Activity of ethanolic extracts of spices grown in Tanzania against important fungal pathogens and early blight of tomato

Geraldin M. W. Lengai, Ernest R. Mbega and James W. Muthomi

Abstract: The nutritional and economic value of tomato is universally recognized yet its production in many regions is still low due to, among other reasons, fungal diseases. Farmers have desperately relied on synthetic chemical pesticides to manage the diseases but the chemicals, in spite of their efficacy, are associated with residual detrimental effects on human health and environment. The objective of this study was to evaluate the antifungal activity of selected spices against important fungal pathogens of tomato. Bioactive compounds from seven spices namely clove, black pepper, turmeric, ginger, lemongrass, cinnamon and cardamom powders were extracted in ethanol and tested for antifungal activity against Alternaria solani, Fusarium oxysporum f. sp lycopersici and Pythium sp. in poisoned food bioassay. The most active spice extracts were further tested for efficacy against early blight of tomato under field conditions. All extracts were significantly active against the tested fungal pathogens by about 85%. Clove extract was the most active against all the pathogens inhibiting their growth 100%. Ginger, black pepper and turmeric extracts inhibited growth of all the pathogens by between 74-80%. Lemongrass extract was the least active with an antifungal activity of about 49%. Under field conditions, clove remained active in reducing early blight disease load by about 36% compared to the negative control. The antifungal activity demonstrated by the spice extracts is an indication that they could be relied upon for disease control and this study recommends their consideration, especially clove, for formulation into a botanical fungicide for management of early blight of tomato.

Keywords: Alternaria solani; Botanical fungicide; Fusarium oxysporum f.sp. lycopersici; Pythium; Solanum lycopersicum

Date published: 2021-12-15