Epidemiology of Late Blight (Phytophthora infestans) of Potato in District Mansehra, Khyber Pakhtunkhwa, Pakistan

Abstract

Late blight, caused by the oomycete Phytophthora infestans (Mont.) de Bary, is among the most damaging diseases of potato worldwide and a recurrent constraint in the hilly potato-growing tracts of northern Pakistan. Under favourable conditions the pathogen sporulates profusely and can destroy foliage within days. During the winter (Rabi) cropping season of 2017–2018, a systematic survey of four tehsils of District Mansehra including Baffa, Mansehra, Balakot, and Oghi & Darband was conducted to determine the prevalence, incidence, and severity of late blight of potato, and the pathogen was isolated and confirmed by culturing on corn meal agar followed by amplification and sequencing of the internal transcribed spacer (ITS) region. Late blight was recorded in every tehsil surveyed but not in every field. Disease pressure was highest at Balakot, where prevalence reached 100 %, disease incidence ranged 25–35 %, and severity ranged 25–55 %; the disease was comparatively milder at Baffa, Mansehra, and Oghi & Darband. The relatively moderate epidemic of 2017–2018 was attributed to below-normal rainfall and consequently lower relative humidity during the crop season, conditions unfavourable for infection by P. infestans. These field observations are consistent with recent epidemiological work showing that late blight incidence and severity are positively correlated with temperature and with morning and evening relative humidity, and that prolonged leaf wetness and elevated dew-point drive epidemic build-up. The study confirms that late blight remains an established, weather-driven threat to potato in Mansehra and that anticipatory, forecast-guided management is warranted.