Abstract
The effect of preharvest fruit temperature on fruit maturity, sugars, and watercore occurrence was investigated in watercore-resistant ‘Tsugaru’ apples (Malus pumila Mill. var. domestica Schneid.) . Watercore appeared at 35/27°C (day/night) in 1990 and at 33 and 38°C in 1991, although a significantly higher watercore rating was observed only at 38°C. Fruit subjected to a 38°C preharvest temperature had higher specific gravity and lower weight than at other lower temperatures in 1991. Fruit maturity judged by ethylene evolution was advanced at 25/17°C more than at other temperatures in 1990 while the influence of fruit temperature on fruit maturity was not obvious in 1991 because all fruit were picked earlier than intended due to the high temperature injury observed at 38°C. Apples at 35/27°C and 38°C showed the lowest starch content in both inner and outer flesh tissue and fruit at 38°C also had the highest soluble solids content (SSC) and total sugars. Fruit at 35/27°C in 1990 and at 33 and 38°C in 1991 had higher glucose and sorbitol and lower sucrose content than at lower temperatures. The results suggest that high fruit temperature above 35°C induces watercore via the rapid starch breakdown and the accumulation of glucose and sorbitol in ‘Tsugaru’ apples.
