Abstract

Alternaria diseases, caused by Alternaria solani (Early Blight) and A. alternata (Brown Spot), threaten potato production globally. This study quantified the epidemiological patterns of the diseases, climate-disease interactions, transmission dynamics, and economic impacts across three climatically different zones of Eritrea (Adi Keih, Asmara, and Halhale) during the 2025 growing season. A randomized complete block design with four treatments of different pathogen inoculation times, with three replications, was used. Disease assessments were conducted at five crop development stages. Apparent infection rate, area under disease progress curve (AUDPC), ANOVA, Pearson correlation, and linear regression were used for statistical analysis. Asmara exhibited high disease risk with Early Blight severity of 4.19 and Brown Spot severity of 3.13, with 100% incidence and the highest transmission rates (0.122/day for Early Blight, 0.108/day for Brown Spot). Moderate humidity (54.1%) combined with warmer temperature (19.2 °C) was found to be conducive. Across all places, the disease progressed rapidly between 30 and 45 days after planting. Negative correlations between transmission efficiency and yield were observed for both diseases. Yield losses reached 42% (13 t/ha) in high transmission environments, which is approximately Eritrean Nakfa (ERN) 130,000/ha (USD 8,667/ha) in economic losses. Inoculation timing did not affect AUDPC values, indicating that environmental factors outweigh pathogen incidence timing. Our findings indicate that moderate humidity (54-58%) coupled with warmer temperatures (19-20 °C) create ideal conditions for disease transmission, adding a scientific basis for understanding Alternaria epidemiology. The critical crop age period of 30-45 days after planting represents the highest vulnerability window requiring intensive monitoring. These findings, while based on a single growing season, provide a foundation for multi-year validation across broader geographic scales. Our study supports the development of site-specific, climate-informed, and economically optimized integrated disease management strategies that can help farmers achieve sustainable potato production in the face of changing climate conditions.

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