A multiple approach towards soil-borne disease biocontrol

The difficulty encountered in controlling soil-borne diseases, even by chemicals, is probably due to the complicated ecosystem of the soil, where a number of interactions occur. The adoption of correct agronomic practices normally prevents damages, but in the presence of favourable conditions diseases spread rapidly almost without any possibility of control, apart from methods with high environmental impact, like soil fumigations. Milder alternatives are represented by biological methods but the awareness of their moderate effectiveness suggests combining some of them in a multiple integrated approach. In this view, methods aimed at lowering pathogen inoculum in the soil could be envisaged at different levels: (i) directly, by green manure of biocidal crops, like Brassicaceae, which exert a natural fumigating effect by releasing fungitoxic compounds; (ii) indirectly, by treating Brassicaceae seeds with a selected biological control agent like Trichoderma, for facilitating the establishment of the antagonist, so as to enhance soil suppressiveness, and provide a source of inoculum for the subsequent crop; (iii) indirectly, on the crop, by treating seeds with Trichoderma strains selected for rhizosphere competence and antagonistic effectiveness towards the pathogens. Data are reported from preliminary experiments carried out in greenhouse and field, towards soil-borne pathogens of sugar beet according to the above mentioned approaches.