Isolation and Functional Characterization of Margalitia shackletonii and Bacillus subtilis from Biofertilizer with Strong Antagonistic Activity Against Ganoderma boninense

Basal stem rot (BSR), caused by Ganoderma boninense, is a major threat to oil palm plantations, leading to severe yield losses and significant economic impact. Early detection of BSR remains challenging because of the delayed onset of symptoms, while monoculture practices further exacerbate disease prevalence. G. boninense, a white rot fungus, invades root and vascular tissues of oil palm, impairing water and nutrient transport, ultimately causing plant decay and death. This study aimed to isolate, characterize, and identify bacterial isolates with both anti-Ganoderma and plant growth-promoting (PGP) abilities from a commercial biofertilizer, CRPO, specifically formulated for oil palm cultivations. Two isolates, K3 (Margalitia shackletonii) and K8 (Bacillus subtilis) displayed strong antagonistic activity against G. boninense, with percentage inhibition of radial growth (PIRG) values exceeding 89%. For PGP traits, K3 demonstrated broad potential, including phosphate and potassium solubilization, nitrogen fixation, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, siderophore and high indole-3-acetic acid production. In contrast, K8 displayed positive results only for nitrogen fixation and ACC deaminase production. The dual functions of these isolates in suppressing G. boninense while enhancing plant growth confirms their presence as biocontrol agents. These advance sustainable BSR management strategies by reducing reliance on chemical inputs and strengthening oil palm resilience.