In vitro antioxidant and antifungal activities of different solvent extracts of leaf peel and gel of Aloe succotrina and their bio-control of leaf spot disease of Phaseolus vulgaris seedlings

Abstract

Phytochemical constituents, in vitro antioxidant and antifungal activities of leaf peel and gel of Aloe succotrina (Xanthorrhoeaceae) using different solvents, n-butanol, ethylacetate, water and methanol, were evaluated. The antifungal effects of these different solvent extracts against pathogenic fungi, Alternaria alternata, Cladosporium cladosporioides and Cochliobolus specifer, causing leaf spot disease of seedlings of Phaseolus vulgaris were evaluated. In addition, their effects on different growth attributes and metabolite content of treated P. vulgaris seedlings were measured. Highest flavonoid content was measured in the ethylacetate extract, while, the highest concentrations of saponins and tannins were measured in butanol extract. Water and methanol exhibited higher phenolic content. All solvent extracts of leaf peel and gel of A. succotrina could be categorized as strong radical scavengers based on their respective inhibitory concentration at 50% scavenging activity (IC50) values. The highest total antioxidant capacity (TAC) was measured for the methanol leaf peel extract [194.04 mg ascorbic acid (AA) equivalent /g dry weight (DW)]. Alternaria alternata was the most resistant species showing the least growth inhibition percentages in vitro antifungal assays. All plant extracts exhibited considerable growth inhibition (> 70%) with C. cladosporioides referring to its pronounced susceptibility. The leaf spot disease incidence of P. vulgaris seedlings was completely disappeared after seedlings treatment by the methanol leaf peel extract of A. succotrina. Moreover, most measured seedlings growth attributes, e.g., the shoots and roots lengths, the contents of photosynthetic pigments and carbohydrates were significantly enhanced. The methanol extracts of leaf peel of A. succotrina could be considered as potential sources of antioxidant as well as antifungal compounds to control A. alternata leaf spot disease. Treatment of P. vulgaris with water leaf and gel extracts of A. succotrina improved its growth attributes and resistance against leaf spot caused by Cladosporium cladosporioides and Cochliobolus specifer.