Aberathna, B.D.N.P.2021-10-262021-10-262013UWU/PLT/13/0001http://www.erepo.lib.uwu.ac.lk/bitstream/handle/123456789/7398/PLT%2013%20001-19022021115300.pdf?sequence=1&isAllowed=yTrichoderma is one of the most studied and applied fungal biocontrol agents. Trichoderma species suppress pathogens by using a variety of mechanisms such as antibiosis, direct mycoparasitism and competition for space, nutrients and enzyme substrates. White root disease is a serious root disease caused by Rigidoporus microporus which is spreading fast in rubber plantations of Sri Lanka. In this study a laboratory experiment was carried out to identify whether Trichoderma produce or not toxic metabolites to suppress Rigidoporus microporus. Trichoderma strain 01 with Rigidoporus microporus and Trichoderma strain 02 with Rigidoporus microporus were inoculated into separate Potato Dextrose Broth medium. After 12 days of incubation period culture filtrates were taken with sterile 0.22 micron filter paper. Five concentrations 15%, 30%, 45%, 60% and 75% (v/v) of the culture filtrates were tested using the Poison Food Technique on Rigidoporus microporus with three replicates. There was a significant interaction between Trichoderma spp. and concentration of the culture filtrates (p < 0.05). It showed the highest mean percentage growth inhibition by both strains at 75% concentration and the lowest mean percentage growth inhibition at 15% concentration. The mean percentage of growth inhibition at 75% conceptfation of Trichoderma strain 01 was 71.39% and Trichoderma strain 02 was 71.45%. The mean percentage of growth inhibition at 15% concentration of Trichoderma strain 01 was 41.89% and Trichoderma strain 02 was 13.32%. The culture filtrates amended PDA were autoclaved before the inoculation of the pathogen and the results indicated that Trichoderma strain 01 and Trichoderma strain 02 produce a thermo stable toxic substance (secondary metabolites) to inhibit white root disease causative pathogen Rigidoporus microporus. Higher the concentration of the secondary metabolites, greater was the growth inhibition of the pathogen Rigidoporus microporus. Key words: Trichoderma, Biocontrol, Secondary metabolites, Rigidoporus microporus, Inhibitory effectsenPalm and Latex Technology and Value Addition Degree Programme ( PLT)Thesis