Published online by Cambridge University Press: 01 April 2009
Introduction. Penicillium digitatum is a commercially important postharvest pathogen of citrus that is responsible for significant annual global losses. Strains of the fungus, which exhibit strong resistance to widely used synthetic fungicides, are of major concern to the industry. The aim of the study was to investigate the antifungal activities of polar extracts and compounds from Lippia species, indigenous to South Africa, against a Guazatine®-resistant strain of P. digitatum.Materials and methods. In vitro tests were done by incorporating the compounds and plant extracts into Malt Extract Agar at concentrations ranging from (0.2 to 1.0) mg·mL–1. An in vivo (curative) assay was conducted using the checkerboard technique on ‘Valencia’ oranges. Results and discussion. A strong correlation between the in vitro and in vivo results was observed. All the compounds and extracts were able to inhibit fungal growth at concentrations above 0.6 mg·mL–1. Verbascoside was the most active compound, while extracts of Lippia javanica and Lippia rehmannii caused significant inhibition of mycelial growth. The observed activity was largely ascribed to the presence of verbascoside in the plant extracts. Conclusion. Polar extracts of Lippia species have potential as environmentally friendly alternatives for the control of P. digitatum on citrus.