Vishwa Vijay Raghuvanshi, Pradip Kumar, Pramod Kumar Singh, S.K. Singh, Manoj Kumar Singh, Subhash Chandra, Shivam Singh, Anand Milan, Archana Kushwaha, Jitendra Kumar and Sanjay Kumar Yadav
Abstract
Early blight caused by Alternaria solani, is the most common, widely distributed disease affecting potato crops. This study aimed to isolate, identify, and confirm the pathogenicity of A. solani responsible for early blight in potato. Symptoms typically appeared 25-30 days after sowing and initially manifested as small, dark brown lesions (0.3-0.4 cm) on older leaves. These lesions often exhibited characteristic concentric rings forming a target-like pattern. The pathogen was isolated from symptomatic potato leaves on potato dextrose agar (PDA) medium. Pure cultures were obtained using the hyphal tip culture technique after eight days and preserved at 5 °C for further study. Microscopic examination showed septate, branched mycelium that turned from light brown to dark brown or olive with age. The conidia were muriform, measuring 140-230 µm in length and 12.4-17.2 µm in width, with 4-10 transverse and 1-4 longitudinal septa and a distinct beak. Pathogenicity tests were conducted under the controlled conditions on healthy potato plants and via a detached leaf technique. In bothmethods, characteristic early blight symptoms developed within 3-5 days post-inoculation. Inoculated leaves showed brown to black lesions with concentric rings, while control plants and leaves remained symptomless. The pathogen was successfully re-isolated from infected tissues, confirming its identity and pathogenicity in accordance with Kochâs postulates.