Abstract:
The fungus Rhizoctonia solani Kuhn (R. solani) is the causative agent of the infection of sheath blight disease, which has harmful effects on rice (Oryzae sativa) cultivation in Sri Lanka. The approach to combating the disease by applying fungicide is expensive and builds a hazardous environment for humankind, fauna and flora. The present study aimed to assess the in vitro antifungal activity of extracts of Calatropis gigantea (L.) W.T.Aiton (giant milkweed), Antigonon leptopus Hook. and Arn. (coral vine), and Parthenium hysterophorus L. leaves and flowers against R. solani to control the sheath blight disease in rice cultivation. To substantiate the antifungal properties, various chemical tests were performed on the dry powder of the leaves and flowers to detect certain phytochemicals,
including glycosides, tannins, saponins, proteins, flavonoids, terpenoids, and phenol. The extraction process was done by using different solvents, such as hexane, acetone and distilled water. Stock solutions were prepared by adding 10 ml of the solvent to the crude extracts. The antifungal assay and finding the Minimum Inhibition Concentration (MIC) value were performed using the poisoned food technique and IC 50 and IC 90 values were calculated by probit analysis. Data were analyzed using IBM SPSS Statistics (one way ANOVA and DMRT test) at 0.05 significant level. The majority of tested phytochemicals were found in the leaves and flowers. Compared to the hexane extracts of the studied weed species, acetone and distilled water extracts demonstrated antifungal activity against R. solani and the acetone extract of the flowers of A. leptopus exhibited the strongest
antifungal properties. The acetone extract of A. leptopus flowers had the MIC value of 4.85 mg/ml, and IC 50 and IC 90 values were 1.74 mg/ml and 4.66 mg/ml, respectively. More than 60 % of growth inhibition was reported by the distilled water extract of the leaves of A. leptopus and P. hysterophorus and these extracts can be applied as a homemade fungicide. The acetone extract of the flowers of A. leptopus is an appropriate agent to scrutinize the potential of formulating a novel bio fungicide to manage sheath blight disease in rice cultivation
