Screening potential biological control agents and efficacy of mixed-microorganisms in controlling oil palm basal stem rot caused by ganoderma boninense

Single application of biological control agent may prove to be an effective agent for suppressing basal stem rot (BSR) disease in oil palm. However, in nature, there are numerous organisms that may have antagonistic behavior to a particular pathogen existing in the same space and interacting to each other. The main objective of this study was to investigate the effectiveness of mixed antagonists inocula against the palm fungal pathogen, Ganoderma boninense. A total of 803 microbes were obtained from freshly isolated of various substrates and 197 isolates from UNIMAS culture collection. They were screened for their antagonistic activities against G. boninense. Results from the screening tests showed that 233 of the isolates were able to inhibit the growth of the pathogen in four different interactions; formation of inhibition zone, partial mutual intermingling, mutual intermingling and inhibition at contact point. Some changes in characteristics of mycelia and hyphae of pathogen were seen depending on the type of interaction with the antagonist for instance changes in mycelial color from white to dark brown and the hyphae became shrunken, distorted, reduction of cytoplasm content and the tips were blunted, swollen and some were curly. Fifteen selected isolates forming zone of inhibition were formulated into five mixed antagonists inocula against the G. boninense. The mixture that resulted highest percentage of reduction of the colony radial growth of the pathogen was selected for further study on their compatibility and for in situ. The mixed antagonists inocula comprised of Penicillium citrinum, Penicillium pinophilum and Burkholderia gladioli produced the highest zone of inhibition up to 61.89%. These three isolates showed compatibility since they were able to grow together. Oil palm seedlings were treated with two different concentrations of the mixed antagonists inoculums, 2.7 x 107 spores/ml (T2) and 2.7 x 1014 spores/ml (T3). Seedlings without infected, (T0) or infected with the pathogen but not treated with the antagonists, (T1) were used as the control experiment. In in situ tests, T2 and T3 seedlings were successfully inhibiting the growth of the G. boninense when observed after 5 months of application. Based on disease severity index (DSI), root dry weight and chlorophyll content, there was no significant different (p=0.05) between T2 and T3 seedlings. However, there was significant different, (p