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Penicillium digitatum-infected grapefruit synthesize large quantities of the stress hormone ethylene. The compound 1-methylcyclopropene (1-MCP) inhibits the binding of ethylene to the ethylene receptor site, the ethylene binding protein (EBP). Treating infected fruit with 1-MCP prevented infection-induced degreening, such that fumigated fruit retained their green immature color compared to yellow non-fumigated controls. However, 1-MCP treatment significantly increased whole fruit ethylene production. In flavedo tissue of infected non-1-MCP treated fruit, 1-aminocyclopropane-1-carboxylate (ACC) synthase transcript accumulation, ACC synthase (ACS) enzyme activity, ACC and ethylene synthesis were all significantly higher +5 mm ahead of the lesion front than in uninfected non-1-MCP treated controls, but decreased significantly with increased sampling distance away from the lesion. 1-MCP treatment increased …