Floral and reproductive biology of Moringa oleifera (Moringaceae) in Burkina Faso, West Africa

Moringa oleifera is a multi-purpose tree with a high potential to be grown and utilized also in West Africa. Since there hardly exist any ecological studies regarding moringa in West Africa we aimed to examine the floral and reproductive biology of the species. In 2014, field work was conducted in South-West Burkina Faso. Flower visitors were observed for a total of 144 h, and the anthesis of 20 flowers was studied during the course of 7 days. To examine the reproductive system of the species, the pollen/ovule (P/O) ratio was determined and 3735 flowers were subjected to different pollination treatments. Whereas sunbirds have been observed as active pollinators in Asia, at our study site, honeybees and carpenter bees visited the flowers frequently, touching anthers and stigma. Hence, they are considered as potential pollinators. Though stingless bees were the most frequent visitors, their pollen collecting behavior and small body size did not provide sufficient evidence to decide if they act as nectar robbers or could be considered as valuable outcrossers. The breeding system of moringa was classified as facultative allogamous due to a P/O ratio of 1320. The pollination experiments also suggest facultative allogamy, which is in line with other studies reporting a mixed mating system of moringa with the ability of self-pollination. However, due to very low fruit set resulting from the experiments, this could not yet be verified. Extremely low fruit set rates of 1.5% in the dry and 0.31% in the rainy season have been observed. In addition, since moringa is not native to Africa, it is likely to have relatively low genetic diversity there, resulting in inbreeding depression and thus low fruit set. Further research is needed to determine whether abiotic resources (water, soil quality), available pollination services or low genetic variability are the key-factors restricting Moringa oleifera pod-yield in West Africa.