Respiratory Response, Ethylene Production, and Response to Ethylene of Citrus Fruit during Ontogeny

The initial respiratory rates at 20 centrigrade of detached oranges (Valencia and navel), grapefruit, and lemons decreased during ontogeny. Small attached oranges respired at the same rate as detached fruits of the same weight, and cutting the pedicel produced no shock or injury stimulus to the respiratory rate. Small oranges and grapefruit (average weight about 15 grams) showed pseudoclimacteric respiratory patterns and produced ethylene. The height of the respiratory rise and the amount of ethylene produced decreased as the fruit increased in weight until the September 4th harvest, when the fruit weights were 120, 64, and 87 grams for grapefruit, Valencia, and navel oranges, respectively; at that time no respiratory rise or ethylene production was observed. The pattern for all subsequent harvest revealed no postharvest rise in the respiratory rates. Lemon fruit, in contrast, had a continuously decreasing respiratory rate at all stages of ontogeny. Exposure to 20 microliters of ethylene per liter induced an increase in the respiratory rate of all varieties at every stage of ontogeny; this was true also in young oranges and grapefruit following their respiratory rise and decline.Evidence is presented that citrus fruits are nonclimacteric fruits.