Impact of Temperature and Humidity Variability on the Development and Epidemiology of Major Tomato Diseases under Changing Climatic Conditions
Naiba Valiyeva1* 
, Gunel Ramazanova1 ,
Sahila Mammadova1 , and Gulnara Abbasova1
Abstract. Climate variability influences crop disease epidemiology by modifying host susceptibility, pathogen development, and infection conditions. Tomato (Solanum lycopersicum L.), an economically important vegetable crop, is particularly sensitive to temperature and relative humidity fluctuations. This study evaluated the relationship between temperature and relative humidity variability and major tomato diseases under greenhouse conditions at Azerbaijan State Agricultural University (ADAU), Ganja, Azerbaijan, during the 2024 and 2025 growing seasons. Particular attention was given to late blight caused by Phytophthora infestans, powdery mildew associated with Leveillula taurica and/or Oidium neolycopersici, and gray mold caused by Botrytis cinerea. Greenhouse air temperature and relative humidity were monitored, and symptomatic plant tissues were assessed visually and microscopically. The results revealed distinct temporal and microclimatic patterns of disease occurrence. Late blight and gray mold were observed more frequently under moderate temperatures and relatively high humidity, whereas powdery mildew remained detectable under warmer and moderately humid conditions. Joint assessment of temperature and relative humidity showed that late blight and gray mold occurred primarily under moderate-temperature/high-humidity combinations, while powdery mildew was associated with moderately warm/intermediate-humidity conditions. Microscopic examination revealed morphological structures consistent with the respective disease groups, supporting symptom-based diagnosis. Late blight and gray mold occurred most frequently at 18–24 °C and 82–89% RH, whereas powdery mildew was predominantly observed at 22–28 °C and 60–78% RH. These findings indicate that temperature and relative humidity jointly influence major tomato disease occurrence patterns under greenhouse conditions. Integrating microclimatic monitoring with regular visual and microscopic disease assessment may improve disease surveillance and support climate-adaptive disease management in tomato production.
Keywords: Solanum lycopersicum, climate variability, greenhouse microclimate, plant disease epidemiology, temperature, relative humidity, Phytophthora infestans, Botrytis cinerea, powdery mildew