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Use of Phosphite Salts in Laboratory and Semicommercial Tests to Control Citrus Postharvest Decay

February 2013 , Volume 97 , Number  2
Pages  201 - 212

L. Cerioni and V. A. Rapisarda, Instituto Superior de Investigaciones Biológicas–INSIBIO (CONICET-UNT), Chacabuco 461, Tucumán, CP T4000ILI, Argentina; J. Doctor, FGS Packing Services, Exeter, CA 93221; S. Fikkert, Plant Protectants, Inc., Visalia, CA 93291; T. Ruiz and R. Fassel, Pace International Co., Seattle 98101; and J. L. Smilanick, United States Department of Agriculture–Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, Parlier, CA 93648

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Accepted for publication 23 August 2012.

Potassium phosphite (KP) concentrations that inhibited the germination of 50% of Penicillium digitatum conidia were 229, 334, 360, 469, 498, or 580 mg/liter at pH 3, 4, 5, 6, 7, or 8, respectively. Increasing phosphate content in media reduced phosphite toxicity. To control green or blue mold, fruit were inoculated with P. digitatum or P. italicum, then immersed 24 h later in KP, calcium phosphite (CaP), sodium carbonate, sodium bicarbonate, or potassium sorbate for 1 min at 20 g/liter for each at 25 or 50°C. Mold incidence was lowest after potassium sorbate, CaP, or KP treatments at 50°C. CaP was often more effective than KP but left a white residue on fruit. KP was significantly more effective when fruit were stored at 10 or 15°C after treatment compared with 20°C. Acceptable levels of control were achieved only when KP was used in heated solutions or with fungicides. KP was compatible with imazalil (IMZ) and other fungicides and improved their effectiveness. KP increased thiabendazole or IMZ residues slightly. Phosphite residues did not change during storage for 3 weeks, except they declined when KP was applied with IMZ. KP caused no visible injuries or alteration in the rate of color change of citrus fruit in air or ethylene at 5 μl/liter.

This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2013.