Changes in gene expression and postharvest decay inhibition of papaya (Carica papaya L.) treated with chitosan and Ruta graveolens L. essential oil alone and in combination

摘要

Papaya (Carica papaya L.) is a common and economically important fruit crop in many tropical and subtropical countries. However, being a climacteric fruit presents an elevate metabolic activity, a fast maturation, a high susceptibility to fungal diseases, in particular to anthracnose, caused by Colletotrichum spp., and a consequent short shelf life. Chitosan (CS) coating has shown ability to control postharvest decay and is a promising system for essential oil carrier, like Ruta graveolens L. essential oil (REO). In this study, the effectiveness of CS and REO, alone and combined (CS-REO) on postharvest decay of papaya fruits during storage (9 days at 25°C) and the expression of key genes involved on defense mechanisms at 0.5, 6, 24, 48 and 72 h post treatments (hpt) were evaluated. The REO and CS-REO emulsion reduced the decay incidence by 21, and 37%, respectively, and the disease severity by 22, 29, and 44% with CS, REO and, CS-REO, respectively. The real-time quantitative polymerase chain reaction (RT-qPCR) investigation was performed according to 17 key genes of papaya linked to signaling pathways regulating plant defense, pathogenesis-related protein, cell wall-degrading enzymes, oxidative stress, abiotic stress, and phenylpropanoid pathway. While the REO strongly induces overexpression in the early phase at 0.5 hpt, the CS affected the gene expression mainly starting from 6 hpt. The CS-REO treatment delays the genes upregulation from 0.5 to 6 hpt compared to REO treatment and induce the genes upregulation over time compared with other treatments. Our results suggest that CS help to immobilize the bioactive volatile substances of essential oils, releasing them more slowly and regulating the cell stress. This outcome highlights new information on the induction of defense reactions that can be useful for the control of postharvest diseases of fresh fruit.