Early Blight of Potato Caused by Alternaria solani (Sorauer): A Critical Review of Epidemiology, Weather Relations, Disease Assessment and Management

Abstract

Early blight, caused principally by the necrotrophic fungus Alternaria solani, remains one of the most persistent foliar constraints on potato (Solanum tuberosum L.) production across temperate and subtropical growing regions. The disease progresses through repeated infection cycles governed closely by temperature, leaf wetness duration and relative humidity, and it interacts with crop phenology in ways that complicate both its prediction and its control. This review synthesises recent literature on the taxonomy and biology of the causal organism, the weather variables that regulate sporulation and infection, the tools available for disease assessment ranging from visual scoring to molecular diagnostics and deep learning-based image analysis, the forecasting and decision support systems developed to time fungicide applications, and the chemical, genetic, biological and cultural strategies used to manage the disease. Particular attention is given to the species complex now recognised within large-spored Alternaria, to the divergence of fungicide sensitivity associated with quinone outside inhibitor and succinate dehydrogenase inhibitor chemistries, and to the quantitative and largely polygenic nature of host resistance. Evidence from multi-year field trials indicates that realised yield losses vary considerably with soil type, cultivar maturity and season, complicating generalisations about economic impact. The review concludes that sustainable management depends on the integration of resistant or partially resistant cultivars, weather-informed spray timing, judicious fungicide rotation and improved diagnostic sensitivity, rather than reliance on any single tactic. Gaps remain in the genetic basis of durable resistance, in the transferability of forecasting models across climatic zones, and in the practical deployment of digital diagnostic tools at farm scale.