Energy-Saving Night Temperature Regime for Satsuma Mandarins (Citrus unshiu Marc.) Grown in a Plastic House with Heating. I. Effect of Temperature and Water Condition on Fruit Growth and Quality

In this study, we discussed how temperature and other environmental factors affect the fruit growth and quality of Satsuma mandarin grown in a plastic house with heating. At 14–23°C, the average nighttime air temperature was positively correlated with the standardized fruit growth rate (GRFSt) in the young stage. In contrast, GRFSt was clearly depressed with a daytime air temperature at around 30°C, and the optimum air temperature for active fruit growth was 25°C. Moreover, in the middle and mature stages, the air temperature did not correlate with the GRFSt. These results indicate that, in the young stage, the air temperature should be controlled at around 25°C during the daytime and 20–23°C during the nighttime for active fruit growth. In the middle and mature stages, fruit growth might not require nighttime air temperatures that are as high as 20–23°C. The air temperatures did not correlate with the fruit soluble sugar content (SSC); in contrast, a close relationship was found between the predawn xylem water potential (ΨXy) and SSC. The day temperature, radiation and ΨXy were linearly correlated with the fruit titratable acidity (TA) in the young stage.