Fungal phytotoxins for control of Cirsium arvense and Sonchus arvensis

Perennial weeds, including Cirsium arvense and Sonchus arvensis, are a common problem in crop fields, especially in agricultural systems with reduced herbicide usage. Herbicides recommended for control of these perennials generally are restricted to only a few active ingredients that tend to have low selectivity, especially on dicot crops. Microbial phytotoxins or their synthetic analogues may be candidates for new weed-control options. Many plant pathogens, especially necrotrophic or hemibiotrophic fungi, produce a range of phytotoxins responsible for disease damage and may be a source of such useful metabolites. Several pathogens, including Stagonospora cirsii and Ascochyta sonchi, were found commonly on C. arvense and S. arvensis, and these fungi also produce phytotoxic metabolites. Phyllosticta cirsii and Phomopsis cirsii, belonging to two well-known toxin-producing genera, have also been proposed for biocontrol of C. arvense. Phytotoxins isolated from these fungal pathogens are metabolites belonging to several classes of natural compounds including enol pyruvic acid derivatives, cytochalasins, nonenolides, oxazatricycloalkenones, pentasubstituted bicyclooctatrienyl ester of acetic acid, pentasubstituted hexahydrobenzodioxine carboxylic acid methyl ester, and β-nitropropionic acid. Some of these metabolites may be used as biomarkers, for studies on mode of action and development of structure-activity relationships.