A comparison of preharvest and postharvest ethylene production and respiration rates of saskatoon (Amelanchier alnifolia Nutt.) fruit during development

Abstract

Changes in respiration and ethylene production rates of nine maturity classes of saskatoon (Amelanchier alnifolia, Nutt.) fruit after harvest were compared with those of fruit maturing and ripening on the plant. During ripening on the plant, ethylene production increased on a whole-fruit and fresh-weight basis, while respiration increased substantially on a whole-fruit basis but remained constant on a fresh-weight basis. Fruit harvested at the greenish yellow to pink stages (maturity classes four and five, respectively) increased their ethylene production until 15-20 h after harvest, and this was coincident with ripening to maturity class seven and thus a color change to red. Ethylene production then declined over the next 15 h. Respiration rates of harvested immature, mature, and ripe fruits declined over 5 days, except for a relatively brief 8-12% rise starting 15-20 h after harvest. This brief increase in respiration was characteristic of fruit of all maturity classes, likely reflecting a wound response associated with harvest rather than a ripening-induced change in metabolism. Continuous treatment of attached or detached fruit with propylene or ethylene in an open airflow system did not induce an increase in respiration earlier, relative to control fruit. The respiratory response of saskatoon fruit during postharvest ripening was thus very different from that of fruit that ripened on the plant. Thus, the increase in respiration associated with ripening could only be demonstrated on a whole-fruit basis if fruit remained on the plant. Preharvest and postharvest changes in ethylene production during ripening also differed but were both consistent with climacteric ripening.Key words: Amelanchier alnifolia, ethylene, ripening, saskatoon fruit.