Sustainable use of thirteen South African medicinal plants for the management of crop diseases caused by Fusarium species – An in vitro study

Abstract

Crop fungal infections such as those caused by Fusarium species often result in yield loss pre- and post-harvest and during storage, contaminate food and exacerbate food insecurity. Synthetic fungicides are becoming less attractive as they pose health risks to consumers and are not environmentally friendly. As an alternative to synthetic fungicides, medicinal plant species may present sustainable and affordable sources of environmentally friendly fungicides for controlling plant diseases. This study was aimed at evaluating the in vitro antifungal activity of different medicinal plant extracts individually or in combination against Fusarium proliferatum, F. solani, F. verticillioides and F. graminearum. Different solvent (water, acetone and ethyl acetate) extracts obtained from the leaves of thirteen medicinal plant species were evaluated for antifungal activity using the micro-plate dilution assay. Their combined effect was evaluated by determining their fractional inhibitory concentration index (FICI). When evaluated individually, acetone extracts obtained from Combretum erythrophyllum, Harpephyllum caffrum and Quercus acutissima were the most active extracts inhibiting the growth of all the four pathogens with minimum inhibitory concentration (MIC) values less than 0.1 mg/ml. Out of 204 extract combinations evaluated, 150 extract combinations demonstrated either synergistic or additive antifungal activity. among the best combinations, combined acetone extracts of Harpephyllum caffrum and Combretum erythrophyllum showed strong synergistic antifungal activity against F. graminearum, F. proliferatum and F. verticillioides (MIC values of 0.02 mg/ml, 0.002 mg/ml and 0.001 mg/ml, respectively), and strong additive antifungal activity against F. solani (MIC = 0.02 mg/ml). The approach of using medicinal plant extracts from renewable plant parts either individually or in combination is sustainable, affordable, environmentally friendly and may be more beneficial in the fight against crop pathogenic diseases, particularly in organic farming.