Characterisation and In-vitro Fungicide Susceptibility of Corynespora cassiicola Associated with Leaf Spot Disease of Aglaonema Ruby Garuda

Abstract

During 2020- 2022, a characteristic leaf spot symptom was recorded from the Aglaonema cultivar, Aglaonema Ruby Garuda Aglaonema Ruby Garuda from Ambunadu region, Ernakulam district of Kerala. The symptomatic plants formed dark brown, water-soaked, circular spots with concentric zonations and recorded 30 per cent disease severity. Pathogen associated with the symptom isolated using standard isolation methods and pathogenicity of the fungal isolates was established. Greyish brown mycelial growth was observed in culture plates with greyish black colour on the reverse side. Conidia of the fungus were sub hyaline to pale brown, solitary, straight to slightly curved, obclavate produced on brown septate mycelia with a dimension of 27.3-47.8 µm × 4.2-12.8 µm. The amplicon sequences of internal transcribed spacer (ITS) and translational elongation factor 1- alpha (TEF1-α) regions of the pathogen were analysed with the nucleotide sequences in nBLAST database and identified as Coryenespora cassiicola. Evolutionary relationship of the pathogen with related organisms were identified by constructing phylogenetic tree using ITS and TEF1-α sequences. In vitro efficacy of 11 chemical fungicides at different dosages and three biocontrol agents tested recorded, cent per cent inhibition with contact fungicides viz. mancozeb, propineb, Bordeaux mixture. Complete inhibition was observed with systemic fungicides, hexaconazole 5EC, tebuconazole 25.9EC, carbendazim 50WP at all test dosages. Among the combination fungicides, carbendazim 12%+ mancozeb 63% was superior with cent per cent mycelial inhibition. Among the biocontrol agents, the fungal antagonist, Trichoderma asperellum (KAU reference culture) recorded complete inhibition against Coryenespora cassiicola by dual culture assay.