Association of Exserohilum rostratum with ginger: Morphological characterization, phylogenetic relationships and pathogenicity assays

Abstract

Ginger is one of the most commonly consumed dietary spices with significant pharmacological and physiological activities. The occurrence of a distinctive type of leaf blight with characteristic reddish-brown lesions along the leaf margins and distal end of the leaves was observed on ginger in Kerala and Karnataka states in India, The mean percent incidence in the surveyed fields ranged from 0.92–36.02 and 1.58 -77.28% respectively.The isolated fungus produced brown coloured conidiophores with septa and conidia were brown to dark brown, cylindrical with a smooth surface, rounded at both ends, septate, and germinated in a bipolar fashion.The molecular phylogenetic analyses were done by Bayesian and Maximum likelihood phylograms of ITS, β-TUB and translation elongation factor gene (TEF). The Bayesian inferences of ITS and a combined data matrix (ITS, β-TUB and TEF) produced phylograms with well-resolved topologies with our isolate IISR-GF5 forming a clade with other E. rostratum isolates. The pathogenicity assays with the fungus showed infectivity on rice and maize under in vivo conditions. Based on our morphological and molecular studies, Exserohilum rostratum (Drechs.) Leonard & Suggs was identified as the causal agent of unique leaf blight in ginger and theleaf blight is found to be an emerging threat to ginger cultivation.