Biofumigation for the control of soilborne diseases

Soilborne pathogens may cause severe reductions in yield and/or damage yield quality, resulting in serious economic losses. Pathogens such as Fusarium oxysporum, Rhizoctonia solani, Verticillium dahliae and Pythium spp. affect various crops (tomato, cucumber and pepper, among others) grown under organic management in greenhouses. These pathogens are difficult to control because of their persistence in the soil and wide host range. Biofumigation refers to the suppression of soilborne pathogens and pests by volatile biocidal compounds (mainly isothiocyanates) released from decomposing Brassica tissues incorporated into the soil when used as green manure crops. We developed a bioassay, in which only the volatile compounds effects are tested, as an efficient tool for the rapid screening of plants for biofumigation, and for the optimization of different aspects of the process (such as green manure concentration and most effective plant organs). The fungicidal effect of cruciferous crops against R. solani was demonstrated in pot and greenhouse experiments: yields were increased and disease was suppressed. The effect of solarization alone on controlling root-knot nematodes was clearly observed, and the combination of solarization with green manure residues or compost resulted in even better disease suppression. In summary, biofumigation can be considered a useful addition to the integrated pest management (IPM) arsenal for the reduction of soilborne pathogens, especially in organic management, where it may be the most promising solution.