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Development of Green Mold in Degreened Oranges. G. Eldon Brown, Plant Pathologist III, Florida Department of Citrus, University of Florida, IFAS, Agricultural Research and Education Center, Lake Alfred 33850; Phytopathology 63:1104-1107. Accepted for publication 27 February 1973. DOI: 10.1094/Phyto-63-1104.

The incidence of green mold caused by Penicillium digitatum is reduced by degreening oranges at relative humidities of 90-96% at 30 C. Degreening for 2 or 3 days at these high relative humidities induced lignin formation in injured flavedo tissue. Lignification rendered the injuries less susceptible to infection by P. digitatum. No lignification occurred where injured fruit were degreened at relative humidities of 55-75% at 30 C, and consequently the fruit were much more readily invaded by this fungus. Degreening at 90-96% relative humidity at 27 C did not reduce infection by P. digitatum as effectively as degreening at 30 C. Injuries with severe peel oil damage were usually invaded by P. digitatum even when the injured fruit were degreened at 90-96% relative humidity. The oil killed many of the cells surrounding the injury and thereby prevented lignification. P. digitatum usually invaded deep injuries which exposed albedo cells that never synthesized lignin during degreening. Fruit with desiccated flavedo or albedo injuries were not invaded by P. digitatum. Infection did occur, however, when these fruit were packed in consumer packages, especially polyethylene bags, where a rapid buildup of relative humidity provided moisture for spore germination. However, less green mold developed where the fruit injuries had lignified.

Additional keywords: Citrus sinensis, ethylene, postharvest decay, wound healing.