Pollination biology, breeding system and reproductive success of Adhatoda vasica, an important medicinal plant

Abstract

Adhatoda vasica Nees. (Acanthaceae) is an important and widely used medicinal plant. The flowers last for 3-5 days, they are protandrous and pass through three distinct phases: male, bisexual and female. Two species of carpenter bees, Xylocopa verticalis and Xylocopa sp. are the effective pollinators. Pollen grains are deposited on the dorsal surface of the thorax during Xylocopa visit to the flowers in the male phase, and the stigma rubs the pollen-coated thorax and is pollinated when the bees visit the flowers in bisexual and female phases. There is a high level of geitonogamy. Pollination efficiency under field conditions is high (95%). However, fruit set is poor (6%). The species is self-incompatible. None of the self-pollinated flowers sets fruits, but over 50% of the cross-pollinated flowers sets fruits. The results indicate that protandry does not prevent selfpollination, but reduces interference in export and import of pollen. Although the flowers have adapted well to achieve a high level of pollination, reproductive success in terms of fruit set is low, largely due to the limitation of compatible pollen.