Cellulolytic and pectinolytic activities of Capnodium isolates (sooty mould) from Zimbabwe

Abstract

The cellulolytic and pectinolytic activities of five Capnodium (sooty mould) isolates previously associated with preharvest spoilage of avocado (Persea americana Mill.) fruits in Zimbabwe were assessed in liquid culture and in artificially infected avocado fruits. Polygalacturonase, endo-1,4-β-glucanase, and exo-1,4-β-glucanase activities were determined by measuring the increase in reducing groups using the dinitrosalicylic acid method, while for pectin lyase activity the thiobarbituric acid method was used. The five isolates showed the ability to produce polygalacturonase, pectin lyase, and endo-1,4-β-glucanase enzymes. Exo-1,4-β-glucanase activity was only detected in infected avocado tissue. The greyish black Capnodium isolates (Av7, Av8, and Av12) belonging to group I showed higher polygalacturonase and pectin lyase activities in both liquid culture and infected fruits than isolates Av3 and Av10 from group II. The same isolates showed higher exo-1,4-β-glucanase activity in infected avocado fruits. Results indicate that Capnodium, which normally is nonpathogenic, secretes cell wall degrading enzymes, especially pectic and cellulase enzymes. The detection of these enzymes in inoculated avocado fruits suggests a possible role in the preharvest soft rot of avocado fruits caused by Capnodium in Zimbabwe.Key words: Capnodium, sooty mould, pectic enzymes, avocados, cellulases.