Starch degradation of detached apple fruit in relation to ripening and ethylene

The physiology of starch degradation in relation to ripening and ethylene was investigated using 'Tsugaru' (early-maturing) and 'Fuji' (late-maturing) apples (Malus domestica Borkh.). Fruits were harvested at immature and mature stages, and treated with ethylene and 1-methylcyclopropene (1-MCP). In immature fruit of both cultivars, starch content rapidly decreased during storage at 25 C, and 1-MCP had little effect on this change. Ethylene treatment slightly stimulated the degradation of starch, but differences in starch among treatments were small. The respiration rate gradually decreased and ethylene production remained low during storage irrespective of the treatments and cultivars. These results showed that fruit at this stage could not respond to endogenous and exogenous ethylene for inducing the climacteric, and starch degradation did not relate to the climacteric or ethylene. In mature 'Tsugaru', 1-MCP treatment significantly inhibited ethylene production and reduced the respiration rate and starch degradation. The effects of 1-MCP and ethylene on starch degradation in mature 'Fuji' were small, and starch content decreased drastically in all treatments, although 1-MCP significantly inhibited ethylene production and the respiration rate. It is suggested that ethylene is partially involved in starch degradation in mature 'Tsugaru', but not in 'Fuji'. These results showed that the role of ethylene in starch degradation differs between cultivars and their harvested stages, relating to ripening and physiological characteristics of the fruit.