Ozone and electrolized water application to preserve quality of citrus fruit and effect of ozone on gene expression related to plant defense mechanisms

In this work the effect of ozone (O3), electrolyzed water (EW) in combination with passive refrigeration conservation system (PRS) on fruit quality was studied during postharvest. The amount of Colony Forming Units (CFUs) on fruit surface, shelf life (McKinney index), firmness and sugar content were evaluated during the conservation period of Citrus (cv. Navel orange and cv. Clementine commune), cherry (cv. Ferrovia) and table grape (cv. Redglobe, Crimson and Italia). O3 and EW dose and exposure time were set in in vitro experiment. O3 was used in washing water or as gas during storage. Results demonstrate that the combination of O3, EW and PRS treatments reduce microorganism contamination and increase fruits hardness and sugar content. An extension of fruit shelf-life was also evidenced. Elicitors are agents that can induce a range of defense mechanisms in citrus tissue. This characteristic results in a broad spectrum of metabolic modifications such as Systemic Acquired Resistance (SAR), Induced Systemic Resistance (ISR) and production of Reactive Oxygen Species (ROS). In the present study we investigated the expression level of genes that encode Beta-1,3 glucanase (GNS1), Chitinase (CHI1), Phenylalanine-Ammonia Lyase (PAL1) and Peroxidase (POD1) in Navel sweet orange treated with two elicitors: ozone and Penicillium digitatum. Quantitative Reverse Transcriptase PCR (qRTPCR) showed that ozone applied singly increased the transcription of (GNS1) and (CHI1) with a fold change of 22 and 21 above the levels observed for the control at 24 hours and 48 hours after treatment. Unexpectedly, P.digitatum inoculation followed by ozone treatment was weakly effective in enhancing the tested genes. Overall, we consider that ozone can enhance the genes related to SAR (CHI1 and GNS1) in non-inoculated fruits. Therefore, ozone can be used as post-harvest treatment immediately after picking, before the exposure of fruits to pathogens. This lead to suggest fruit washing with EW storing in PRS under ozonized atmosphere, to counteract a pathogenic attack or in general a stress event.