Cultural, morphological and molecular diversity of Ustilaginoidea virens (Cooke) Tak. isolates causing false smut of rice in different agroclimatic regions of Karnataka

Abstract

The ascomycete fungal pathogen Ustilaginoidea virens (Cooke) Takahshi cause false smut in rice and considerable yield loss. In this study, we collected isolates of U. virens from the rice growing ecosystems of Karnataka and characterized for cultural, morphological and molecular characters. The isolates of the fungus on Potato Sucrose Agar media exhibited distinct colonies with colony growth ranging from 21.50 mm (Uv-20) to 70.00 mm (Uv-15). The colony colour appeared as whitish to yellowish with varied growth pattern from flat, raised flat to fluffy and raised fluffy colonies with sectoring in Uv-1, Uv-3, Uv-6 and Uv-9 isolates. The isolates of U. virens also showed variation in the morphology of spores, where the conidia were globose, irregularly round to elliptical and warty on the surface with spore radius ranging from 2.91 to 5.36 μm. The scanning electron microscopy revealed hyaline globose to irregularly rounded ornamented chlamydospores with prominent spines. Besides cultural and morphological characters, molecular identification of false smut isolates was confirmed through ITS sequencing which showed 91 to 99% identity with U. virens in NCBI-BLAST analysis. Dendrogram constructed using ITS sequence data broadly separated the isolates into two major clusters with divergence among clusters. This ITS (internal transcribed spacer) sequencing of isolates should help better understanding of the phylogenetic relationships among these isolates.