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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. [ABSTRACT FROM AUTHOR]

Effect of 2,4-D and naphthalene acetic acid (NAA) on fruit drop reduction in pummelo cv. Thong Dee was investigated in the pummelo growing areas of Nakhon Pathom province, Thailand. Five similar sized and aged of pummelo trees were selected to set up the experiment. Ten mature branches with the same size from each pummelo tree were randomly selected around the canopy for 2,4-D (20 and 40 mg L−1), NAA (20 and 40 mg L−1) application and control. All treatments were applied to selected pummelo branches 2 times at full bloom and 2 months after fruit set. The results showed that 20 mg L−1NAA (14.84%) and 40 mg L−1NAA (12.26%) gave significantly higher percent of fruit retention at 6 months after fruit set. However, leaf total nonstructural carbohydrate concentration analysis showed that 40 mg L−12,4-D (104.86 mg g−1) and 20 mg L−12,4-D (96.55 mg g−1) gave significantly higher total nonstructural carbohydrate than those in control (78.44 mg g−1). For fruit quality, 40 mg L−12,4-D and 20 mg L−12,4-D gave the highest peel weight with 435.55 and 358.57 g, respectively, and 40 mg L−12,4-D gave the highest peel thickness with 20.25 mm, while 20 mg L−1NAA gave statistically higher total soluble solid than those in 20 mg L−12,4-D and 40 mg L−12,4-D. Therefore, 20 mg L−1of NAA sprayed 2 times at full bloom and 2 month after fruit set effectively reduced fruit drop and increased percentage of fruit retention in pummelo cv. Thong Dee. [ABSTRACT FROM PUBLISHER]