Biocontrol potential of Siminovitchia fortis GURL-96 and Priestia megaterium GURL-107 against rubber leaf fall disease

Leaf fall disease (LFD) has recently emerged as a serious threat to natural rubber production in Southeast Asia, driven by increasingly frequent and severe outbreaks caused by fungal pathogens belonging to the Pestalotiopsis group and related genera such as Neopestalotiopsis, Pseudopestalotiopsis , and Colletotrichum . To identify effective biocontrol agents (BCAs) against LFD, we isolated more than 200 heat-tolerant, Gram-positive endophytic bacteria from rubber leaves and screened 170 isolates for their ability to suppress disease symptoms caused by Japanese Neopestalotiopsis sp. and Colletotrichum siamense using a detached-leaf assay in Japan. Two strains, GURL-96 and GURL-107, consistently inhibited necrotic lesion development induced by both fungal pathogens. Whole-genome sequencing identified GURL-96 as Siminovitchia fortis and GURL-107 as Priestia megaterium . Under greenhouse conditions in Indonesia, both strains showed significant biocontrol efficacy against Indonesian Neopestalotiopsis sp. on seedlings of three of the four tested rubber clones. Moreover, field trials conducted in Palembang, Indonesia, revealed that GURL-96 and GURL-107 reduced LFD severity by an average of 15% and 11%, respectively, on young trees of the susceptible GT-1 clone. These findings highlight the promise of GURL-96 and GURL-107 as BCAs for managing rubber LFD. Both strains suppressed pathogen spore germination on rubber leaves and restricted mycelial growth through antibiosis mediated by diffusible metabolites and volatile compounds, indicating that direct inhibition contributes to their biocontrol performance. To our knowledge, this is the first report demonstrating the biocontrol potential of S. fortis and P. megaterium against rubber LFD.