Fruit Growth, Fruit Carbohydrate Concentration and Fruit Nutrient Concentration in Dropped Pummelo (Citrus grandis(L.) Osbeck) Fruit cv. Thong Dee

The research was conducted in the pummelo growing areas of Thailand. The results showed that the dropped fruits had a statistically smaller fruit size (7.25 cm) than the retained fruit (9.35 cm; P < 0.05) at 4 months after fruit set. Moreover, the dropped fruits had an abnormal fruit shape when compared to the retained fruits. Consideration of fruit and leaf carbohydrate concentrations showed that the retained fruits had statistically higher carbohydrate concentrations (262 mg g−1) than the dropped fruits (203 mg g−1; P < 0.05). Meanwhile, the dropped fruits had statistically lower leaf carbohydrate concentrations (55 mg g−1) than those in the retained fruits (85 mg g−1; P < 0.05). The retained fruits also had statistically higher N, P, and K concentrations (1.6%, 1.1%, and 1.3%, respectively) than the dropped fruits (1.1%, 0.5%, and 1.0%, respectively; P < 0.05). Therefore, the causes of early fruit drop in pummelo could be insufficient carbohydrate and plant nutrients supplied for fruit growth and development.