Indian Phytopath. 59 (3) : 290-293 (2006) Differential efficacy of bioagents against Fusarium udum isolates VISHWA DHAR*, S. MISHRA and R.G. CHAUDHARY Indian Institute of Pulses Research, Kanpur 208 024 ABSTRACT: Efficacy of saprophytically competitive bioagents against Fusarium udum was studied in vitro at the Indian Institute of Pulses Research, Kanpur during 2000-2001 using dual culture technique on potato dextrose agar medium. Three bioagents viz., Trichoderma viride (TNAU, Coimbatore), T. harzianum (GBPUA&T, Pantnagar) and Gliocladium virens (GBPUA&T, Pant Nagar) were evaluated against ten isolates of F.udum obtained from research farm of IIPR, Kanpur. The three bioagents varied in their efficacy in relation to F. udum isolates. After 96 hours of inoculation low colony growth was recorded in F 10 , F 12, F 14 and F 17 isolates (16.6- 18.6 mm) in the presence of T. viride while least growth of F 14 (16.0 mm) was obtained with T. harzianum. The colony growth of F 10 was on par (18.3-19.0 mm) with all three bioagents. T. harzianum was found growing saprophytically fast in the presence of ten F. udum isolates in dual culture. After 96 hrs of incubation, the percent reduction of ten isolates of F. udum ranged between 35.5-54.8 against T. viride, 36.4-54.7 against T. harzianum and 36.4-57.3 against G.virens. Population counts of F.udum isolates and bioagents from the parasitized colonies after 7 days of inoculation using dilution technique revealed at par population in F 13 and F 14 . G. virens recorded highest population in the presence of F 8 while T. viride and G. virens showed at par population in F 10 . Key words : Pigeonpea, Fusarium udum, bioagents, differential efficacy Wilt caused by Fusarium udum Butler is the most important disease of pigeonpea in north, central and south India inflicting heavy losses in yield . Annual crop loss due to this disease in India has been estimated as 97000 tonnes (Kannaiyan et al., 1984). Several methods have been suggested to manage this disease by chemical, seed treatment, soil solarization, inter/mixed cropping or crop rotation with sorghum and through host plant resistance (Vishwa Dhar and Chaudhary, 1998). Although, these options have potential to reduce the disease incidence to some extent, wilt still continues to be one of the major biotic constraints to pigeonpea production. Identification of few potent bioagents against F. udum like species of Trichoderma, Gliocladium and Bacillus have provided impetus for a comprehensive approach towards management of this disease. However, the differential field response of these bioagents in controlling the disease across the locations and over the years has been a cause of concern. In addition to soil and climatic factors,variability in the pathogen might be also responsible for the inconsistent results. The present investigation was therefore, conducted to study the differential reaction of F. udum isolates against bioagents Trichoderma viride, T. harzianum and Gliocladium virens (Syn. Trichoderma virens) in vitro. MATERIALS AND METHODS Ten isolates of F. udum with variable morphological characters and pathogenicity were co-evaluated with three bioagents, T. viride (TNAU, Coimbatore), T. harzianum (GBPUA&T, Pantnagar) and G virens (GBPUA&T, Pantnagar) in vitro using dual culture technique on Potato dextrose agar medium. Twenty ml of medium after sterilization was poured in 90 mm pre-sterilized Petri- plates and allowed to solidify. Discs of 5 mm from 7 days growing culture of each isolate of F. udum were cut using a sterilized metallic cork borer. One disc of *Corresponding author: dr_vishwadhar@yahoo.com