Pollination biology of large cardamom (Amomum subulatum)

Abstract

Amomum subulatum Roxb. (family Zingiberaceae) is the large cardamom of commerce cultivated in tropical wet evergreen forests of the Eastern Himalayas of India, Nepal and Bhutan. This study seeks to identify floral visitors and pollinators, examine floral adaptations for pollination and evaluate pollination efficiency. Studies were carried out in two flowering seasons (2005, 2006) in a 6-ha plantation located adjacent to a degraded reserve forest in the Sikkim part of the Himalayas. Only two flower visitor species, a bumble-bee (Bombus haemorrhoidalis Smith) and a honey bee species (Apis cerana F.) were recorded. The bumble-bee was the effective and only pollinator, but A. cerana was the pollen robber. Major flower adaptations for pollination by the bumble-bee are the length of the nectar tube, which is not accessible to short-tongued bees and a narrow passage in the fresh flower between the anther-stigma column and the labellum. The narrow passage forces the bumble-bee to push the anther-stigma column to enter the flower, which brings the body of the bumble-bee in contact with the anther and the stigma, and effects pollination. A. cerana does not come in contact with the stigma during pollen foraging and hence is unable to bring about pollination. Thus, structural features of the flower of A. subulatum differentiate the pollinator and the pollen robber. Pollination efficiency in the plantation was low due to the low population density of wild native pollinator, B. haemorrhoidalis.