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Influence of pH and NaHCO₃ on Effectiveness of Imazalil to Inhibit Germination of Penicillium digitatum and to Control Postharvest Green Mold on Citrus Fruit

In vitro, spores of Penicillium digitatum germinated without inhibition between pH 4 and 7, but were inhibited at higher pH. Estimated concentrations of imazalil (IMZ) in potato-dextrose broth-Tris that caused 50% reduction in the germination of spores (ED₅₀) of an IMZ-sensitive isolate M6R at pH 4, 5, 6, and 7 were 0.16, 0.11, 0.015, and 0.006 μg/ml, respectively. ED₅₀ IMZ concentrations of an IMZ-resistant isolate D201 at pH 4, 5, 6, and 7 were 5.9, 1.4, 0.26, and 0.07 μg/ml, respectively. The natural pH within 2-mm-deep wounds on lemon was 5.6 to 5.1 and decreased with fruit age. IMZ effectiveness to control green mold and its residues increased with pH. The pH in wounds on lemon fruit 24 h after immersion in 1, 2, or 3% NaHCO₃ increased from pH 5.3 to 6.0, 6.3, and 6.7, respectively. NaHCO₃ dramatically improved IMZ performance. Green mold incidence among lemon fruit inoculated with M6R and treated 24 h later with IMZ at 10 μg/ml, 1% NaHCO3, or their combination was 92, 55, and 22%, respectively. Green mold among lemon fruit inoculated with D201 and treated 24 h later with water, IMZ at 500 μg/ml, 3% NaHCO₃, or their combination was 96.3, 63.0, 44.4, and 6.5%, respectively. NaHCO₃ did not influence IMZ fruit residue levels.