Morphological and biochemical responses of selected Ocimum species under drought

Summary Introduction: Drought stress is known to change biochemical activities resulting in altered plant growth and development. Objective: Due to the shortage of research evidence in a certain taxa of basil, it is imperative to examine the relationship between drought stress and morphological changes as well as essential oil accumulation. Methods: An open field experiment was conducted in 2020 to determine the effects of drought stress on the morphological and biochemical responses of selected Ocimum species. Five basil species, namely O. basilicum ‘Genovese’, O. basilicum ‘Ohre’, O. × africanum, O. americanum, O. selloi, and O. sanctum ‘Krishna’ were grown under irrigated (control) and non-irrigated (drought stress treatment) plots with two block replications. Results: The result showed that irrigation had a positive effect on production. Consequently, fresh and dry biomass yields were higher on irrigated plots by 39% and 33%, respectively. No significant changes were detected between the treatments in essential oils (EO) yield and EO composition of major compounds. However, a slight increase in camphor (O. × africanum), nerol (O. americanum), and trans-β-caryophyllene (O. sanctum ‘Krishna’) ratios were observed under irrigation treatments. On the other hand, drought stress increased EO content, polyphenol content, and antioxidant capacity. Furthermore, drought stress had a positive effect on the ratios of 1,8-cineole (O. × africanum), and eugenol (O. sanctum ‘Krishna’). There is only a slight increase in EO content under drought stress, which is not comparable to the significant yield reduction recorded. Morphological and biochemical variations were also detected among basil species. Accordingly, higher biomass (616.33 g/plant) and EO yield (3.72 ml/100 g) among the species were obtained from O. basilicum ‘Genovese’ and O. × africanum, respectively. Conclusion: Irrigation is imperative for maximizing biomass and EO yield of tested basil species.