Phytochemical and antifungal screening of Monoon longifolium leaf acetone extract

Abstract

Prolonged and indiscriminate use of fungicides in agriculture can have adverse effects on human health and the environment while also causing pathogen population shifts rendering their efficacy. Hence, the development of eco-friendly alternatives has become a necessity. Monoon longifolium is a widely distributed plant in Sri Lanka, known for its pharmaceutical and antimicrobial properties. Thus, this study aimed to investigate the phytochemical composition and antifungal activity of M. longifolium leaf acetone extract against three fungal pathogens of Solanum melongena (brinjal). Phytochemicals in cleaned, dried leaves of M. longifolium were extracted into acetone, and their total phenolic (TPC) and flavonoid (TFC) content, and antioxidant activity by DPPH radical scavenging were determined. Preparative thin layer chromatography (TLC) was performed with ethyl acetate: methanol: water (5:1:5) solvent system, followed by individual biochemical testing for each band. GC-MS analysis were performed to assess the phytochemical diversity in the M. longifolium crude extract, while the antifungal potential of these compounds was determined with WAY2DRUG PASS online server. Antifungal activity of the crude extract at 2000 and 3000 ppm concentrations was evaluated against three pathogenic fungi of S. melongena i.e. Diaporthe eugeniae, Pseudopestalotiopsis theae, and Lasiodiplodia theobromae by poisoned plate method by calculating the growth inhibition percentage. Captan, sterile distilled water and DMSO were used as positive, negative and experimental controls respectively. All antifungal screening tests were triplicated and analyzed by Kruskal-Wallis nonparametric and Dunn-Bonferroni post-hoc tests (p = 0.05). TPC and TFC of the crude extract were 23.16 ± 1.67 mg GAE /g and 137.6 ± 7 mg QE/g, respectively. DPPH radical scavenging activity of the extract had an IC50 of 0.135 mg/mL, while IC50 for the ascorbic acid standard was 0.251 mg/mL. TLC resulted in seven bands (Rf values 0.11, 0.25, 0.40. 0.49. 0.59, 0.69 and 0.89) and biochemical tests indicated the presence of seven phytochemical groups, i.e. alkaloids, flavonoids, tannins, phenols, saponins, terpenoids and polyphenols. Phenols and saponins were present only in the bands with Rf value of 0.89 and 0.11 respectively. The other five bands contained multiple phytochemical groups. GC-MS analysis identified 19 prominent volatile compounds with peak areas higher than 1%, of which β-caryophyllene oxide indicated the highest antifungal potential (PA = 0.647) according to PASS analysis. The highest antifungal activity at 3000 ppm was against P. theae (82.66 ± 1.5%) though not significantly different from L. theobromae (78.88 ± 0%, p > 0.05). The lowest activity was against D. eugeniae (63.77 ± 0.5%) at 2000 ppm while no difference was observed between 2000 and 3000 ppm concentrations against any fungal pathogen. The outcome of this study signifies the potential to use M. longifolium leaf extracts in control of fungal phytopathogens, warranted through field experiments.