In vitro Evaluation of Fungicides against Alternaria alternata Causing Leaf Blight of Tuberose

Background: Tuberose (Polianthes tuberosa L.) is a commercially important ornamental crop widely cultivated for its highly fragrant flowers and significant economic value in the floriculture industry. However, its production is severely constrained by several diseases, among which leaf blight caused by Alternaria alternata has emerged as a major threat. The disease is particularly destructive under favourable environmental conditions, leading to significant reductions in flower yield and quality, thereby affecting marketability and profitability. Aims: The present investigation was undertaken to evaluate the efficacy of selected systemic, contact, and combination fungicides against Alternaria alternata under in vitro conditions. Despite the economic importance of tuberose, comprehensive information on the comparative efficacy of different classes of fungicides against A. alternata is limited. Place and Duration of Study: The study was carried out under controlled laboratory conditions using standard in vitro techniques at Department of Plant Pathology, University of Agricultural Sciences Bangalore from April to June 2025. Methodology: Twenty-one fungicides, including seven systemic, seven contacts, and seven formulations, were evaluated using the poisoned food technique on potato dextrose agar medium. Systemic fungicides were tested at 500, 750, and 1000 ppm, whereas contact and combination fungicides were tested at 1000, 1500, and 2000 ppm concentrations. The experiment was laid out in a completely randomized design with three replications, and per cent inhibition of mycelial growth was calculated. Results: Significant variation in fungicidal efficacy was observed among treatments. Among systemic fungicides, Propiconazole completely inhibited mycelial growth (100%), followed by Hexaconazole (98.33%) and Difenoconazole (94.35%). In contact fungicides, Metiram recorded the highest inhibition (76.32%), followed by Mancozeb (73.59%) and Propineb (70.02%). Among combination fungicides, Captan + hexaconazole, Boscalid + pyraclostrobin, and Metiram + Pyraclostrobin achieved complete inhibition (100%), demonstrating superior efficacy over individual fungicides. Conclusion: The findings highlight the superior performance of triazole-based systemic fungicides and selected combination formulations in suppressing Alternaria alternata. These fungicides offer potential for incorporation into integrated disease management strategies for effective control of tuberose leaf blight.