Complexity of Trichoderma-Fusarium interaction and manifestation of biological control

Several Trichoderma isolates were screened for their biocontrol activity against Fusarium oxysporum f.sp. pisi. Eighteen of these isolates (T1 to T18) showed considerable biocontrol potential and were taken further in the study. Initial counter inhibition was observed in all the eighteen dual culture sets where Trichoderma and Fusarium both posed varying degree of inhibition on each other. In three of the sets, Fusarium was found extending narrow outgrowths towards Trichoderma. Trichoderma was later found extending its mycelia along these narrow outgrowths of Fusarium representing a chemo-attractive mechanism of interaction. Finally, parasitic interaction was noticed in all the sets except two. In these two sets, Trichoderma was unable to overcome inhibition posed by Fusarium and, therefore, could not parasitize Fusarium. In the interaction between Trichoderma and Fusarium, the sequence of events noticed was categorized as pre-contact antagonistic interaction, chemo-attractive intermediate phase and, finally, parasitic interaction. Most of the Trichoderma isolates showed considerably good antibiosis and parasitism. Therefore, the primary criterion for selection of the best potential biocontrol agent was poised on the time taken by Trichoderma to complete the sequence of events until parasitism of target pathogen. Among the eighteen isolates of Trichoderma, T. atroviride (Isolate T1) was found to show best activity followed by two isolates of Trichoderma harzianum (Isolate T8 and T11) in terms of time taken to parasitize Fusarium. The present study stresses on quick control on plant disease as a desired quality for popularization of biocontrol agents.