First report of Colletotrichum acutatum causing anthracnose on olives in Greece.
Anthracnose is the main disease of olive (Olea europaea) fruit that is caused by different species of Colletotrichum spp. primarily belonging to two complexes, C. acutatum sensu lato (s.l.) and C. gloeosporioides s.l. Observations in January 2015 in >20 olive groves in the Aitoloakarnania region (West-Central Greece) showed severe symptoms of mummified fruits in ∼50% of olive cv. Kalamon trees. In March 2015, severe brown discoloration of inflorescences with 40-50% disease severity was observed in >15 orchards of cultivar Koroneiki in the island of Zakynthos (West Greece). In autumn 2015, mature olive fruits showed typical anthracnose symptoms with dark necrotic lesions and rot with abundant orange conidial masses that resulted in premature fruit drop or mummification. Symptoms appeared also on tree twigs and leaves, leading to necroses, severe defoliation, and branchlet death. The disease also affected the oil quality by increasing the acidity and the peroxide number in oil-producing varieties. Since then, autumn and winter heavy rainfalls resulted in extensive spread of anthracnose in West Greece and Peloponnese in 2016, causing severe losses in several olive cultivars. Based on morphological characteristics, multi-gene sequence analysis and pathogenicity tests, the causal agent was identified as C. acutatum. This is thought to be the first report of C. acutatum causing fruit rot and flower and leaf necroses on olive trees in Greece.