Soil physicochemical properties closely associated with fungal enzymes and plant defense enzymes in Ganoderma-infected oil palm orchards

Abstract

Ganoderma boninense causes basal stem rot disease of oil palm, a serious problem in many countries producing crude palm oil. Ganoderma penetrates host cells by producing cell wall degrading enzymes (CWDEs) and its mycelia trigger defense responses in the host plant. The soil physicochemical properties affect plant growth and soil microbes. Only limited knowledge is available on the relationship between soil characteristics and occurrence of plant diseases. Thus, this study aimed to determine soil physicochemical properties, CWDEs in rhizosphere soil, PR proteins, and defensive enzymes in plant roots, and to look for potential associations in Ganoderma-infected oil palm plantations. Roots and rhizosphere soil were sampled from Ganoderma infected and non- infected oil palms from the main oil palm plantation area in southern Thailand. Spectrophotometry was used to investigate enzyme activities. Fungal laccase, lignin peroxidase (LiP), and manganese peroxidase (MnP) were positively correlated to organic matter (OM) and organic carbon (OC) concentrations, but these enzymes were negatively correlated to soil pH. Cellulase was sensitive to soil physicochemical properties when compared with laccase, LiP, MnP and xylanase. Regarding plant defensive enzymes, high levels of OM, OC, calcium, potassium, manganese, magnesium, nitrogen and zinc in soil were related to chitinase, β-1,3-glucanase, phenylalanine ammonia lyase (PAL), peroxidase (POD) and polyphenol oxidase (PPO) synthesis in oil palms. Moreover, POD, PPO and PAL were positively correlated to fungal laccase, LiP and MnP. Our results indicate that the relationships between fungal enzymes, defense related enzymes in host plant, and soil physicochemical properties, are involved in determining basal stem rot disease occurrence in oil palm.