Morphological and molecular characterization of two graminicolous Exserohilum species associated with cultivated rice and early barnyard grass from Sri Lanka

The genus Exserohilum (Order Pleosporales, Class Dothideomycetes) comprises plant pathogenic hyphomycetous fungi, associated with poaceous hosts. Although numerous pathogenic species of Exserohilum are known globally, only E. turcicum and E. rostratum have been reported from Sri Lanka. In the present study, samples showing the symptoms of leaf blight of Oryza sativa (cultivated rice) and sheath blight of Echinochloa oryzoides (early barnyard grass) were collected and causal agents were primarily identified as Exserohilum spp. based on morphological characters. Molecular phylogenetic analyses based on three loci namely, nuclear ribosomal internal transcribed spacer (ITS), partial glyceraldehyde 3-phosphate dehydrogenase (GPDH) and translational elongation factor (TEF-1α) were used to infer evolutionary relationships and accurate identification. These isolates from O. sativa and Echinochloa oryzoides were identified as Exserohilum rostratum and E. oryzicola respectively. Both records are novel plant-fungal associations from Sri Lanka based on available data. This study suggests the need for morphological and molecular reassessments of emerging and poorly known species of fungi associated with cereals, their wild relatives and other economically important hosts in Sri Lanka.