Phytopathogenic fungi and their resistance to conventional fungicides are increasingly becoming a problem and compromising the global supply of agricultural products. This is why researchers around the world are searching for effective alternatives. In Africa, all kinds of plant extracts have long since been used here, especially to combat phytopathogenic fungi and to modulate the rhizosphere.
The objective of this project was to extract fungicidal agents from African medicinal plants and test them in vitro and in planta using a suitable technology platform in order to develop products based on these extracts that could then be marketed in the future. The substantive focus here was placed in particular on plants that could be administered orally in human and veterinary medicine. This already implies low off-target toxicity in humans and animals, which is a key prerequisite if the approval procedure is to be a success.
Extracts were first gained from the barks, leaves and roots of various eastern African plants with the aid of different solvents from the eluotropic series before their toxicity was tested against the conidia and mycelia of relevant phytopathogenic fungi (e.g. Botrytis cinerea, Fusarium graminearum, Colletotrichum graminicola). Toxicity testing was conducted both in vitro (microdilution assay) and in planta (leaf infection assay, stem infection assay, fruit infection assay). The toxicity of the extracts was compared to that of conventional fungicides (e.g. tebuconazole). The results showed that plant extracts have an entirely comparable fungicidal effect. The plant extracts actually demonstrated a much better fungicidal effect in the case of fungicide-resistant, harmful fungi species (e.g. Fusarium graminearum, PH-1 strain). This is due to the fact that, over the course of evolution, several different fungicidal ingredients acting independently of each another were generally formed in plants as part of a co-evolutionary adaptation process to changing environmental conditions.
The plant extracts studied could be used, among other things, in seed dressing, as a fungicide in conventional crop protection and to treat the surface of citrus fruits. In addition to having a fungicidal effect, several plant extracts also demonstrated root growth induction in the case of wheat germ. Several plant extracts could therefore also be used as plant strengtheners.