Pathological investigation and morpho-molecular characterisation of Lasiodiplodia theobromae causing fruit rot diseases on Hydnocarpus longipedunculatus – A novel host record from India

Abstract

Hydnocarpus longipedunculatus, a medically significant tree species, is threatened and has a narrow distribution, being endemic to the Southern Western Ghats of India. A case of fruit rot disease was observed in a solitary tree of H. longipedunculatus in the Kulamavu forest areas of Kerala, India. The causative fungus, Lasiodiplodia theobromae, was isolated and identified through a combination of morpho-cultural characteristics and molecular sequence analysis involving the internal transcribed spacer (ITS), partial translation elongation factor-1-α (TEF1-α), partial β-tubulin (TUB2), and large subunit ribosomal ribonucleic acid (LSU) regions. Additionally, concatenated multigene (ITS-TEF1-α-TUB2) phylogenetic analysis was done. Pathogenicity tests were conducted in vitro using mycelial disc methods and confirmed the pathogenic nature of the fungus through re-isolation and morphocultural analysis, satisfying Koch's postulates. Previous studies neither have reported H. longipedunculatus as a host for L. theobromae, nor has any genus within Hydnocarpus. Therefore, this represents the first documented instance of H. longipedunculatus as a novel host record for L. theobromae from India.