Fusarium oxysporumfsp. lycopersici (F.O.L) causes Fusarium wilt in tomato and is responsible for important crop losses in fields and commercial green houses. Chemical control of this disease is very difficult, because the causal agent (F.o.fsp. Lycopersici) is a soil-born pathogen, therefore biological control is the best method. In this survey, first in vitro by using dual culture test, antagonistic effect of nonpathogenic isolate of Fusarium on Fusarium wilt of tomato was evaluated to biocontrol of disease. Colony after 4 days were recorded and compared with control and percentage inhibition of growth was calculated. Nonpathogenic Fusarium did not show antagonistic effects in vitro against Fusarium wilt of tomato. In vivo, root of3- week- old tomato plants were cut and dipped in nonpathogenic strain suspension with a concentration of 106 spores/ ml for 30 min. Seven days later the roots of tomato plants were recut and dipped in conidial suspension of Fusarium oxysporum f sp. lycopersici with a concentration of I 06 spores/mi. After 3 weeks plants inoculated with Fusarium oxysporum f sp. lycopersici showed diseases symptoms, whereas plants inoculated with nonpathogenic strain or a mixture of both fungi remained symptoless the duration of the experiment. In another experiment, nonpathogenic Fusarium and the pathogen were separated either physically or in time and diseases symptoms did not show. It is concluded that nonpathogenic Fusarium strain is able to induce resistance against (F.O.L) in tomato plants. This result has important practical implication for biocontrol of tomato diseases under commercial conditions.
