Experiments were carried out in the greenhouse. Seeds were sown in a cold frame in March, 2012, and plants were transplanted to pots in April when the seedlings had developed 8–10 true leaves. There were 20 replicates for each treatment, one per pot, and the pots were arranged randomly in the greenhouse. The fertilizer and light conditions were kept constant. Fruitlets from the same flowering times were tagged. Four levels of drought stress were used as described previously by Hsiao (1973): 1) normal soil moisture (Control), which is 75–80% of maximum field moisture capacity; 2) light drought stress (LD), 55–60% of field maximum moisture capacity; 3) moderate drought stress (MD), 40–45% of field maximum moisture capacity; and 4) severe drought stress (SD), 30–35% of field maximum moisture capacity. Soil water content was controlled by weight (Lin, 2004).