Pre-harvest spoilage of avocado (Persea americana) fruits by Capnodium isolates in Zimbabwe

Abstract

Thirteen fungal isolates associated with pre-harvest spoilage of avocado fruits were isolated on potato dextrose agar by incubating the infected avocado fruit tissue segments at 25 oC for 7 days. Three types of fungi were isolated from the infected tissue namely Glomerella cingulata (Stonem.), Aureobasidum pullulans (De Bary) and Capnodium sp. (Mont.). Capnodium sp. had the highest frequency (90.9 %) while only a single isolate was isolated for Aureobasidium pullulans. Pathogenicity tests using avocado fruits showed that Capnodium and Glomerella cingulata isolates caused soft rot symptoms similar to those observed on infected avocado fruits on the tree. Capnodium isolates gave the highest lesion diameter (3.0-7.1 cm) while Aureobasidium pullulans did not cause any lesion or soft rot symptoms on inoculated avocados. Although avocados are known to be hosts to Capnodium sp., in Zimbabwe, this is the first report implicating Capnodium sp. in the pre-harvest spoilage of avocado fruits. Preliminary studies show that Capnodium isolates produce cell wall degrading enzymes especially pectic and cellulolytic enzymes which are known to play a major role in most soft rot diseases.

Keywords: Capnodium, sooty mould, pre-harvest spoilage, pathogenicity