Factors affecting development of disorders expressed after storage of 'Gala' apple fruit

This study investigated factors influencing susceptibility and development of physiological disorders and decay expressed after long-term storage in 'Gala' apple fruit (Malus domestica Borkh.). Five experiments were performed over ten production years with fruit from two environmentally different orchard locations in a humid subtropical climate at 990 m (warmer) and 1415 m above sea level. Fruit were harvested at two maturity stages (early and advanced), treated or not treated with 1-methylcyclopropene (1-MCP) and stored at 0.5 & DEG;C or 2 & DEG;C in a controlled atmosphere (CA, 1.5 kPa O2 and 2.5 kPa CO2), for 240 d plus 7 d shelf life. In one experiment, fruit were stored in CA with CO2 concentrations of 1.5 or 3 kPa. The relationship between fruit mineral composition and physiological disorders was assessed in one production year. Flesh browning (FB) was the predominant disorder, followed by decay, cracking, and lenticel breakdown-wet (LB-wet). The average severity index of lenticel breakdown-dry (LB-dry), leather blotch and bitter pit were low and variable across production years. The FB index was lowest in fruit produced at the colder orchard location, early harvest, treatment with 1-MCP, and storage at 2 & DEG;C. These factors also influenced fruit softening after storage. The major source of variance of the FB index in order of decreasing contribution were harvest maturity, production year, orchard location, 1-MCP and storage temperature. Production year variability of FB index correlated positively with early summer rain and negatively with early spring temperature. A weak positive correlation was also found between FB index and fruit K+Mg/Ca ratio. Higher CA CO2 concentration increased FB in fruit stored at 0.5 & DEG;C but not at 2 & DEG;C. The same factors affected decay, cracking and LB-wet disorder similarly as for FB, except that decay and cracking were not consistently affected by storage temperature, and decay and LB-wet were not impacted by 1-MCP. Storage temperature had the most influence on the variance of LB-wet. LB-dry was highest in late harvest fruit and, in the production year with the highest index, in fruit stored at 0.5 & DEG;C. Leather blotch was highest in early harvest fruit and in fruit stored at 0.5 & DEG;C. 1-MCP treatment did not affect disorders other than FB and cracking. These results suggest that interactions among harvest and postharvest factors influence the development of 'Gala' FB and other disorders and indicate a possible relationship of chilling in FB development. The information may be useful for implementing practical strategies to reduce the development of these postharvest disorders in 'Gala' apple fruit.