Effect of Trichoderma asperellum and Bacillus cereus consortium on plant growth and resistance of infected Ganoderma boninense oil palm seedlings

Despite the enormous economic contribution to Malaysia, oil palm industry is facing devastating threats from serious diseases primarily basal stem rot (BSR) disease. Excessive application of chemicals to control BSR may render negative impacts on the biodiversity and subsequently to the human population. Therefore, biological control would be an ideal alternative as a preventive or curative method of BSR. Thus, an insight of biological control effects in vitro and in vivo would be crucial in selecting potential biological control agents (BCAs) to counter BSR disease in a sustainable manner. Plant growth-promoting traits of Bacillus cereus and Trichoderma asperellum such as indole acetic acid (IAA), siderophore production and phosphate solubilization ability were tested. Sealed plate method was conducted to determine the antifungal effects of microbial volatile organic compounds (MVOCs) produced by the BCAs on the growth of Ganoderma boninense. An array of treatments was designed to evaluate the potential of BCAs as single and mixture application in in vivo nursery trial for six months. Plant height and chlorophyll content were recorded on monthly basis to analyze the vegetative growth of the inoculated seedlings. Data on the vegetative growth were subjected to ANOVA for mean comparison by using SAS software. Induction of oil palm enzymes, phenolic content and metabolites in BSR diseased seedlings in response to the designed treatments were assessed. The ability to solubilize precipitated phosphate and produce siderophore were positively exhibited by T. asperellum. Nevertheless, both T. asperellum and B. cereus were able to produce IAA. Sealed plate method demonstrated MVOCs emitted by B. cereus, effectively inhibited G. boninense mycelial growth with the mean of 51.3 mm compared to the control plates (85.0 mm). In the in vivo trial, T. asperellum contributed significantly on the growth of aerial parts while B. cereus on the growth of oil palm roots. In addition, the seedlings treated with T. asperellum demonstrated the highest disease reduction (DR) (57.2%). Different BCA treatments gave different results on oil palm enzymes, phenolic content and metabolites produced by seedlings. However, one similarity could be observed in peroxidase assay, lignin assay and phenolic content where Ganoderma- infected seedlings treated with B. cereus (treatment BG) gave high value in all assays conducted. Gas Chromatography-Mass Spectrometry (GC-MS) analysis showed that phenol, 4-2-aminoethyl- was the most abundant metabolite detected in the mixture treatment of B. cereus and T. asperellum (treatment BT), followed by acetic acid in the treatment BG. Nevertheless, both microbes demonstrated huge potential as BCAs in BSR disease reduction.

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