Biological control of Chenopodium album L. in europe

Ascochyta caulina (P. Karst) v.d. Aa and v. Kest is a plant pathogenic fung us which is specific to Chenopodium album L. It has been suggested as a pot ential mycoherbicide to this weed, which is important and wide spread in ar able crops throughout Europe. To investigate its potential as a biocontrol agent, the fungus has been tested in glasshouse and field experiments. Form ulations containing different combinations of A. caulina conidia, the phyto toxins from the fungus and low doses of herbicides have been tested. Signif icant improvement in the efficacy of the fungus was achieved in glasshouse trials with an aqueous formulation containing PVA (0.1% v/v), Psyllium (0.4 % w/v), Sylgard 309 (0.1% v/v), nutrients and conidia (5 x 10(6)/ml). The e xtracellular, hydrophilic phytotoxins produced by A. caulina were purified and their structures determined. The main toxin, named ascaulitoxin, was ch aracterised as the N-2-beta -D-glucopyranoside of the unusual bis-aminoacid 2,4,7-triamino-5-hydroxyoctandioic acid. Two other toxins proved to be tra ns-4-amino-D-proline and the aglycone of ascaulitoxin. These toxins have sh own promising herbicidal properties. Field trials have investigated the per formance of A. caulina conidia applied at different developmental stages of C. album either as a single treatment or combined with sub-lethal doses of herbicides or with the fungal phytotoxins. With the available formulation, favourable weather conditions are needed to obtain infection in the field. The efficacy of the strain of A. caulina used so far has proved to be inad equate to justify its development as a bioherbicide. This is probably due t o its low virulence.