Ethylene biosynthesis and related physiological changes in Penicillium digitatum-infected grapefruit (Citrus paradisi)

Abstract

Biochemical and physiological changes and their relation to ethylene biosynthesis were studied in grapefruit (Citrus paradisi Macf. cv. Marsh Seedless) peel, 5–6 days after inoculation with Penicillium digitatum Sacc. In both the albedo and flavedo tissues of the peel, fungal invasion was associated with increases in free galacturonic acid but with reductions in pH and soluble proteins. The extent of the changes was smaller the greater the distance from the maceration front. Two parallel and distinct maceration fronts could be defined in the peel, the one in the albedo preceding that in the flavedo. Fungal glucosamine was present in the apparently healthy region of the albedo up to 15 mm ahead of the flavedo maceration front.

Fungal invasion was associated with increases in both 1-aminocycloproprane-1-carboxylic acid (ACC) and ethylene production but the ability of the tissue to convert ACC to ethylene decreased with the development of the infection. The early relatively low rate of ethylene production in infected fruit seems to originate mostly from the fruit tissue while a later and higher rate of ethylene production originates mostly from the fungus.