First Report of Fusarium acutatum as the Causal Agent of Pokkah Boeng Disease of Sorghum in Northern Karnataka, India

Abstract

Background: A broad range of diseases affect sorghum which is the major constraint to its production. The most destructive sorghum diseases reported are incited by fungal pathogens, which are widespread globally and result in huge losses in yields both in terms of the quantity and quality of the grains. Aim: The present study identifies the causal agent of Pokkah boeng disease of sorghum in northern Karnataka using a combination of morphological and molecular techniques. Place and Duration of Study: The study was conducted during kharif 2024 in the fields of Main Agricultural Research Station and the Department of Plant Pathology of UAS, Dharwad, Karnataka, India. Methodology: Infected sorghum leaf samples were collected and the pathogen was isolated on potato dextrose agar (PDA). Genomic DNA was isolated for molecular analysis. Morphological observations were taken both macroscopically and microscopically. PCR amplification was done using ITS and TEF primers, and sequenced. A phylogenetic tree was constructed in MEGA software using the sequences obtained for ITS as well as TEF. SDT analysis was also done to understand the identities between the isolates and reference species used. Results: Pathogenicity test confirmed the isolate’s ability to induce disease symptoms in healthy sorghum seedlings, fulfilling Koch’s postulates. The isolate showed white, fluffy growth and had long, curved spores with three septations, as well as oval spores without septations, which are typical features of Fusarium. Molecularly, DNA was extracted, and the internal transcribed spacer (ITS) and translation elongation factor 1-alpha (TEF) regions were sequenced. The obtained sequences of ITS and TEF genes showed 99.75 and 99.81 per cent identity, respectively, to the Fusarium acutatum in the FUSARIOID-ID database, thus confirming the identity. The phylogenetic analysis using the Maximum Likelihood method clustered the isolate with F. acutatum strains, supported by high bootstrap values. Pairwise identity of nucleotide and amino acid sequences of ITS and TEF genes, calculated between the isolate and the reference species. Conclusion: This study marks the first report of F. acutatum as the causal agent of Pokkah boeng disease in sorghum in northern Karnataka, differing from prior reports indicating other Fusarium species.