Cultural and Morphological Variability of Alternaria solani Isolates Causing Early Blight of Potato in Different Agro-Climatic Zones of Western Uttar Pradesh, India

Abstract

Early blight caused by Alternaria solani (Ellis & Martin) Jones & Grout is one of the most
economically significant foliar diseases of potato (Solanum tuberosum L.) and is widely prevalent in
the potato-growing belts of Uttar Pradesh, India. Understanding the cultural and morphological
variability among isolates of the pathogen is essential for devising precise disease management
strategies. In the present investigation, nine isolates of A. solani (As1-As9) were collected during a
roving survey from three agro-climatic zones of western Uttar Pradesh, namely Muradabad, Hapur,
and Meerut, during Rabi 2024-25 and 2025-26. All isolates were subjected to detailed cultural and
morphological characterisation on Potato Dextrose Agar (PDA) medium at 25 ± 1°C. Considerable
variability was observed among isolates in colony colour, radial growth, conidial length, conidial
width, and the number of transverse and longitudinal septa. Colony colour ranged from greyish white
to black. Radial growth varied from 79.15 mm (As8) to 83.37 mm (As4). Conidial length ranged from
63.60 μm (As9) to 75.00 μm (As2), while conidial width ranged from 23.61 μm (As8) to 35.76 μm
(As6). The number of horizontal septa ranged from 1 to 2, and the number of vertical septa ranged from
4 to 6. The findings demonstrate that A. solani populations in western Uttar Pradesh harbour substantial
intra-specific variability, which has important implications for disease epidemiology, host resistance
evaluation, and the design of integrated management programmes.