In vitro and field evaluation of selected spices as botanical fungicide for management of Phytophthora infestans, causative agent for late blight in tomato

Late blight of tomato, caused by Phytophthora infestans, is responsible for massive losses in yield of open field-grown tomato and is managed by use of synthetic fungicides. The rising demand for food safety calls for alternative yet effective crop protection products. Using a bioassay-guided approach the antifungal properties of ethanolic extracts of seven spices was evaluated and the constituents of the most inhibitory fraction determined using coupled gas chromatography-mass spectrometry. Clove extract was the most active and inhibited (100%) growth of P. infestans followed by black pepper (91%) turmeric (87%) and ginger (85%). The hexane fraction of clove extract equally inhibited growth of P. infestans 100%. The spice extracts reduced severity of late blight by between 29% and 40% with black pepper being the most efficacious under field conditions. These findings show the fungicidal potential of selected spices for the management of late blight of tomato.