Effect of extracts of wastewater from olive milling in postharvest treatments of pomegranate fruit decay caused by Penicillium adametzioides

Nonclimateric pomegranate (Punica granatum L.) fruit harvested at full ripening are susceptible to attack by different genera of pathogenic fungi such as Alternaria, Aspergillus, Botrytis, Colletotrichum, Coniella, Nematospora, Penicillium, Pestalotiopsis, Pilidiella, Rhizopus and Syncephalastrum which can cause rot of the fruits thus compromising their organoleptic and nutritional value. Seven fungal species belonging to the genus Penicillium such as Penicillium expansum, Penicillium herquei, Penicillium implicatum, Penicillium glabrum, Penicillium minioluteum, Penicillium purpurogenum and Penicillium sclerotiorum have been previously identified as causal agents of postharvest pomegranate decay. Based on culture characteristics, molecular analyses on internal transcribed spacers, beta-tubulin gene sequences, and pathogenicity tests, Penicillium adametzioides S. Abe ex G. Sm. is identified as a causal agent of pomegranate fruit rot. To the best of our knowledge, this is the first report of P. adametzioides as a pathogen of P. granatum. A phenolic concentrate obtained from olive-mill wastewater through a membrane filtration process, and its related purified phenolic extract that has a lower reducing sugar content, were produced and tested in vitro and in vivo against P. adametzioides. Both the phenolic concentrate and the purified phenolic extract significantly reduced mycelial growth and conidial germination of P. adametzioides when applied at 4 mg mL-1 and 8 mg mL-1 phenols. At the same content of phenols, the greater reduction of mycelial growth by the purified phenolic extract was related to its lower sugar content. Of note, the purified phenolic extract at 4 and 8 mg mL-1 phenols protected pomegranate fruit in vivo against P. adametzioides. Postharvest application of such by-products of the olive-oil industry might represent an alternative use of olive-mill wastewater, where its high content of phenols results in a disposal problem. This olive-mill wastewater also represents an alternative means for safe disease control of pomegranate fruit.