Estimation of secondary metabolites of indigenous medicinal plant extracts and their in vitro and in vivo efficacy against tomato early blight disease in Pakistan

Abstract

Fifteen Pakistan’s indigenous medicinal plant extracts were investigated for various secondary metabolites and their potential against tomato early blight disease. In vitro screening of aqueous and methanolic extracts of fresh and dry plant parts was performed against Alternaria solani at 20, 40, 60 and 80% concentrations, by mycelial inhibition measurement through food poison technique. The aqueous extracts of Azadirachta indica, Allium sativum and Ocimum sanctum showed significant antifungal activity at all tested concentrations. Aqueous extract of fresh plant material was found more effective than that of dry plant material and the methanolic extracts of fresh or dry plants. Phytochemical analysis of extracts revealed that the antifungal potential was directly related to the type and quantity of secondary metabolites. The highest phenolics were recorded from A. indica (56.43 mg gallic acid equivalent (GAE)/g) followed by A. sativum (54.25 mg GAE/g) and O. sanctum (53.38 mg GAE/g), respectively. The aqueous extracts of fresh A. indica, A. sativum and O. sanctum were also found effective when applied to plants grown in greenhouse and field. A. indica extracts reduced disease incidence to 62.32%, in the greenhouse increasing the yield up to 138 g/plant over control (94.33 g/plant), while in the field experiment A. sativum showed highest reduction in disease incidence to 77.42% with an increasing yield up to 3.70 t/ha compared to control (2.43 t/ha). The results of this study indicate that aqueous extracts of fresh A. indica, A. sativum and O. sanctum have great potential to be used to control early blight disease of tomato in the field.