Effects of postharvest sodium silicate treatment on pink rot disease and oxidative stress-antioxidative system in muskmelon fruit

Sodium silicate (Si) at 100 mM was used as a postharvest treatment agent of induction resistance on muskmelon (Cucumis melon L. cv. Yindi) to investigate the mechanism of controlling pink rot disease, which caused by Trichothecium roseum. Si treatment significantly reduced (P < 0.05) the lesion diameter of melons inoculated with T. roseum during storage. Si treatment increased the content of superoxide (O₂^•−) and could be further raised by challenged with T. roseum inoculation. The content of hydroxyl radical (·OH) in inoculated fruit was also increased. Both malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) were also accumulated with Si treatment and challenged inoculation. Si treatment maintained membrane integrity in non-inoculated fruit, as compared to untreated control. Si treatment and challenge inoculation significantly (P < 0.05) increased the activity of superoxide dismutase (SOD), glutathione reductase (GR), peroxidase (POD), and polyphenoloxidase (PPO), while markedly decreased the activity of catalase (CAT) and ascorbic peroxidase (APX). Si treatment and challenge inoculation also enhanced the content of ascorbic acid (ASA) and glutathione (GSH). These findings suggested that the effects of sodium silicate on postharvest disease in muskmelon fruit may be associated with the elicitation of antioxidant defense system in fruit.