Abstract

Oil palm is major commodity crop in Malaysia and Indonesia and attributes to 30% of the global edible oil market. Basal stem rot (BSR) disease is a white rot disease that damages lower stem and bole of oil palm trees during their economic life. The causal agent, a hymenomycete fungi, Ganoderma boninense has been identified as the most virulent pathogen for BSR and to date, there has been no successful measures to control this disease. Integrated approach to disease control requires a robust diagnostics system coupled with a curative agent. In this study, chitosan, a natural polymer from deacetylated chitin of crab and shrimp shells (ranging between 0 and 2% w/v), induced defense responses in oil palm both in vitro (axenic) and in vivo (non-axenic) diagnostic screenings. In vitro infections has higher total phenolic concentration (p<0.05) associated with 0.50% and 1.00% chitosan while in control, significant (p<0.05) lower fresh weight and browning effects were detected. The phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), and peroxidase (POD) assays show that 0.50% chitosan gives higher enzyme activity as compared to control after 35 days of treatment. In vivo experiments of young oil palm showed that soil drenching application at 0.5 % concentration of chitosan was the most appropriate delivery method with the lowest disease severity index in 9 months post

infections. Besides, multiple application of 3 times (T5) had the best results of 55.4% disease reduction and lowest bole infections at 20.8%. Plants were observed to have significant positive results in mean height (35 cm), stem diameter (0.8 mm), root mass (90 g) and fresh weight (180 g) when chitosan was successfully amended in potting mix. These results demonstrates that chitosan induces defense response in oil palm to counter BSR infections.