Induction of phenolics and defense-related enzymes in coconut (Cocos nucifera L.) roots treated with biocontrol agents

The effect of soil application of biocontrol agents (Pseudomonas fluorescens, Trichoderma viride and T. harzianum) in combination with chitin on induction of phenolics and defense enzymes in coconut roots infected with Ganoderma lucidum, the causal agent of Ganoderma disease, was investigated. Soil application of these biocontrol formulations in combination with chitin induced a significant increase in the activities of peroxidase (PO), polyphenol oxidase (PPO), phenylalanine ammonia-lyase (PAL), chitinase and β-1,3-glucanase in the G. lucidum infected palms. Activities of both PAL and PO reached maximum levels within 3 d while the activity of PPO reached the maximum level 6 d after application of a mixture of P. fluorescens, T. viride and chitin. Isozyme analysis revealed that unique PO3 and PPO2 isozymes were induced in coconut palms treated with P. fluorescens + T. viride + chitin. Accumulation of phenolics was recorded 3 d after treatment and reached maximum levels 9 d after treatment application. Activity of chitinase was significantly increased from the third day after treatment imposition and continued to increase up to 9 to 12 d in all treatments. Chitinase isozyme analysis revealed that a unique Chit3 isoform was induced in coconut roots treated with P. fluorescens + T. viride + chitin. The β-1,3-glucanase activity was maximum 9 d after treatment application. The mechanisms by which P. fluorescens + T. viride + chitin reduced the incidence of Ganoderma disease in coconut may be related to its ability to induce defense mechanisms in coconut palms.