Polination biology of Afgekia sericea Craib

Abstract

Afgekia sericea Craib is an endemic species of Thailand and becoming rare due to nature habitats disturbed and very low percentage in the range of 1-3% of fruit setting. The study was conducted thus to investigate the pollination biology to explain why fruit setting is so low. It was found that inflorescences are produced from April to October and each inflorescence lasts about 2 months. SEM investigation revealed that floral structure developed acropetally. Flowers anthesis begin from 4:00 hour and last only one day. The maximum pollen viability is 90% as revealed by tetrazolium test, but 68% was able to germinate in vitro and viability abruptly decreased after 24 hours. According to localization of esterase, the stigma receptivity occurs in the same period of time of anthesis. Nineteen insects and one bird species were found to be visitors but only twelve might take part in the pollination, of which Megachile velutiana Smith is likely a main pollinator for A. sericea. These insect visitors are attracted by nectary guides on the vexillum and rewarded by pollen and/or nectar. The nectar is produced by secretary cells in the collar disc around the gynoecium. From HPLC analysis, the nectar is composed mainly of sucrose. Bagging experiments yielded no fruit setting. In addition, open pollination that allowed insect to visit flowers, resulted in fruit setting. Furthermore, distance between individual plant may affect the success of fruit setting, i.e. the close of plants, the more fruit setting. It might be then concluded that A. sericea is likely cross-pollinating species and is self-incompatible. Thus, possible causes of low fruit setting might be existence of self-incompatibility and young fruit abortion.