Flower and fruit aba, IAA and carbohydrate contents in relation to flower and fruit drop on Mangosteen trees

Mangosteen (Garcinia mangostana L.) is the major exported fresh fruit of Indonesia. Mangosteen productivity in Indonesia was about 30-70 kg/tree, lower than Malaysia and India which is about 200-300 kg per tree. The low productivity of mangosteen in Indonesia is mainly caused by low fruit harvest per tree due to excessive abscission of fruits and flowers. The causes of this abscission of flowers and fruit is not known. Consequently, there are no recommendations for field methods to correct this problem. The research was conducted to study the content changes of ABA, IAA, and carbohydrate in relation to abscising flower and fruit of mangosteen trees. The research was conducted in Mekarsari Fruit Garden, Bogor, using 40 mangosteen trees aged 10 years old. ABA and IAA content in abscised fruits and flowers were compared to those of attached fruits and flowers. Further, the carbo-hydrate content (total sugar) analyzed from the terminal leaves of shoots with abscised flowers and fruits were compared with the terminal leaves of shoots with attached flowers and fruits. The abscised flowers and fruits had a high ABA content, low IAA, and low supply of photosynthate (low total sugar content in the leaf tissue). The ABA content in abscised flowers and fruits (22.5 ng/g dry weight for flowers and 31.8 ng/g dry weight for fruit) was significantly higher than the ABA content in attached flowers and fruits (6.7 ng/g dry weight for flowers and 13.4 ng/g dry weight for fruit). The IAA content in abscised flowers and fruit (5.4 ng/g dry weight for flowers and 0.83 ng/g dry weight for fruit) was significantly lower than the IAA content in attached flowers and fruit (8.80 ng/g dry weight for flowers and 6.43 ng/g dry weight for fruit). The carbohydrate content (total sugar) in leaves of shoots with abscised flowers and fruit (40.3 and 52.3 mg/g dry weight of leaf) was lower than that of leaves on shoots with attached flowers and fruit (41.2 and 59.1 mg/g dry weight of leaf). Based on these results, application of synthetic IAA accompanied by adopting good agriculture practices are recommended to prevent mangosteen flowers and fruit abscising.