Morpho-Physiological and Biochemical Responses of Plectranthus amboinicus to Varying Watering Regimes

Abstract

Water stress is a detrimental event that adversely impacts crop productivity on a global scale. A study was carried out to examine the impact of fluctuating water stress conditions on Jamaican thyme (Plectranthus amboinicus) plant morpho-physiological and biochemical indices. The treatments were regular watering (RW), drought (DR), flooding (FL), and resumption of regular watering after flooding (DHFL) or after drought (RHDR). The DR and FL treatments significantly (p<0.01) reduced plant fresh weight by 92% and 88%, respectively, compared to RW. The relative water content of DR plants showed a significant (p<0.01) reduction by 60% compared to the RW plants. Net photosynthetic rate, transpiration rate, and stomatal conductance were significantly (p<0.01) reduced in DR and FL plants; whereas sub-stomatal carbon dioxide was significantly (p<0.01) high in DR plants. Chlorophyll a, b, and carotenoids were significantly (p<0.05) reduced in the DR and FL plants compared to the RW plants. On the other hand, soluble sugar content in the DHFL plants was significantly (p<0.05) increased compared to that of the RW plants. FL plants showed a significant (p<0.05) increase in total 2,2-diphenyl-1-picrylhydrazyl scavenging effect by 156%, total flavonoids by 225%, total phenolics by 242%, and malondialdehyde by 94% compared to RW. In conclusion, this study highlighted the morpho-physiological and biochemical changes in Jamaican thyme plants under varied watering regimes. Jamaican thyme is an aroma medicinal plant and thus, further research should assess volatile organic compounds.