Biocontrol Delivery System of Bacillus subtilis and Trichoderma harzianum Formulated with Graphite and Silica Nano Particles to Control Phytophthora infestans in vitro

Abstract

A novel biocontrol delivery system by using graphite was proven effective in controlling bacterial plant pathogens. In this study, a consortium of biocontrol agents, consisting of Bacillus subtilis and Trichoderma harzianum, was formulated in graphite added with silica nano particles (NPs). B. subtilis is an endophytic bacterium, while T. harzianum is a rhizosphere fungus. The formulation was in vitro tested on Phytophthora infestans, the cause of leaf blight on tomatoes. The objective of the experiment was to study the ability of single and consortium of B. subtilis and T. harzianum, formulated in graphite and silica NPs, in inhibiting the in vitro growth of P. infestans compared to the non-formulated ones. The experimental design was the randomized complete block design comprised of eight treatments and replicated four timens. The eight treatments were dual cultures of the consortium and the pathogen on V-8 medium as follow: B. subtilis only, B. subtilis + graphite + silica NPs, T. harzianum only, T. harzianum + graphite + silica NPs, B. subtilis + T. harzianum, B. subtilis + T. harzianum + graphite + silica NPs, graphite + silica NPs, and a control. It was concluded that the abilities of both single and consortium of B. subtilis and T. harzianum, formulated with graphite and silica NPs, in inhibiting the in vitro growth of P. infestans were the same as the nonformulated ones. This proved that the formulation in graphite added with silica NPs in the biocontrol delivery system did not reduce the ability of the biocontrol agents to control P. infestans in vitro. The pathogen growth inhibitions caused by the single and consortium of B. subtilis and T. harzianum formulated with graphite and silica NPs were ranged from 35 -54%, compared to the non-formulated ones 24.19 -49.48%.