomato. Antagonistic test between bacteria and pathogen in vitro were tested on King's medium B (KB) and Potato dextrose agar against FOL. Colony area was recorded, compared with control and percentage inhibition of growth was calculated. In greenhouse experiments, root of 3-week-old tomato plants were cut and dipped in bacterial suspension with a concentration of 106 CFU/ml for 30 min. Seven days later, tomato roots plants recut and dipped in conidial suspension of FOL with a concentration of 106 spores/mi. Disease severity was assessed 4 weeks after inoculation by determining the leaf disease index, plant height and vascular discoloration. The experiment was carried out in a completely randomized design in pots under greenhouse conditions and treatments were analyzed by the program MST A TC. The P. fluorescent was reisolated from tomato stems after seven days in a concentration of 104 CFU/ gr fresh weight. In vitro, percentage of growth inhibition varied significantly among the antagonistic isolates and ranged from 20 to 60%. Isolates W34, CW2, 14 and WB 1 of P. fluorescent showed antagonistic effects in vitro and in vivo against FOL. The results obtained indicated that four selected isolates of P. fluorescent were capable to reduce severity of disease with an efficiency ranging from 2 to 8 times and stimulate plant growth up to 3 times in comparison with infected control, whereas isolates of B. subti/is and S. marcescens were not consistently effective.
