Revision of Ganoderma species associated with stem rot of coconut palm

Stem rot by Ganoderma is a disease of major concern for coconut farmers. Many species (G. applanatum, G. boninense, G. lucidum, G. zonatum) have been implicated as the causal agents of the disease. Despite its importance, systematics of the rot-associated Ganoderma remains uncertain and unresolved. Morphologically heterogeneous basidiomata of the putative pathogen(s) from infected palms in multiple disease sites were collected during an outbreak in the coastal state of India, Kerala. Morphological and molecular investigations revealed that these specimens were distinct from all the Ganoderma species so far identified and reported from coconut. Although with a close morphological resemblance to many Ganoderma species collected from palms, they exhibited unique genetics and geographic distribution patterns. We present a taxonomic reassessment of the species collected from infected coconut palms in India and also propose two new species, Ganoderma keralense and G. pseudoapplanatum. A taxonomic key to Ganoderma species on palms is given.