Relation between in vitro production of ascosonchine and virulence of strains of the potential mycoherbicide Ascochyta sonchi: a method for its quantification in complex samples

The potential of the Ascochyta sonchi fungus as a mycoherbicide for biol. control of the perennial weeds Sonchus arvensis and Cirsium arvense was studied. Ascosonchine, an enol tautomer of 4-pyridylpyruvic acid with potential herbicidal properties, is the main phytotexin produced by the fungus. A simple and sensitive method was developed for rapid quant. anal. of ascosonchine by HPLC with UV detection. The ascosonchine toxin contents in culture filtrates of 9 strains of A. sonchi were measured. The tested strains produced up to 2.7 mg ascosonchine/L when grown in static conditions for 4 wk. The toxin prodn. by each fungal strain was compared with the virulence on the host weed plant to det. if the most virulent strains could be selected by choosing the best toxin producers. The results did not support this assumption. The HPLC method was also used to quantify toxin prodn. under different fungal growth conditions to achieve the highest toxin prodn. The most productive fungal strain produced >8 mg/L when grown in static conditions for 8 wk.