Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2005
Publication Date: 6/1/2005
Citation: Smilanick, J.L., Mansour, M., Margosan, D.A., Gabler, M., Goodwine, W.R. 2005. Influence of ph and nahco3 on the effectiveness of imazalil to inhibit germination of spores of penicillium digitatum and to control postharvest green mold on citrus fruit. Plant Disease. 89:640-648.
Interpretive Summary: Harvested citrus fruit often rot before they can be consumed because of fungal molds. We showed how one crop protectant chemical, the fungicide imazalil, could be made to work more effectively reduce rot losses if the imazalil solution was more alkaline when it was applied to the fruit. Improved imazalil performance by the methods we described reduce the amount of the chemical that remains in the fruit reaching consumers, and reduces the amount of imazalil growers must buy, which can be a significant expense.
Technical Abstract: In vitro, spores of Penicillium digitatum germinated without inhibition between pH 4 and 7, but were inhibited at higher pH. Estimated ED50 imazalil (IMZ) concentrations to spores 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 lemons 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 lemons 24 hr after immersion in 1, 2, or 3% NaHCO3 increased from pH 5.3 to 6.0, 6.3, and 6.7, respectively. Green mold incidence among lemons inoculated with M6R and treated 24 h later with 10 µg/ml IMZ, 1% NaHCO3, or their combination, was 92, 55, and 22%, respectively. Green mold among lemons inoculated with D201, and treated 24 h later with 500 µg/ml IMZ, or with 1, 2, or 3% NaHCO3, was 95, 93, 75, and 37%, respectively; when combined with 1, 2, or 3% NaHCO3, green mold incidence reduced to 55, 20, and 9%, respectively. NaHCO3 did not influence IMZ fruit residue levels.