Epidemiology, Occurrence and Severity of Early Blight of Potato Caused by Alternaria solani (Sorauer)

Abstract

Early blight of potato caused by Alternaria solani (Sorauer) remains a significant foliar problem in Uttar Pradesh; however, much of the research on its weather-driven epidemiology in the state is based on earlier studies and often considers more than one site at a time. A field survey was conducted during the 2022 Rabi season at five locations across the state—Kanpur, Kannauj, Agra, Meerut and Varanasi—which were selected to capture meaningful variation in winter temperature, humidity and soil conditions. Six commercial fields were monitored at each site. All fields were planted within a narrow window between 15 and 25 October 2022 and received no fungicide application, thereby allowing natural disease progression to be recorded. Disease severity was assessed weekly using the 0–5 scale of Horsfall and Barratt (1945) and expressed as the percent disease index (PDI). The pathogen was isolated from ten symptomatic leaves per location, purified, characterised morphologically and confirmed as pathogenic on Kufri Bahar through glasshouse inoculation. Local weather records were obtained from the observatory nearest to each field, and PDI was related to nine weather variables using Pearson correlation and full-model multiple linear regression. Disease appeared earliest at Agra (9 November 2022) and latest at Kanpur (22 November 2022). Final PDI ranged from 27.68 % at Kanpur to 38.46 % at Agra; the apparent infection rate ranged from 0.0859 units day−1 at Varanasi to 0.1266 units day−1 at Kanpur, and AUDPC ranged from 548.6 %-days at Kanpur to 1024.8 %-days at Agra. Maximum and minimum air temperatures showed consistent negative associations with PDI at every site.