Sodium bicarbonate induces crystalline wax generation, activates host-resistance, and increases imazalil level in rind wounds of oranges, improving the control of green mold during storage

The influence of the immersion of lemon fruit in aqueous imazalil (IMZ) mixtures at 25 or 50 °C on the deposition and persistence of IMZ within the fruit rind and its effectiveness in controlling postharvest green mold, caused by Penicillium digitatum, was investigated. Concentrations of IMZ in the albedo tissue surrounding deep wounds in the rind were higher than the mean EC50 values for IMZ-resistant strains (1.0 ?g ·mL-1) after immersion of fruit into IMZ mixtures containing 25, 50, or 75 mg· L-1 heated to 50 °C, but not those at 25 °C, where fungicide deposition was insufficient. IMZ residue, one day after treatment with 25, 50, or 75 mg· L-1, was 3, 5, or 7 times higher after treatment at 50 °C compared to treatment at 25 °C. IMZ residues within the albedo of unwounded fruit treated with 25, 50, or 75 mg· L-1 at 50 °C were 0.8, 1.3, or 2.0 ?g · g-1, respectively, while those similarly treated at 25 °C had negligible residues. Residues following treatment at 50 °C in the albedo did not decline during storage at 10 °C after 60 days. IMZ residues in the flavedo were higher than those in the albedo: after treatment with 25, 50, or 75 mg· L-1 IMZ, they averaged 1.0, 1.2, or 2.7 ?g · g-1, respectively, after treatment at 25 °C, and 5.5, 7.9, or 16.2 ?g · g-1, respectively, after treatment at 50 °C. IMZ effectiveness as an eradicant to control green mold improved when it was heated. Green mold was reduced by 22 or 95% after treatment of lemons inoculated 1 h before immersion of lemons in IMZ at 50 mg· L-1 at 25 or 50 °C, respectively. Green mold was reduced by 18 or 61% after treatment of lemons inoculated 1 day after immersion of lemons in IMZ at 50 mg· L-1 at 25 or 50 °C, respectively. Scanning electron microscopy of the rind surface indicated that treatment at 50 °C for 2 min also caused ruptures in the cuticle.