Improvement of yield and phytochemical attributes of Madagascar periwinkle varieties by L- cysteine and melatonin foliar application

Catharanthus roseus (L.) G. Don, commonly known as Madagascar periwinkle and belonging to the Apocynaceae family, possesses notable medicinal properties within its leaves, roots, and flowers. This study aimed to explore the influence of exogenously applied melatonin and L-cysteine on the yield and phytochemical profile of Catharanthus roseus (L.) G. Don. Employing an experiment on factorial test within a completely randomized design, we investigated three C. roseus varieties (“alba,” “roseus,” and “ocellatus”) as the first factor, along with various concentrations of melatonin (MT) (0, 100, 200, and 400 µM) and L-cysteine (L-cys) (0, 200, 400, and 800 µM) as the second factor. Results revealed substantial enhancements in morphological traits, with a significant increase in dry yield observed for MT (400 µM) and L-cys (800 µM) treatments, displaying increments of 72.86 and 62.79%, respectively, in comparison to the control. Notably, the highest chlorophyll a content is observed in “Catharanthus roseus var. ocellatus” and “Catharanthus roseus var. roseus” under L-cys treatments (800 and 200 µM), respectively. Regarding Malondialdehyde (MDA) content, varieties of alba and. roseus “ exhibit higher levels than ocellatus variety. Notably, “Catharanthus roseus var. alba” treated with 800 µM L-cys showcases the highest optical density (0.59 OD g⁻¹ DW) and total alkaloid content for leaves. Furthermore, calculated correlations among phytochemical attributes reveal a significant positive relationship between total flavonoid content, total phenol content, and antioxidant activities in leaf and root organs. Elicitor responses underscore “Catharanthus roseus var. ocellatus” as the variety yielding the highest secondary compound production. Collectively, our findings underscore the suitability and efficacy of both melatonin and L-cysteine elicitors as valuable treatments to enhance secondary metabolite production in Madagascar periwinkle.