Exploring the potential of biological control agents in controlling ganoderma - an in vitro and in vivo investigation

Ganoderma boninense is an important fungal pathogen of the oil palm (Elaeis guineensis Jacq.) that causes serious economic losses in the Southeast Asia region. The disease known as basal stem rot or BSR has yet to have an effective control measure to efficiently control this disease. The disease is classified as a soil borne disease and symptoms of infection is almost always observed when it's too late to save the palm. This study attempts to explore the efficacy of two endophytic microbial applications to control the disease both in the lab, nursery and field. Two endophytic microorganisms; Arbuscular Mycorrhizal Fungi (AMF) and endophytic bacteria were tested in combination to control the disease. Glomus intraradices and G. clarum represents the AMF while Pseudomonas strain UPMP3 and Burkholderia strain UPMB3 represents the endophytic bacteria group. In vitro compatibility between these microbes was found to be very promising. The endophytic bacteria are classified as Mycorrhiza Helper Bacteria (MHB) based on the findings through the in vitro assessment. The study further investigates the application of these endophytic microorganisms in the nursery and field conditions. Vegetative assessments in nursery found to be promising for the oil palm seedlings treated with a single application of G. intraradices (T2), followed closely by seedlings treated with both AMF species with UPMP3 (T4). However, when the treatments were repeated in field using the seedling baiting technique, combination of AMF species and UPMP3 treated seedlings gave the highest vegetative parameter assessments. Disease assessment in nursery and field found treatment with both AMF and UPMP3 (T4) to be the best in suppressing BSR disease based on disease severity assessment. These results also indicate that the response of the rhizosphere populations to AMF cannot be generalized and not dependent on the host growth responses to the AMF species but possible to the microbial diversity within the rhizosphere suggesting different AMF may have different effect on the oil palm growth depending on the environment. Nevertheless the study provides an innovative approach for a prophylactic treatment in reducing or delaying the onset of the BSR disease by exploring the potentials of these endophytic microoganisms.