Elucidation of antioxidant fractions in leaves of Dendrophthoe falcata L. and standardisation of tape method of control

Abstract

Dendrophthoe falcata is a partial stem parasite belonging to Loranthaceae family, which is considered as a destructive pest of many economically important fruit trees such as mango, sapota, sugar apple and guava. They cause damage to the host plants by depleting nutrients, releasing toxins, and limiting their growth. Though several management strategies have been suggested by previous researchers which include pruning of its branches, base banding using 2,4-D and spray of ethrel in combination with organosilicone (non-ionic surfactant), the latter gave a promising response in comparison to others without affecting the host. Because of its destructive nature, some of the potential pharmaceutical features of the parasite often go unnoticed; if prospectively exploited it will automatically open up avenues for targeted removal of the parasitizing aerial parts of D. falcata. Plants are thought to be one of the most important sources for discovering and developing pharmaceuticals that are both effective and safe compared to currently available synthetic drugs. Traditional and folk medicines are gaining favour over contemporary therapy due to fewer side effects and a higher safety margin. Dendrophthoe falcata, a widely distributed plant in India, is one of nature's many plants with medicinal characteristics. The potential medicinal property of Loranthus has been reported in Ayurveda. It is reported to have diuretic, wound healing, anti-microbial, anti-helminthic, anti-fertility, antioxidant, anti-cancer, anti-diabetic, anti- hyperlipidemic and anti-hypersensitive activities. Medicinal properties of mistletoes are host specific. The antioxidant property of these parasitic plants might be due to their phenolic compounds including tannins and flavonoids. However, it will be very interesting to identify the novel antioxidant principles in the context of specific host associations. The present study was envisaged with a major aim of characterisation and elucidation of bioactive antioxidants from D. falcata leaves by invitro assays and identification of bioactive compounds through GC-MS/MS with prospective pharmaceutical applications, and standardization of efficient and non-regenerative method to control Loranthus.The experiments were carried out in Department of Plant Physiology, College of Agriculture, Vellanikkara, Thrissur. In the first experiment the leaf samples of Dendrophthoe falcata inhabiting different hosts namely mango, jackfruit, cocoa and sapota were collected, powdered and extracted in various organic solvents such as chloroform, petroleum ether, ethyl acetate, methanol and water followed by computation of extract yields. Aqueous extracts of D. falcata inhabiting all the hosts showed significantly higher (10.2 to 14.8%) yields compared to other solvents. Extract yield in case of petroleum ether and ethyl acetate were reported to be lowest (1.6 to 2.9% respectively) compared to other solvents indicating polar inorganic extraction to be advantageous, although novel and unique bioactive compounds could be effectively extracted in the latter. D(Sapota) showed lowest extract yield in petroleum ether (1.6%) and ethyl acetate (1.7%), whereas D(Jack) and D(Cocoa) had higher extract yields of 14.8% and 14.4% in water respectively. Free radical inhibition activity of D. falcata were assessed using DPPH radical scavenging assay in different hosts across various solvent extractions at different time intervals. Chloroform and water extracts of D. falcata showed an increasing trend in inhibition activity with time. However, ethyl acetate extracts marked a reduction in inhibition activity after two hours of incubation. Qualitative phytochemical screening of different extracts of D. falcata on the four hosts namely mango, jackfruit, cocoa and sapota were carried out to detect the presence of alkaloids, phenols, saponins, flavonoids, terpenes, tannins and steroids. There was a differential display of possession of different classes of phytochemicals by D. falcata across different host associations which varied with the nature of solvent used for extracting the antioxidant fractions. Chloroform extract of all the four hosts infested with D. falcata contained alkaloids, phenols, flavonoids, terpenes and steroids. Ethyl acetate extract had comparatively lesser phytochemicals, whereas methanolic extract had alkaloids, saponins, phenols, flavonoids, terpenes and steroids. Water extract yielded tannins along with other phytochemicals. Based on the antioxidant potential of the different extracts and host specificities, eight samples were shortlisted for GC- MS/MS analysis. Bioactive substances were detected in different extracts of D. falcata during GC-MS/MS analysis. Two common and abundant bioactive principles viz. cis- vaccenic acid and n-hexadecanoic acid were extracted in higher abundance in the petroleum ether extracts of D(sapota) and D(jack) for the former and D(jack) for thelatter. Petroleum ether extraction resulted in the best profiling for both the bioactive compounds from D(jack), indicating the association of D. falcata with jack as the most potential one to be tapped for pharmacological uses. The second experiment was carried out at Cocoa farm of Cocoa Research Centre, Kerala Agricultural University, Thrissur where the cocoa trees infested with Loranthus were tested for efficient management by impregnating the super absorbent polymer, super absorbent cotton and super absorbent paper with a combination of Ethrel and surfactants like oraganosilicone (OS)/alcohol ethoxylate (AE) @ 25mL/L of Ethrel + 0.5 mL/ L OS/AE and developed as a tape. Fresh and 1 week dried tapes were comparatively assessed, of which fresh application performed better than dried. The rate of defoliation also increased with time and after a while the number of leaves defoliated remained constant. Among the applicant material used, super absorbent polymer was found to be superior to super absorbent cotton and paper. Percent defoliation due to both surfactants revealed that AE performed better than OS. Ethrel along with surfactant alcohol ethoxylate (AE) as a sticky tape using superabsorbent polymer as the impregnating material can be used as an effective management strategy as AE is more eco-friendly than organosilicone. The tape method can also be an alternative to spraying even in the event its longer time for defoliation, provided if it ensures similar regrowth restriction efficiencies.