In vitro antagonistic activity of soil microbes isolated from oil palm to Ganoderma zonatum

Abstract Ganoderma zonatum is the causal agent of basal stem rot of oil palm (Elaeis guineensis Jacq) in Riau. The research objective was to explore and select soil microbial antagonists to Ganoderma zonatum. Soil samples were taken from the non/rhizosphere of 27 oil palm plants in Kampar and Siak Regency, Riau Province, Indonesia, in 2018-2019. The soil microbes were grown on Potatoes Dextrose Agar for fungus and Tryptic Soy Agar for the bacterium. The antagonist was measured by a dual culture method. The colony diameter of G. zonatum the (dual) culture was measured to assess the inhibition potency of the potential microbial antagonists. The soil microbial collected was 138 isolates, including 58 of Trichoderma spp. and 80 of bacteria. The inhibition against the isolated soil microbes to G. zonatum growth ranged from 46-74% for Trichoderma spp. and 0-86% for the bacterium. Seven isolates of Trichoderma spp and 13 of bacterial inhibited G. zonatum growth >70%, have potential as biocontrol agents. Two isolates that showed the most potential as antagonists, i.e Trichoderma harzianum (AC2, rhizosphere) and Burkholderia gladioli (N1, non-rhizosphere) could be developed for further as microbial antagonists.