Botanical fungicides: natural and semi-synthetic ceveratrum alkaloids

Abstract

The practical potential of the main bioactive principles of sabadilla, a botanical insecticide prepared from the seeds of Schoenocaulon officinale, and related semi-synthetic ceveratrum alkaloids in controlling phytopathogenic bacteria and fungi was explored. Evaluating 35 compounds belonging to this group of steroid alkaloids revealed antimicrobial effects against Erwinia, Corynebacterium, Fusarium, Glomerella and Plasmopara species. Significant activities were displayed against the sunflower downy mildew fungus, Plasmopara halstedii. The ceveratrum alkaloids are thought to interact with the cell membrane, disrupting its integrity and/or altering its function. In contrast to commercial fungicides affecting either the parasitising thallus or the asexual spores of P. halstedii, ie, only a single developmental stage, the alkaloids tested disrupt its life cycle at several points in host-dependent and host-independent stages. Among the natural alkaloids, cevacine and cevadine were the most effective against sunflower downy mildew and the activity of the semi-synthetic oleoyl veracevine and cevagenine was comparable to that of metalaxyl. Sunflowers showed good tolerance to these highly active natural and semi-synthetic ceveratrum alkaloids. Our results indicate that the modest anti-oomycete activity of the natural sabadilla components can be greatly improved by appropriate structural modifications and thus establish the ceveratrum alkaloids as potential antifungal agents with a novel mode of action. © 1999 Society of Chemical Industry