Use of silicon oxide and sodium silicate for controlling Trichothecium roseum postharvest rot in Chinese cantaloupe (Cucumis melo L.)

Silicon oxide and sodium silicate were investigated as potential agents for the control of postharvest pink rot in Chinese cantaloupe (cultivar Yujingxing) caused by Trichothecium roseum. In vitro tests showed that sodium silicate, when added to potato dextrose agar (PDA), was effective in suppressing the radial growth of the pathogen on the medium while silicon oxide was ineffective. The effectiveness of sodium silicate increased with concentration and the growth of the fungus was completely inhibited at 100 mM. When melons were dipped in the solutions, both silicon oxide and sodium silicate significantly (P < 0.01) reduced the severity of pink rot of the cantaloupe with lesion diameters reduced by up to 5-fold compared with the controls. Scanning electron microscopy-energy dispersive X-ray (SEM-EDX) analysis showed that Si-treated melons had a smoother surface feature and higher Si levels in the epidermis especially at the stomata and along the junction between the exocarp and mesocarp. Enhanced peroxidase (POD) and phenylalanine ammonialyase (PAL) activities were observed in sodium silicate-treated melons but not in those treated with silicon oxide. The results indicate that different mechanisms might be involved in sodium silicate and silicon oxide-initiated reduction of postharvest pink rot in Chinese cantaloupe.