The involvement of fungi in the breakdown of sulphited strawberries

The presence of strawberries infected with Mucor piriformis, Rhizopus sexualis, or R. stolonifer in a sample of sulphited whole berries caused complete breakdown of the whole sample of fruit. As little as 1‐2% of infected tissue for each of the three species consistently caused breakdown while with R. sexualis even 0.1 % resulted in some softening and breakdown of the fruit. Similar results were obtained when culture filtrates possessing pectolytic activity, of each of the above fungi, were added to sulphited fruit. In addition culture filtrates of other pectolytic fungi associated with strawberries, Aureobasidium pullulans, Trichosporon pullulans and Cryptococcus albidus var. albidus were also shown to cause breakdown. It is suggested that the disintegration of the fruit is due to fungal pectolytic enzymes, most probably polygalacturonases. The addition of berries infected with Botrytis cinerea or culture filtrates of this fungus, possessing pectolytic activity, to sulphited healthy fruit did not cause any softening or breakdown.