Biological control of olive anthracnose

Abstract

Olive anthracnose, a fungal disease caused by species of the genus Colletotrichum, is responsible for severe yield losses and poor oil quality. Typical symptoms appear in autumn or early winter, when the drupes begin to ripen. Under favorable conditions, symptoms on branches and leaves can also occur, leading to chlorosis, severe defoliation, and death of woody organs. Symptomless infection of flowers and blights have also been reported. Latent fruit infections could play an important role as the inoculum source for the autumn-winter epidemics. Application of systemic fungicides has proved effective in field trials, and pre-flowering sprays contribute to reduce latent infection and the inoculum density for autumn infection. However, public concerns about potential risks on the environment and human health promoted the search for alternative and sustainable means. Therefore, the activity of a new sulfur-based product and biocontrol agents (Bacillus subtilis, and endophytic isolates of Aureobasidium pullulans) in reducing the incidence of olive anthracnose was evaluated under field conditions. The sulfur-based product and B. subtilis applied at the pre-flowering stage were as effective as the chemical fungicides in reducing the incidence of latent infections on drupes. Moreover, some endophytic strains of A. pullulans provided high protection levels against Colletotrichum spp. when applied at the pre-flowering and veraison stages. Overall, data indicated that olive anthracnose can be controlled by using biological means and new products could be considered for introduction in the list of the organic product specification.