Antagonistic effect of T. harzianum was carried out on F. oxysporum f. sp. lycopersici isolates from UC 82B variety of tomato in a screen house located at the Teaching and Research Farm, Joseph Sarwuan Tarka University, Makurdi, Nigeria during 2015 cropping season to determine their antagonistic effect on the isolates. F. oxysporum isolates tested were coded as: FoAs1, FoAs2, FoAg, FoNb, FoSb, FoAm, FoAk, FoOr, FoAd and FoUAM together with an uninoculated control. The research was laid out in a 2 x 11 factorial and Completely Randomized Design (CRD) method was adopted and the treatments were each replicated 3 times. The antagonistic was introduced at 3 separate periods (Two days before the pathogen, same time with the pathogen and two days after the pathogen). Laboratory tests results revealed bioactive potency of the antagonist on the isolates of the pathogen. Growth inhibition was significantly higher (P?0.05) when the antagonist was inoculated two days earlier than the arrival of pathogenic isolates. Interaction shows that the antagonist inoculated two days earlier that the pathogen gave better inhibition of all the Fusarium isolates tested except isolates FoAd and FoAg compared with when T. harzianum was inoculated same time and two days after the introduction of F. oxysporum. The antagonist (P?0.05) totally inhibited the growth of isolates FoAg, FoAs1, FoNb, FoOr and FoUAM but not those of FoAd, FoAk, FoAm, FoAs2 and FoSb. It is therefore recommended that T. harzianum be exploited and used in the control of tomato wilt diseases caused by Fusarium oxysporum.

Keywords: Antagonistic, Inhibition, Fusarim oxysporum, Isolates, T. harzianum