Watercore disorder in Japanese pear ‘Niitaka’ is increased by high fruit temperatures during fruit maturation

• We investigated the effects of temperature on watercore incidence in Japanese pear.
• Temperatures around ‘Niitaka’ fruits were increased using electric heating coils.
• High temperature during fruit maturation statistically increased watercore occurrence.
• High temperature also affected other parameters of fruit quality.
• Shade hat treatment only slightly reduced temperature and watercore incidence.

We investigated the effects of fruit temperature on the incidence of watercore in Japanese pear ‘Niitaka’. To increase the temperatures in the environments of maturing fruit, we fixed electric heating cables around the fruit during the maturation period (6–3 weeks before estimated harvest date). This treatment increased the average temperatures, the daily minimum temperatures, and the daily maximum temperatures by 1.4–2.5 °C, 1.5–2.8 °C, and 0.8–1.7 °C, respectively. The incidences of watercore were statistically increased by heat treatment (P < 0.01). In particular, the incidences of watercore in heated fruit were almost twice those of untreated fruit in Ibaraki in 2008 and Kumamoto in 2009. Furthermore, the fruit treated with higher temperatures showed increased flesh firmness, soluble solids contents, and pH at harvest, although the interactions (treatment × place/year) were also significant. These results imply that parameters of fruit quality, including the occurrence of watercore, are affected by the temperature of fruit during maturation, and that high temperatures give rise to watercore. Accordingly, we attempted to reduce the maximum daily fruit temperatures by putting shade hats over the fruit to see if this would reduce the incidence of watercore. Shade hat treatment decreased the daily maximum temperature by 0.5–2.2 °C during maturation without significantly altering the mean and daily minimum temperatures. Watercore incidence was reduced by shade hats in all experiments, however, the effects were not statistically significant. The temperatures in the tested years were very high, with mean and daily maximum temperatures around control fruit of over 28 °C and 34 °C, respectively. The results of this study suggest that shade hat treatment may not be enough to decrease temperatures around fruit and reduce the incidence of watercore.