Potting media and seed pre-sowing treatments influencing emergence and early seedling growth of bitter kola (Garcinia kola Heckel) under humidity chamber environment

Abstract

Despite the enormous socioeconomic and therapeutic potentials of bitter kola (Garcinia kola Heckel), organized cultivation of the species is still very rare, owing to the scarcity of the seedlings predicated on seed dormancy challenges. This study aims to develop a workable protocol for seed germination of bitter kola using four growth media [including rice husk (RH), sawdust (SD), river sand (RS) and a soilless medium RH³:PM²:SD¹ formulated in volume ratios of RH, poultry manure (PM), and SD]; and five seed pre-sowing treatments [decortication by coat removal, soaking seeds in water for 24 h, 48 h, or 72 h; plus the untreated control seeds]. Seedling emergence and early growth of bitter kola were studied across the treatments in factorial combinations under a humidity growth chamber in a completely randomized design (CRD) replicated in three plastic baskets containing 10 seeds each. Results showed that seedling emergence was significantly (p < 0.05) earliest in RH³:PM²:SD¹ (69 days) and RS (74 days), followed by SD (81 days), and the latest in RH (104 days). Percentage emergence was high and statistically similar in RS (95.3%), SD (90.0%), and RH³:PM²:SD¹ (86.8%) but significantly (p < 0.05) poor in the RH (55.9%) medium. The earliest seedling emergence was recorded in 49 days with the decorticated seeds sown in RS medium. Decorticated seeds with the 48 h and 72 h pre-soaked seeds recorded 100% emergence in RS. The decorticated seeds also had 100% emergence in SD and RH³:PM²:SD¹. Seeds pre-soaked for 48 or 72 h and raised in RS produced the tallest seedlings. Across the seed treatments, seed decortication and the 48 and 72-h soaking durations significantly (p ≤ 0.05) produced seedlings with the highest number of leaves. Similarly, RS, SD and the soilless medium RH³:PM²:SD¹produced seedlings with a greater number of leaves compared to the RH medium. For prompt germination of bitter kola seeds with vigorous seedling growth, seed decortication or soaking for 48–72 h are the recommended pre-sowing treatments. Regarding the potting media, river sand gave the best results (in terms of emergence and early seedling growth); however, sawdust and the soilless nursery mix (RH³:PM²:SD¹) are equally good for raising bitter kola seedlings under a warm humidity growth chamber. The use of high humidity growth chamber– a miniature greenhouse is a simple technology which can easily be adopted by local and peri urban farmers in commercial propagation of bitter kola.