Optimization of the production of the herbicidal toxins by the fungus Ascochyta caulina

Safer and more environmentally friendly methods, including the use of natural substances, would be favorably considered for weed management, particularly in those habitats where the use of chemicals is restricted or banned. Ascochyta caulina, a proposed mycoherbicide for biocontrol of the weed Chenopodiumalbum, produces in liquid culture three main metabolites proposed as possible natural herbicides. Recently a research project,namedECO-VIA, initiated a series of studies aimed at developing the technologies to obtain a natural herbicide based on these bioactive metabolites. Particular attention was given to: maximizing toxin production; lowering the production costs; scaling up the production in fermentation systems; setting up a large scale purification method and identifying fast and inexpensive chemical methods to quantify toxins yields. The fungus proved to grow well and to produce up to 230 mgof toxins l_1 culture when grown for 5-10 days in shaken conditions, provided the initial inoculum was at least 105-106 conidia ml_1 of culture. Toxin production was improved by the addition of yeast extract to the medium. Given suitable inoculum and growth conditions, a stirred fermenter could be suitable for mass production of toxin.