Effect of storage and culture media on pathogenicity of Alternaria alternata causing leaf spot disease of date palm

This study investigates the influence of culture media and storage duration on the growth, sporulation, and pathogenicity of Alternaria alternata, a pathogen causing leaf spot disease in date palms. Six culture media were assessed for fungal growth, with Potato Dextrose Agar (PDA) exhibiting the highest radial growth (9 cm) and sporulation (1.2 × 10⁷ spores/mL), followed by Malt Extract Agar (MEA). Moderate growth occurred on Corn Meal Agar (CMA) and Czapek Dox Agar (CDA), while Sucrose Yeast Peptone Agar (SYPA) and Glucose Yeast Peptone Agar (GYPA) were less effective. After six months of storage at 4°C, PDA maintained superior fungal viability (8.5 cm radial growth and 3.1 × 10⁶ spores/mL), with MEA performing comparably. Pathogenicity tests revealed the PDA grown inoculum caused the highest infection (39.3 mm² infected area) on date palm leaves after six months. However, storage beyond six months significantly reduced fungal growth, sporulation, and pathogenicity. These findings highlight the importance of selecting nutrient-rich media and optimizing storage conditions to preserve fungal viability and virulence, particularly in pathogen research and agricultural management.