Biological control ofSclerotium rolfsiibyTrichoderma harzianumin sugarbeet∗

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Abstract
An isolate of Trichoderma harzianum (IMI no. 238493) directly attacked and lysed the mycelium and sclerotia of Sclerotium rolfsii when the two fungi were grown in dual culture. The type of interactions between the antagonist and pathogen were hyphal coiling, entry through haustoria‐like structure and direct entry in the hyphae and sclerotia of S. rolfsii, the host fungus. In a glasshouse experiment, T. harzianum applied in the form of sorghum culture to 5. rolfsii infested soil gave as high as 76 and 88% disease control in first and second growth cycle of sugarbeet seedlings respectively. The degree of disease control obtained increased with the increase in the amount of T. harzianum applied. This isolate of T. harzianum was found tolerant to PCNB (Pentachloronitrobenzene) in vitro. PCNB at low concentration when integrated with T. harzianum improved disease control. Under field conditions, integration of PCNB and T. harzianum significantly reduced the incidence of Sclerotium root rot (76% disease control) and increased the root, green foliage and sucrose yield per ha.