Reproductive Biology of Some Gum-Producing Indian Desert Plants

Abstract

This chapter covers the reproductive biology of Acacia senegal, Butea monosperma, Boswellia serrata, Commiphora wightii and Sterculia urens – important gum and gum-resin yielding tree species that grow in the deserts and dry deciduous forests of India. These species have been overexploited and there is a need for conservation of their germplasm to ensure their availability on a sustainable basis. Acacia, Butea and Boswellia bear bisexual flowers. Commiphora exhibits trioecy with predominantly female plants with only two male and one andromonoecious plants out of 1,185 plants scored. Sterculia exhibits cryptic monoecy; morphologically, the plants are andromonoecious with male and bisexual flowers, but the pollen grains in bisexual flowers are sterile. Flowers of Acacia, Sterculia and Boswellia are of generalised type and are pollinated by honey bees, particularly Apis dorsata and A. indica, while those of Butea are of typical bird syndrome and are pollinated by sunbirds and also the three-striped squirrel. No pollination occurs under field conditions in Commiphora and manual pollination does not result in pollen tube growth into the ovary. Boswellia and Butea show typical self-incompatibility. Acacia and Sterculia exhibit late-acting self-incompatibility; although pollen tubes reach the embryo sacs following selfing, no seeds develop. Commiphora exhibits non-pseudogamous apomixis, characterised by degeneration of the egg, adventive nucellar polyembryony and autonomous endosperm formation. Seed set under field conditions is generally low in most of these species. This is partly due to the limiting amount of compatible pollen. In Sterculia and Boswellia, although seeds germinate readily below the canopy of the parent trees, there is hardly any seedling recruitment in forests. The relevance of reproductive features in conservation, and the need for sustainable utilisation of these important species are highlighted.