Breeding and Pollination Biology of Combretum constrictum (Benth) Laws. (Combretaceae)

Abstract

Combretum species possess horticultural attributes. We investigated the phenology, floral morphology, breeding and pollination biology of Combretum constrictum. Visual observation for morphology, day and night monitoring for floral visitors, pollen viability test by the lactophenol cotton blue method, and different pollination experiments were performed on the species. C. constrictum possesses terminal racemes and flowers all year round, with the peak blooming period occurring between August and November. Fruit set predominantly occurs from August to December. The average lifespan of an inflorescence, as observed in the species, is 32 days, while the lifespan of a single flower is 7–12 days. Anthesis is diurnal, proceeds centripetally and lasts approximately 5 h. The average viability of the pollen was 97.05 % on Day 1, decreasing to 11.64 % on Day 4. Visitors from ten families {Dolichoderinae, Hymenoptera (Formicidae), Muscidae, Nectariniidae, Drosophilidae, Tettigoniidae, Acrididae, Hesperiidae, Achatinidae and Myrmicinae} were encountered on flowers of the species during the study period. Five of these visitors, including Cinnyris venustus, Meranoplus bicolor, Camponotus consobrinus and Technomyrmex sp., are the main pollinators of the species. These pollinators predominantly visited the flowers for a few hours until the opening of the flower buds and continued visiting the flowers until 2 days after the opening of the last flower bud on the inflorescence. The flowers are unscented but are brilliant red-pink, suggesting that the visitors/pollinators are attracted to the flowers due to their colour. After pollination, the number of immature fruits in this species ranged from 6 to 51, and averaged 25.80. The percentage of fruit set and mature fruits per inflorescence varied from one treatment to another (self-pollinated, 2.60 ± 1.10; hand cross-pollinated, 4.55 ± 1.43; and visitor-pollinated, 8.75 ± 2.65). These findings indicate that C. constrictum is self-compatible, but the presence of pollinators increases the number of fruits and probably enhances the fertility of the fruits. The species exhibits entomophily (insect pollination) and ornithophily (bird pollination) syndromes.