The Lack of a Respiratory Rise in Muskmelon Fruit Ripening on the Plant Challenges the Definition of Climacteric Behaviour

A burst in respiration coincident with fruit ripening has been used for over half-a-century to classify harvested fruit such as apples, bananas, melons, and tomatoes as climacteric. In contrast, respiration slowly declines in harvested non-climacteric fruit such as citrus and strawberries. Autocatalytic ethylene production was later recognized as accompanying the ripening of climacteric fruit. We developed a procedure to insert sterile ports in netted muskmelon (Cucumis melo var. Reticulatus Naud.) fruit to allow repetitive sampling of internal gases in both attached and detached fruit as they ripened. Detached fruit produced the characteristic climacteric pattern of carbon dioxide and ethylene production as they ripened. In contrast, fruit ripening attached to the plant did not exhibit the climacteric increase in respiration, despite a climacteric increase in the plant hormone ethylene. A respiratory rise was observed with fruit ripening on the plant, but only after they abscised. The climacteric burst in respiration, which has been widely observed with ripening, harvested fruit, may be an artifact of harvest and not a natural phenomena associated with ripening of climacteric fruit. The peak in ethylene production by ripening, climacteric fruit, whether harvested or not, might provide a more reliable criterion for separating climacteric from non-climacteric fruit.