Antifungal Activity of Phyllanthus Amarus, Passiflora Foetida and Costus Afer Against Colletotrichum Species Causing Leaf Blight on Citrullus Lanatus (egusi Melon)

Citrullus lanatus (Thumb Mansf.) (Egusi melon) is an important vegetable in West Africa grown for its edible seeds and oil. Its productivity is limited by leaf blight disease (LBD) which is dangerous to humans and the environment to control with synthetic fungicides. This study investigated the antifungal activity of some botanicals on Colletotrichum truncatum and Colletotrichum gloeosporioides causing LBD of Egusi melon. Four concentrations (5.0, 7.5, 10.0 and 12.5%) of aqueous extracts of Phyllanthus amarus leaves (PaL), Passiflora foetida leaves (PfL), Costus afer leaves (CaL), -stems (CaS) and -rhizomes (CaR) were evaluated against the pathogens in vitro, using agar poisoning. These extracts, except CaS (at 5, 10 and 50% w/v/50 seeds), were also evaluated for seed treatment under screen-house conditions. Data were collected on colony diameter reduction, sporulation, disease incidence, severity, seed germination, vine length, number of leaves and number of vines. Fungitoxicity of the botanicals varied with plant parts and extract concentrations. Phyllanthus amarus (7.5–10%), PfL (12.5%) and CaR (5–10%) significantly (p˂0.05) reduced C. truncatum mycelia growth (by 8.5–44.5%) and sporulation (by 22.3–90.9%), whereas 5–10% of PaL, PfL, CaR and CaL reduced growth (14.3–33.3%) and sporulation (9.6–96.4%) of C. gloeosporioides. Fungitoxicity was lowest in CaS. The botanicals, when used in seed treatment, significantly reduced disease incidence and severity, increased vine length and number of leaves without any effect on seed germination, while PfL, PaL and CaR (at 5, 10 and 50% w/v/50 seeds) were as effective as the synthetic fungicide (Mancozeb). High contents (mg/100 g) of alkaloids, flavonoids, saponins, tannins, glycosides, steroids and phenols detected from the botanicals might have enhanced their antifungal property. The high fungicidal potentials of P. amarus, P. foetida and C. afer (leaf and rhizome) on leaf blight of Egusi melon can be harnessed as safe biopesticides towards a better crop protection.