Floral and Pollen Traits of Moringa oleifera Lam. and Moringa peregrina (Forssk.) Fiori Provide Reproductive Adaptations for Arid Conditions

Abstract

Our study attempted to elucidate the significance of floral and pollen traits of the highly nutritious tropical trees Moringa oleifera and Moringa peregrina for their reproductive success under arid conditions. We found that the pollen grains of both species were immersed in a pollenkitt that constituted ~ 60% of the pollen. Successful pollination was achieved by large bees inserting the pollen into a narrow stylar tube. We found that, upon removal of the pollenkitt, approximately 65% fewer pollen grains penetrated the stylar tube for both species. The pollenkitt protected against heat and desiccation, while removing the pollenkitt resulted in significantly reduced levels of the viability of pollen grains, especially in M. oleifera, and significantly reduced levels of germinability in both species. The stylar tube provided high protection for pollen grains against heat and desiccation even when the pollenkitt was removed. Chemical analysis of pollenkitts of the two species revealed a waxy blend of 21 hydrocarbon compounds, in which n-alkanes constituted > 90% of the compounds and their identity corresponded to known plant and animal hydrocarbons, associated with protection against heat and water stress. We concluded that, under arid conditions, the reproductive success of both Moringa species is potentially enhanced by their unique floral and pollen traits. This supports the prospect of cultivating M. oleifera and Moringa peregrina as food crops in arid regions across the globe.