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The present study has been undertaken to determine the efficacy of some antagonistic fungi isolated from the rhizosphere of wheat plants grown in Summer region, Diwaniya Governorate, Mid Iraq for the biological control of Helminthosporium sativum, the causal organism of root rot disease of wheat in vitro. Three different species from the genus Trichoderma: T. harzianum, T. pseudokoningii and T. lignorum, in addition to Stachybotrys atra and Penicillium sp. were isolated from the rhizosphere of wheat plants. Laboratory experiments indicated that T. harzianum and S. atra were highly antagonistic to the pathogen when grown together on potato dextrose agar in Petri plates. Microscopic examination of the mycelia showed that hyphae of T. harzianum were parasitized H. sativum, coiled around its hyphae and caused its lysis, but did not penetrate inside the hyphae. However, S. atra was invaded colonies of H. sativum and caused severe hyphal damage. In the experiments of culture filtrates of the antagonistic fungi, T. harzianum and S. atra, were able to suppress growth of H. sativum, if incorporated in the medium and proved to be effective in controlling the pathogen. Results of effect of filtrate on spore germination showed that about 80 and 95% of them are unable to germinate with high concentrations (15 or 20 %) of culture filtrates of T. harzianum and S. atra respectively. However, the other antagonists: T. pseudokoningii, T. lignorum and Penicillium sp. were less effective in inhibiting spore germination of the pathogen. Results of antagonistic effect of the culture filtrates on wheat seed infection, except T. lignorum, showed that seed colonization by the root rot fungus was decreased significantly at the concentrations of 15 and 20 % compared with control. Seed coating with antagonistic fungi was the best biological seed treatment for reducing seed rot and diseased seedling caused by H. sativum. Antagonistic fungi have no side effects on seed germination except Penicillium sp. which reduced the seed activity and germination as compared with the other antagonists and with the control. It can be concluded that T. harzianum is a strong mycoparasite and S. atra is a good antagonistic agent to control H. sativum, but in fields may be their activity are conditioned by soil environment specially the microflora.

Biological control of Helminthosporium sativum the causal agent of root rot in wheat by some antagonistic fungi