Synergistic Activity of Leaves Extracts of Mansoa alliacea L. and Allamanda cathartica L. to Inhibit Athelia rolfsii, the Cause of Stem Rot Disease in Peanut Plants

Abstract Stem rot disease in peanut plants caused by Athelia rolfsii is an important disease because it can reduce peanut yield up to 13-59%. The study aimed to evaluate the synergistic activity of the leaves extracts of Mansoa alliacea L. and Allamanda cathartica as an alternative control of stem rot disease in peanut plants. Testing of Antifungal activity was carried out in the laboratory included: diameter of inhibition zone test with diffusion well method; colony growth test, sclerotia germination test, fungal biomass test, and ultrastructure observation using scanning electron microscope (SEM). The results showed that the crude extracts of the leaves of M. alliacea and A. cathartica were able synergistically to inhibit the growth of the fungus A. rolfsii with diameter of inhibition by 42 mm, while the diameter of inhibition zones for leaf extract of M. alliacea L. was only 30 mm and as for A. cathartica L. was only 9 mm. Minimum inhibitory concentration (MIC) of the mixture of leaves extracts of Mansoa alliacea L. and A. cathartica L. was 0.8% (w/v). Treatment with the extract’s mixture significantly (P?0,05) inhibited colony growth, germination rate of sclerotia, and fungal biomass of A. rolfsii. The result of mycelial observation of A. rolfsii by using SEM showed that surface of fungal mycelia treated with extract looked smaller in size and shrunk, and leakage of cell wall became visible; while at the control, the surface of mycelia remained intact and thrived perfectly. Keywords: synergistic activity, leaves extract, stem rot disease