Colletotrichum species have the capacity to produce asymptomatic latent (quiescent) infections on various olive tree tissues: during this symptomless biotrophic phase, the pathogen invades the host without killing them and feeds on living cells. Re-infection of the tree by the repeating conidial stage is then responsible for increased anthracnose symptoms during summer, leading to new growths. Normally developed fruit and fruit damaged by abiotic factors, leaves and stems may have asymptomatic infections of Colletotrichum acutatum and C. gloeosporioides in susceptible cultivars ‘Barnea’, ‘Manzanillo’ and ‘Kalamata’. Anthracnose under favourable conditions can also infect less susceptible cultivars. The infection can persist from season to season, depending on olive cultivar,
environment, crop management, and pathogen virulence. Brown lesions with anthracnose fungal spores were observed in young green stems and leaves and dieback of young shoot tips of olive susceptible cultivars in orchards in early spring and summer. Flowering, fruit set and immature fruits can be observed during fruit development on a single peduncle; both flowers and fruit set late in the season, in summer rather than spring, and carry fungal infection. Immature rotten fruits are mummified. Colletotrichum fungi overwinter in mummified fruits on the tree, woody tissue and leaves; the fungus has long saprophytic survival ability on dead peduncle and pedicels. Fungal inoculum present year-round throughout the canopy. Hemibiotrophic anthracnose fungal pathogens grow first on living tissue and then cause host death in later, necrotrophic growth. The ability to survive and multiply in the absence of symptoms may explain why anthracnose fungi often cause unexpected crop losses in olives. Successful management of anthracnose relies on understanding the conditions that promote disease development. The complexities of anthracnose epidemiology, including the presence of different species, point to the need for continued research around disease management, particularly regarding new control strategies for Colletotrichum in olives.
The Role of Epidemiology Data in Developing Integrated Management of Anthracnose in Olives – a Review