Portuguese propolis from Caramulo as a biocontrol agent of the apple blue mold

Abstract

Diseases arising during fruit conservation are one of the main constraints to their marketing and consumption, with negative economic repercussions besides increasing food waste. Apple is globally one of the most important, among fruit crops, and its main post-harvest diseases are fungal rots, like blue mold caused by the fungus Penicillium expansum Link, accounting for up to 20% of apple production losses worldwide. Post-harvest disease control is currently managed by using synthetic fungicides that are harmful to the environment and to the consumer, thus demanding for equally effective but safer and more ecofriendly alternatives. Propolis, a natural product of the hive known for its various bioactivities, namely antimicrobial, becomes therefore an excellent candidate for applications other than medicine, where it has been widely used for centuries. In Portugal, as in other countries, propolis production targets mainly pharmaceutical and nutraceutical applications, with more stringent requirements than others, and samples that do not comply with such requirements are rejected and end up as leftovers. In the present work, the antifungal potential of the hydroalcoholic extract of a Portuguese propolis sample considered unsuitable for pharmaceutical purposes was studied in vitro and in vivo against P. expansum. In vitro, a reduction of 48% in mycelium growth was observed four days after inoculation in medium with the extract (2000 mu g/mL). In vivo, 5% (w/v) of the same extract reduced by 66.5% the lesion size caused by this fungus in Golden Delicious apples, 14 days after subepidermal inoculation. The application of the extract by the same procedure caused no relevant phytotoxic effects in fruit tissues, supporting the potential of this natural product as a biocontrol agent against P. expansum in apples.