Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2012
Publication Date: 1/1/2013
Citation: Cerioni, L., Rapisarda, V., Doctor, J., Fikkert, S., Ruiz, T., Fassel, R., Smilanick, J.L. 2013. Use of phosphite salts in laboratory and semi-commercial tests to control citrus postharvest decay. Plant Disease. 97:201-212. Interpretive Summary: Losses of fresh citrus fruit after harvest due to infections by decay fungi can disrupt the marketing of these fruit, particularly when exported to distant but high value markets. Conventional fungicides are commonly applied to fruit to control these fungi, but actions by regulatory agencies, buyers, and consumer groups make the development of alternatives to this practice valuable and that was the purpose of this work. We found that solutions of the chemically simple compound phosphite, which is relatively non-toxic and has very low environmental impacts, have some potential to be used as fresh citrus fruit treatments to reduce postharvest rot losses. This work provides specific information about how phosphites can be used and it is of value to those in the citrus fruit industry that seek alternative to the conventional fungicides used today.
Technical Abstract: EC50 concentrations of potassium phosphite (KP) to inhibit germination 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 Penicillium italicum, then immersed 24 hr later in KP, calcium phosphite (CaP), sodium carbonate, sodium bicarbonate, or potassium sorbate (PS) for 1 min in 20,000 mg/liter of each at 25 or 50 C. Mold incidence was lowest after PS, CaP, or KP treatments at 50 C. CaP was often more effective than KP, but deposits a white residue on fruit. Decay control after KP treatment persisted during storage at 10 C, but diminished at higher storage temperatures. Adequate effectiveness required KP use in heated solutions or with fungicides. KP was compatible with imazalil (IMZ) and other fungicides and improved their effectiveness. KP tended to increase TBZ or IMZ residues slightly. Phosphite residues were stable, 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 5 µl/liter ethylene.