Saprobic fungi decrease plant toxicity caused by olive mill residues

We studied the influence of dry olive mill residue (DOR), as affected by saprobic fungi on the growth of soybean (Glycine max) and tomato (Lycopersicum esculentum). The application of 60 g kg(-1) of DOR decreased the dry weight of tomato and soybean plants mainly because of its phenolic content. The phytotoxicity of DOR decreased when it was incubated in the presence of almost all of the saprobic fungi tested. All saprobic fungi tested in our experiments were able to decrease the phenol content of DOR, and a correlation between the decrease in the phenol content of DOR by saprobic fungi and the increase in the dry weight of plants was found. However, the toxicity of these residues to either tomato or soybean plants did not decrease in the presence of all saprobic fungi in spite of a decrease in phenolic compounds. Some of the saprobic fungi tested eliminate completely the phytotoxicity of DOR. F. oxysporum 738 and F. lateritum were capable of transforming the DOR, after incubation for 20 weeks, so that the tomato plants to which this transformed DOR was applied increased significantly in shoot dry weight compared with the tomato plants which did not receive DOR. These results open the possibility of the use of DOR as organic fertilizer. (C) 2003 Elsevier B.V. All rights reserved.