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  • Author or Editor: Fernando Alferez x
  • Journal of the American Society for Horticultural Science x
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Several citrus cultivars including `Marsh' grapefruit (Citrus paradisi Macf.) and `Fallglo' tangerine [Bower citrus hybrid (C. reticulata Blanco × C. reticulata × C. paradisi) × Temple tangor (C. reticulata × C. sinensis L. Osbeck)] are prone to develop postharvest peel pitting at nonchilling temperatures. This disorder is characterized by depressions in flavedo that ultimately affect oil glands. Although the fundamental cause for this disorder has not been well defined, increasing evidence indicates that alteration in peel water status during postharvest handling of fruit plays a major role. `Fallglo' tangerines developed postharvest peel pitting when transferred from low (30%) to high (90%) relative humidity (RH) storage. To determine the number of hours of dehydration prior to storage at high RH sufficient to induce peel pitting in `Marsh' grapefruit and `Fallglo' tangerines, fruit were exposed to low RH conditions for increasing periods of time and then washed, coated with commercial shellac-based wax, and stored at high RH. Only 2 hours of low RH storage were sufficient to induce peel pitting in `Fallglo' and `Marsh' after transfer to high RH. The severity of pitting in `Fallglo' tangerines was greater than in `Marsh' grapefruit. Weight loss of fruit at the end of low RH storage and peel pitting after 3 weeks of storage at high RH were significantly correlated. RH conditions in the field at the time of harvest affected susceptibility to peel pitting in both cultivars. Peel pitting was more severe when fruit were harvested at low field RH than high field RH when followed by treatments that induce peel pitting. The data suggest that harvesting susceptible cultivars at high RH, and minimizing exposure to low RH after harvest, could reduce the commercial impact of postharvest peel pitting.

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1-MCP is a gaseous ethylene binding inhibitor that controls or delays ethylene-related postharvest problems in a range of horticultural commodities. Our previous work demonstrated that exposure of calamondin to 1-MCP 16 hours before canopy sprays of ethephon greatly reduced unwanted leaf drop while only partially inhibiting the ability of ethephon to cause fruit loosening. The objective of this work was to determine whether formulated 1-MCP (SmartFresh) could be used in the field to stop defoliation caused by abscission agent applications without significantly altering abscission agent-induced fruit loosening. Spray solutions containing 400 mg·L-1 ethephon with 0, 1, 2.5, and 5 mm 1-MCP were applied to canopies of `Hamlin' and `Valencia' (Citrus sinensis). Timing of 1-MCP applications was a) 24 hours before, b) in combination with, or c) 24 hours after ethephon. Ethephon at 400 mg·L-1 significantly reduced fruit detachment force (FDF) but caused >70% leaf drop within 15 days after application in both cultivars. Applications of 1-MCP reduced ethephon-associated leaf abscission but had little effect on the ability of ethephon to reduce FDF. Timing of 1-MCP applications did not affect the ability of ethephon to cause fruit loosening; however, the best consistent treatment for control of leaf drop was achieved with the combined application of 5 mm 1-MCP and 400 mg·L-1 ethephon. 1-MCP was used in combination with the abscission agents coronatine, methyl jasmonate (MeJa) and 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP) to determine its effect on leaf drop and fruit loosening. Leaf drop in trees treated with ethephon, coronatine, and MeJa was reduced by addition of 1-MCP. However, fruit loosening was largely prevented when 1-MCP was used in combination with coronatine or MeJa. Like ethephon, CMNP-induced fruit loosening was not affected by 1-MCP. The results demonstrate the ability to control ethephon-induced leaf abscission without affecting mature fruit loosening by targeting ethylene binding in citrus.

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