Unveiling two new species of Ganoderma (Ganodermataceae, Basidiomycota) causing basal stem rot on oil palm from India.

Ganoderma is a major fungal pathogen causing basal stem rot (BSR) in oil palm, leading to significant yield losses. Owing to high morphological plasticity and complex speciation within the genus, traditional taxonomic approaches have often been insufficient for accurate species identification. Notwithstanding the global diversity of Ganoderma, the species identity and delimitation of the pathogen causing BSR in oil palm in India remain unresolved. In this study, BSR-associated Ganoderma isolates were investigated using an integrated approach combining macro- and micro-morphological characterization, pathogenicity assays, aggressiveness profiling, laccase activity evaluation, and multi-locus sequence analysis (ITS, rpb2, and tef1-α). Multi-locus phylogenetic analyses of individual and concatenated datasets resolved the isolates into two well-supported, distinct clades representing two novel taxa. Ganoderma pseudombrekobenum sp. nov formed a strongly supported sister lineage to G. mbrekobenum, whereas Ganoderma indica sp. nov formed a distinct lineage within the G. orbiforme species complex and was supported by morphological and molecular evidence. These findings reveal high Ganoderma diversity and taxonomic complexity in oil palm BSR in India, highlighting the need for accurate species-level identification.