A Thesis Submitted in Fulfilment of the Requirements for the Degree of Doctor of
Philosophy in Life Sciences of the Nelson Mandela African Institution of Science and
Technology
Tomato (Solanum lycopersicum L.) is affected by many fungal diseases and farmers rely on
synthetic pesticides for management. Detrimental effects associated with injudicious use of
chemical pesticides have caused a demand for alternative crop protection products. The
objective of this study was to evaluate the antifungal activity of selected spices against major
fungal pathogens and blight diseases of tomato. An ethnobotanical survey for ginger and
turmeric and evaluation of awareness of botanical pesticides use and collection of commonly
consumed spices was conducted in Tanzania. Ethanolic extracts from spices were prepared by
maceration and tested for antifungal activity in posisoned food bioassay against Phytophthora
infestans, Alternaria solani, Fusarium oxysporum f.sp. lycopersici and Pythium spp in vitro,
their effect on seed germination and efficacy on severity of early and late blight diseases of
tomato in. The most active extracts were fractionated in solvents with varied polarity, analyzed
for biochemical composition and tested for fungicidal activity. Results indicated that among
the tested spices, clove extract was the most active, inhibiting all the fungal pathogens (100%).
Combined effect of the most active extracts showed that clove combined with either ginger,
black pepper or turmeric inhibited growth of P. infestans (100%). The activity of solvent
fractions was lower compared to the crude ethanolic extracts, except for clove fractioned in n hexane which completely inhibited the growth of P. infestans. Therefore, the most active
compounds were better extracted in ethanol. Gas chromatography- mass spectrometry analysis
of the clove’s n- hexane fraction showed high abundance of eugenol (74%) which is likely to
be responsible for the high antifungal activity. High concentrations of the spice extracts
deterred and slowed germination but low concentrations stimulated seed germination of up to
98%. Under field conditions black pepper extract reduced severity of late blight by 40% while
clove extract reduced severity of early blight by 35% compared to the untreated control. The
findings herein are proof of activity of spice extracts under in vitro and field conditions. This
study recommends that the most active extracts be considered for development of a broad
botanical fungicide for management of fungal diseases of tomato.