Characterization of Fungi Associated with Olive Fruit Rot and Olive Oil Degradation in Crete, Southern Greece.

In November 2019, a severe outbreak of fruit rot was observed in olive orchards in Crete, southern Greece. Symptoms appeared primarily on fruits and stalks, resembling those caused by anthracnose. Typical symptoms were fruit rot, shrinkage, and mummification, associated commonly with stalk discoloration and fruit drop. Disease incidence was estimated at up to 100% in some cases, and an unprecedented increase in olive oil acidity reaching up to 8% (percentage of oleic acid) in severely affected olive groves was recorded. Thirty-two olive groves were then surveyed, and samples of fruit, stalk, leaf, and shoot were collected. Visual, stereoscopic, and microscopic observations revealed several fungi belonging to the genera , , , , and . Fungal infection in fruits was commonly associated with concomitant infestation by the olive fruit fly along with increased air temperature and relative humidity conditions that prevailed in October and November 2019. Twenty representative fungal strains isolated from symptomatic fruits and stalks were characterized by morphological, physiological, and molecular analyses. By internal transcribed spacer regions of ribosomal DNA region and translation elongation factor 1-α gene sequencing analysis, these isolates were identified as spp., , , , , species complex and . Pathogenicity tests on punctured fruits revealed that all isolates were pathogenic; however, isolates along with were the most virulent, and wounds were necessary for efficient fungal infection. Moreover, as few as 10 spores of were sufficient to cause significant infection in punctured fruits. was also capable of infecting olive fruits in the presence of , with no additional wounding, in artificial inoculation experiments. Moreover, it was capable of colonizing and affecting olive blossoms. Further analyses of olive oil extracted from fruits artificially inoculated with indicated a significant increase in oil acidity, K, K, and peroxide value, whereas total phenol content was significantly decreased. To the best of our knowledge, this is the first report of associated with olive fruit rot and olive oil degradation worldwide.