Reproductive biology of Azadirachta indica (Meliaceae), a medicinal tree species from arid zones

Abstract

AbstractNeem or the Margosa tree, Azadirachta indica (Meliaceae), is a versatile tree species common in arid zones. We investigated the reproductive biology of Neem, including phenology, floral biology, pollination ecology and the breeding system, in three natural populations in northern India. Phenological observations established that trees within a population flowered synchronously, but populations varied in the time of onset of flowering; a few trees flowered twice a year. An inflorescence bears ∼ 91 bisexual, white and sweet‐scented flowers. The stigma consists of a non‐receptive apical region and a subjacent rim of receptive surface; papillae on the two regions differ in their morphology and function. The occurrence of natural pollination both by wind and insects indicates ambophily. Insect pollinators were predominantly represented by Hymenoptera and Lepidoptera; Apis spp. were the most effective pollinators. Although the occurrence of incomplete dichogamy and a pollen : ovule ratio of ∼ 627 indicates the possibility of autogamy, supplemental pollinations clearly established that the trees were 100% self‐incompatible and incompatibility is regulated at the gametophytic level. Natural fruit set was low (∼ 5%) and hand cross‐pollinations increased the fruit set to ∼ 19%. Our study demonstrated that natural fruit set in Neem is possibly limited by insufficient amounts of xenogamous pollination and resources.