Efficacy of Trichoderma spp. consortium as potential biocontrol agents of Ganoderma disease of oil palm, and involvement of antioxidant enzymes and total phenolic content

Oil palm (Elaeis guineensis) is an economically important cash crop, grown primarily for its oil and has become one of the main oil crop in the world. Unfortunately, a major constrain faced by oil palm industry particularly in Malaysia and Indonesia is the devastating disease known as Ganoderma disease caused by Ganoderma spp. To date, this disease has been causing considerable oil palm yield losses and collapse of oil palm trees, consequently affecting its contribution to the producer’s economy. Thus, research on sustainable and eco-friendly remedy to counter Ganoderma disease is on the upsurge to avoid the current control measures via synthetic fungicides. Trichoderma spp. have been the most studied and valued microbes as biological control agents in an effort to combat a wide range of plant diseases sustainably. In addition, knowledge on Trichoderma’s mechanism employed to act as biological control agent, could be useful in improving on their ability as potent biological control agents against Ganoderma spp. Therefore, in this current study, the potential of Trichoderma spp.(Trichoderma asperellum, Trichoderma harzianum, and Trichoderma virens) as a consortium approach was evaluated as biological control agents against Ganoderma disease on oil palm with these objectives: i) To characterize and identify the selected Trichoderma spp. via morphological and molecular characterization, ii) To evaluate their bio-inoculant potential as oil palm seedling treatment for the control of Ganoderma disease and iii) To study the effects on vegetative growth and suppression of Ganoderma boninense infection in oil palm seedlings treated with Trichoderma spp. as single or consortium application. Prior to in vitro assessment, all Trichoderma isolates studied were subjected to morphological and molecular identification. Antagonistic effects of Trichoderma spp. against G. boninense growth evaluated via dual culture test and culture filtrate test. The results demonstrated that the percentage inhibition of radial growth (PIRG) of G. boninense was of >75% in both in-vitro assays. In addition, ability of Trichoderma spp. in producing fungal cell wall degrading enzymes such as chitinase, glucanase, β-1, 3-glucanases and protease were also assessed. All the isolates studied demonstrated potential for the production of cell wall degrading enzymes. However, to measure the potential in Ganoderma disease suppression and enhancement of vegetative growth, an in-vivo trial of six months duration was conducted on oil palm seedlings via G. boninense artificial inoculation treated with single species and consortium of Trichoderma spp. in a nursery condition. The consortium of Trichoderma spp. applied found to be the most effective treatment in suppressing Ganoderma disease with 83.03% and 89.16% from the foliar and bole symptoms respectively. Besides that, the consortium application of Trichoderma spp. exhibited tremendous enhancement in the oil palm seedling vegetative growth parameters such as plant height, stem girth, leaf area, frond count, shoot and root (fresh and dried weight) with significant difference at P<0.05 compared to all other treatments designed. Nevertheless, to further confirm the ability of Trichoderma spp. as an excellent biological control agent in a consortium approach via in vivo study, involvement of antioxidant enzymes [peroxidase (PO) and polyphenol oxidase (PPO)] and total phenolic content (TPC) of treated oil palm roots were measured. The results obtained demonstrated, highly induced significant activity of PO, PPO and TPC was recorded in the consortium treatment compared to the control treatment. Disease development was slower in the seedlings treated with consortium of Trichoderma spp. compared to the positive control, which exhibited with the highest percentage of disease severity. Therefore, the consortium application of Trichoderma spp. to the oil palm seedling roots before transplant (at nursery stage) could provide a promising sustainable approach for the management of Ganoderma disease of oil palm. Despite this, there is a need for further study in evaluating the biological control potential as consortium approach of Trichoderma spp. under field conditions.

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