Hormonal Approaches for Enhancing Flowering Intensity and Fruit Set in Kola, Cola nitida (Vent.) Schott. & Endl.

Kola—Cola nitida (Vent.) Schott. & Endl.—is a tropical nut crop of social and economic importance. The crop is threatened by low yield due to sexual incompatibility. The search for sexually compatible varieties is ongoing. However, efforts are constrained by bottlenecks of irregular and erratic flowering in kola. Growth hormones have been reported to enhance flowering intensity in plants. Little is known about the modifying effects of growth hormones on flower induction and their residual effect on pod set and nut quality in kola. This study aimed to investigate the effects of growth hormones on flowering, pod set, and nut quality under field conditions in two production environments in Ghana. Three hybrids (A2 × JB1, B1/149 × B1/151, and GX1/31 × GX1/42) of a progeny trial located at Bunso and Afosu were used for the study. Three growth hormones (gibberellic acid, asparagine acid, and glutamic acid) were tested, while sterile distilled water was used as the control. The treatment of a branch of the three hybrids of kola consisted of gibberellic acid (6 mM, 9 mM, and 12 mM), asparagine acid (6 mM, 9 mM, and 12 mM), glutamic acid (6 mM, 9 mM, and 12 mM), and sterile distilled water. Five stands of each genotype were treated once with 200 mL of respective plant growth hormone using a 1‑L plastic spray bottle. Early in the morning, an entire branch per plant was sprayed, covering the leaves, stems, and meristems. The four hormonal treatments including distilled water as a control, three hormone concentrations, three kola hybrids, and two field locations were arranged in a 4 × 3 × 3 × 2 factorial experiment using a randomized complete block design with three replications. At 5 months after the hormone treatment, data were collected on the number of flowers, fruit set, nut yield, and quality attributes for the 2021/2022 season. To determine the residual effects of the hormones, the same dataset was collected in the 2022/2023 season. There were significant (P < 0.05) effects of gibberellic acid, glutamic acid, and asparagine acid on flowering and fruit set of kola. A higher number of flowers and fruit set and an enhanced Brix content were observed for kola nuts from branches treated with gibberellic acid, glutamic acid, and asparagine acid as compared to the control. The results show that growth hormones, especially gibberellic acid and glutamic acid, may be used to enhance flowering intensity and fruit set in kola.