Ecotoxicological characterisation of a mycoherbicide mixture isolated from the fungus Ascochyta caulina.

Background: Recent studies have highlighted the possibility of using a mixture of three fungal toxins produced by Ascochyta caulina as a bioherbicide to control noxious weeds. However, to assess the commercial potential of this new bioherbicide, it is necessary to increase knowledge regarding the environmental behaviour of these toxins, and particularly their effects on non-target organisms. A negative ecotoxicological profile of this potential bioherbicide could eventually hinder its registration.

Results: In this study, acute and chronic effects of the A. caulina toxins (ACTs) on non-target organisms were evaluated in the laboratory. The (96 h) calculated algal Er C50 and NOEC were 142.7 and <12.5 mg L(-1) respectively. For daphnids, the EC50 (48 h, acute test) was 20.1 mg L(-1) , whereas the NOEC (21 day chronic reproduction test) was 6.3 µg L(-1) . No cases of mortality, sublethal effects or abnormalities were observed in the acute and chronic tests for Brachydanio rerio at a concentration of 100 mg L(-1) , indicating a low toxicity of ACTs for this organism. The calculated LC50 (14 days, acute test) and NOEC (56 day chronic reproduction) for earthworms were >1000 and ≥250 mg kg(-1) soil respectively.

Conclusions: The present study has provided baseline information needed to assess the potential hazard of the fungal toxins of A. caulina. In particular, the acute and chronic effects on aquatic (algae, Daphnia and fish) and terrestrial organisms (earthworms) have been highlighted. Finally, a comparison of the inherent toxicity of ACTs with other synthetic herbicides has shown comparative ecotoxicity of the tested mixture.