Agroclimatic Influence on Morphological Variability of Early Blight of Potato in Western Uttar Pradesh, India

Abstract

Early blight caused by Alternaria solani is one of the most destructive foliar diseases of potato
(Solanum tuberosum L.) and poses a serious threat to production in western Uttar Pradesh, India's
dominant potato-growing region, where district-level variation in disease incidence and pathogen
morphology remains poorly characterised. In the present study, nine isolates of A. solani (As1-As9)
were collected from three agroclimatic districts Muradabad, Hapur, and Meerut during Rabi 2024-25
and 2025-26; field disease incidence was quantified as per cent disease intensity (PDI) using a standard
0-5 rating scale; and all isolates were characterised on Potato Dextrose Agar at 25 ± 1°C for colony
colour, radial growth, conidial length, conidial width, and septal number, with Koch's postulates
fulfilled for each isolate. The results revealed that disease incidence was highest in Meerut (mean PDI:
37.84-38.95%), followed by Muradabad (27.74-28.72%) and Hapur (22.34-23.85%), and that
morphological variability was district-specific, with Meerut isolates producing the shortest and
narrowest conidia (mean length: 66.78 μm; mean width: 24.56 μm), Muradabad isolates the longest
conidia (mean: 72.17 μm), and Hapur isolates the widest conidia (mean: 30.71 μm), demonstrating that
agroclimatic origin shapes both pathogen phenotype and field disease severity and thereby supporting
the use of multi-location representative isolates in resistance screening and integrated disease
management programmes.