Control of citrus postharvest decay by ammonia gas fumigation and its influence on the efficacy of the fungicide imazalil

Authors: MONTESINOS-HERRERO, CLARA - Valencian Institute For Agricultural Research; Smilanick, Joseph; Tebbets, John; Walse, Spencer; PALOU, LLUIS - Valencian Institute For Agricultural Research

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/24/2010
Publication Date: 1/1/2011
Citation: Montesinos-Herrero, C., Smilanick, J.L., Tebbets, J.S., Walse, S.S., Palou, L. 2011. Control of citrus postharvest decay by ammonia gas fumigation and its influence on the efficacy of the fungicide imazalil. Postharvest Biology and Technology. 59(1):85-93.

Interpretive Summary: A large portion of fresh citrus fruit rot after harvest unless measures are taken to control this problem. We evaluated ammonia gas treatment of the fruit and found it effectively stopped the rot and it improved the performance of a common preservative already used to manage this problem, allowing much lower rates of it to be used. The practices we introduce in this work prolong the shelf and shipping life of fresh citrus fruit which improves returns to growers, while increasing the supply and decreasing the prices of fresh citrus fruit for consumers, and it extends the storage life of the fruit in consumers refrigerators.

Technical Abstract: The most important citrus postharvest diseases of arid citrus production areas, green mold and blue mold, caused by Penicillium digitatum and P. italicum, respectively, were effectively controlled by fumigations with ammonia alone at 3000 to 6000 µl/liter or at 1500 µl/liter when applied to fruit pretreated with very low doses of imazalil. Fumigations with two injections of 3000-µl/liter ammonia, separated by 2 h and maintained for 6 h at 22ºC effectively reduced the incidence of both diseases. The effectiveness of treatments with imazalil at rates of 10 or 30 mg/liter followed by ammonia fumigation was always additive and sometimes synergistic. Ammonia had a toxic effect on conidia and increased the pH within wounds in the fruit rind, which retarded the growth of the pathogens and increased the toxicity of imazalil. When combined with ammonia fumigation, imazalil was effective at rates that were less than 10% of typical commercial rates. Ammonia at effective doses did not visibly harm the fruit or leave detectable residues on the treated oranges and lemons. Ammonia treatments could be applied within modified ethylene degreening chambers and augment or replace synthetic fungicides in citrus postharvest decay management. The capacity of ammonia to control imazalil resistant isolates of P. digitatum, which occur commonly in citrus packinghouses, is particularly valuable.