First Report of Alternaria in the Olive Agroecosystem of NW Spain: Aerobiological Characterization and Relationship with Meteorological Factors

Alternaria spp. is one of the fungal genera affecting olive cultivation, and its temporal dynamics are influenced by climatic variations occurring throughout the crop's vegetative cycle. The aim of this study was to determine the presence of Alternaria spp. in an olive-growing area in northwestern Spain and to examine the relationship between its airborne concentrations and meteorological variables, in order to preliminarily predict its presence in the atmosphere during the olive tree's phenological cycle. To achieve this, a phenological, aeromycological, and meteorological study was conducted from 2021 to 2024. Alternaria spp. conidia were detected in the air throughout all major phenological stages, with peak concentrations occurring mainly during fruit development. The highest percentages of spores were recorded between 11:00 and 22:00, primarily influenced by temperature and sunlight. During the maturity of fruit stages in 2023 and 2024, isolates from the Alternaria section Alternaria were identified as the cause of olive rot. A predictive model was obtained that estimates the atmospheric concentrations of this type of fungus in the study area, based on average temperature values and hours of sunshine. This study constitutes the first report of Alternaria spp. in an olive-growing area of northwestern Spain and provides models that preliminarily predict its presence. These models can inform growers of the pathogen's presence in the air before visible symptoms appear, thereby reducing the likelihood of infection in susceptible plants when environmental conditions favor its development.