Mummified Fruit as a Source of Inoculum and Disease Dynamics of Olive Anthracnose Caused by Colletotrichum spp.

Abstract

Anthracnose, caused by Colletotrichum spp., is a destructive disease of olive fruit worldwide. The objective of this study was to investigate the influence of agronomical and weather factors on inoculum production using detached olive fruit and on the development of epidemics in the field. The pathogen produced very large numbers of conidia on rotted (>1.87 × 10(8) conidia/fruit) or mummified (>2.16 × 10(4) conidia/fruit) fruit under optimal conditions. On mummified fruit, conidial production was highest on mummies incubated at 20 to 25°C and 96 h of wetness. Repeated washings of mummies reduced conidial production until it was very low after five washings. When mummies were placed in the tree canopy, conidial production was not reduced after 6 months (May to October); but, when they were held on the soil or buried in the soil, conidial production comparatively decreased up to 10,000 times. Anthracnose epidemics on susceptible 'Hojiblanca' and 'Picudo' during three seasons (2005-08) were influenced by rainfall, temperature, and fruit ripening, and had three main phases: the latent period (May to October); the onset of the epidemic, which coincided with the beginning of fruit ripening (early November); and disease development, which was predicted by the Weibull model (November to March). No epidemics developed on the susceptible cultivars during the driest season (2007-08) or on the resistant 'Picual' olive during any of the three seasons. These results provide the basis for a forecasting system of olive anthracnose which could greatly improve the management of this disease.