The effect of biostimulants and light wavelengths on the physiology of Cleome gynandra seeds

Abstract

Cleome gynandra L. is used as a vegetable that forms a significant part of the local diet in South Africa and other tropical and subtropical parts of the world. Cleome gynandra seeds are negatively photoblastic (light-induced dormancy) and fail to germinate when planted immediately after harvest. To enhance better cultivation practices, seed germination of C. gynandra using different light wavelengths (red, far-red, green and blue light) with and without organic biostimulants [smoke–water (SW), karrikinolide (KAR1), Kelpak® (KEL) and eckol (ECK)] was tested. Among all the tested biostimulants, the best germination percentage (40%) was observed in seeds treated with SW in the dark. However, the biostimulants did not show any significant effect with the light treatments. In this study, blue light generally promoted (≤ 35%) and red light inhibited (≤ 8%) germination. Furthermore, the effect of different biostimulants (under blue and red light) on biochemical content and enzyme activities was tested in seeds of C. gynandra. Seeds treated with biostimulants in blue light showed an overall increase in protein and total carbohydrate content in comparison to seeds subjected to biostimulants in red light. The α-amylase activity in the seeds was highest in KEL-treated seeds in blue light. Superoxide dismutase and catalase activity was generally higher in blue-light treatment, while peroxidase activity was highest in red light. Enhanced germination under blue light and inhibitory effects with red light is an intriguing phenomenon for C. gynandra seeds, which needs more detailed investigation. The study also indicates the potential application of organic biostimulants (particularly SW) for better seed germination and growth of C. gynandra which can be explored by farmers in the field.