Materials and Methods Sources of Trichoderma sppSlants of six species of Trichoderma (T. harzianum NBAII Th 1; T. viride NBAII Tv 23; T. virens NBAII Tvs 12; T. koningi MTCC 796; T. pseudokoningi MTCC 2048; T. hamatum NBAII Tha-1.) were obtained either from IARI, New delhi or from MTCC, Chandigarh. One local isolate of T. harzianum was also collected from culture collection of Department of Plant Pathology, Junagadh Agricultural University, Junagadh. Isolation of phytopathogenic fungiMacrophomina phaseolina (Tassi) Goid was used as pathogen. The castor plants showing typical symptoms of root rot were collected AbstractIn vitro potentialities of seven species of Trichoderma were evaluated against phytopathogen Macrophomina phaseolina by dual culture techniques. The maximum growth inhibition of test pathogen was observed by antagonist T. koningi MTCC 796 (T4) (74.3%) followed by T. harzianum NABII Th 1 (T1) (61.4%) at 7 days after inoculation (DAI). Further, mycoparasitism of antagonists were observed upto 14 DAI. Pattern of growth inhibition of test fungus was continued with maximum 14.7% increases in T4 (85.2%) followed by 6.8% elevation in T1 (65.6%) antagonists during 7 to 14 DAI. Microscopic study showed that these two antagonists were capable of overgrowing and degrading M. phaseolina mycelia, coiling around the hyphae with apressoria and hook-like structures. At 14 DAI, T. koningi MTCC 796 completely destroyed the host and sporulated. The specific activities of cell wall degrading enzymes-chitinase, β-1, 3 glucanase, protease and cellulase were tested during different incubation period (24, 48, 72 and 96 h) when Trichoderma spp. grew in presence of pathogen cell wall in synthetic media. The antagonist T. koningi MTCC 796 induced higher chitinase and protease activity at 24 h incubation while β-1, 3 glucanase activities was elevated 1.18 fold during 72 to 96 h. Total phenol was produced significantly higher in culture supernatant of T. koningi MTCC 796 antagonist followed by T. hamatum NBAII Tha 1 and T. harzianum NBAII Th 1 at 48 h incubation. The growth inhibitions of pathogen during antagonism was positively correlated with coiling pattern of antagonists at 14 DAI, and induction of chitinase, β-1, 3 glucanase and total phenol content.