Modulating postharvest apple fruit physiology by managing the harvest date and 1-MCP application

The effect of harvest timing on postharvest ripening was investigated by changes in ethylene production, expression of ethylene biosynthesis genes MdACS1 , MdACS6 , (1-aminocyclopropane-1-carboxylic acid synthase 1 and 6) and the ACS degradation promoting gene MdETO1 (Ethylene overproducer 1). Apple fruit of two cultivars, ‘Red Aroma’ and ‘Rubinstep’, were harvested at three time points, early, middle, and late, at two-week intervals. Fruit were either treated with 1 ppm 1-Methylcyclopropene (1-MCP) or remained untreated, and stored at 4 °C in regular atmosphere. Late harvested, untreated apples reached peak ethylene production after the shortest time in cold storage ('Red Aroma' in week five, 'Rubinstep' in weeks nine and ten), while early harvested, untreated fruit reached their peak after a longer time ('Red Aroma' in week eight, 'Rubinstep' in weeks 13 and 14). Early harvested fruit experienced greater firmness loss and a higher increase in SCC/TA ratio during cold storage. Senescence in late harvested, untreated fruit was evident from low ethylene production after simulated shelf-life and increased physiological disorders in ‘Rubinstep’. In 1-MCP-treated fruit, ethylene production increased toward the end of storage, particularly in early harvested fruit, indicating a decline in 1-MCP efficacy over time. Gene expression analysis showed strong induction of MdACS1 during climacteric ripening. MdETO1 positively correlated with MdACS1 gene expression, suggesting positive co-regulation. The expression of MdACS6 was negatively correlated with simulated shelf-life and with 1-MCP treatment, suggesting regulation by temperature and metabolic state. Overall, harvest timing and 1-MCP strongly influenced the changes in fruit physiology during postharvest storage. • Harvest timing affects postharvest physiology of apple fruit in a Nordic climate. • Expression of MdACS6 was induced by cold storage and reduced by 1-MCP treatment. • MdETO1 expression correlated with MdACS1 , suggesting likely positive co-regulation.