Reproductive Biology of Vitex doniana (Black Plum) in the Northern Guinea Savanna of Plateau State

Vitex doniana (black plum) is a multipurpose savanna tree of nutritional and economic importance across North Central Nigeria, yet its reproductive biology in Plateau State's Northern Guinea Savanna remains undescribed, limiting domestication and propagation efforts. This study investigated the reproductive biology of Vitex doniana at three sites in Barkin Ladi and Mangu Local Government Areas of Plateau State. Phenological observation of leaf flush, flowering, and fruiting was conducted at monthly intervals over one year. Floral morphology, floral visitors, fruit set, and seed dispersal mechanisms were characterised through field observation and laboratory analysis. Controlled pollination experiments (open pollination, self-pollination, and hand cross-pollination) were conducted to determine the mating system. Phenological observation revealed that flowering occurred from February to April, coinciding with the late dry season. Inflorescence morphology confirmed zygomorphic bisexual flowers. The most frequent floral visitors were Apis mellifera and Xylocopa species. Open-pollination fruit set (34.2%) was significantly higher than self-pollination fruit set (8.7%), confirming predominant cross-pollination. Seeds were primarily dispersed by frugivorous bats and birds. Seed germination under nursery conditions was 67% after soaking in hot water for 10 minutes. The study concludes that Vitex doniana is primarily an outcrossing species dependent on bee pollinators, and recommends managed bee placement near cultivation sites to improve fruit set in any domestication programme in Plateau State.

Keywords: Vitex doniana, reproductive biology, pollination ecology, Northern Guinea Savanna, Plateau State