A Rhizobacterium Kitasatospora nipponensis Demonstrates Antifungal Activity against Basal Stem Rot Disease and Promotes Plant Growth in Oil Palm (Elaeis guineensis) Seedlings

Basal stem rot (BSR), caused by Ganoderma boninense, is a severe disease affecting oil palm plantations. The excessive use of synthetic fungicides to control BSR poses risks to human health and the environment. Biological control using the rhizobacterium Kitasatospora nipponensis is considered an environmentally friendly and effective method to address this problem. This study evaluated the biocontrol potential of K. nipponensis KM6-4 against G. boninense and its ability to promote oil palm seedling growth. In vitro, assays demonstrated significant antifungal activity, with 75.44%, 70.00%, and 21.42% inhibition rates in dual culture, volatile antifungal bioassay, and agar well diffusion methods, respectively. K. nipponensis KM6-4 exhibited higher cell wall-degrading enzyme activity in cell-free culture filtrate (CF) compared to the control. Boiled sorghum and organic fertilizer media supported the highest bacterial population (1.2 × 107 CFU/g). In vivo tests showed that K. nipponensis KM6-4 enhanced the growth of oil palm seedlings and reduced BSR severity, achieving a disease reduction of 47.06%. These findings highlight K. nipponensis KM6-4 as an effective and eco-friendly agent for managing BSR and promoting oil palm growth.