Soil suppressiveness to soilborne pathogens can evolve following the incorporation of plant residues in the soil and solarization. We studied its occurrence by assessing disease incidence and severity in sandy soil which was infested after the disinfestation treatment. Disease incidence and severity of crown and root rot in cucumber plants inoculated with Fusarium oxysporum f. sp. radicis-cucumerinum macroconidia were reduced by 20 to 80% when seedlings were planted in the tested soils 2 to 34 months after soil amendment. Residues of Diplotaxis tenuifolia (wild rocket [WR]), Artemisia dracunculus (tarragon), Salvia officinalis (sage), and Brassica oleracea var. italica (broccoli) were most effective for inducing soil suppressiveness. Effective soil suppressiveness continued to be evident after repeated inoculations and plantings in the same soil without additional treatment between inoculations. Moreover, residues of WR induced soil suppressiveness in two additional tested soils differing in their physical and chemical properties. Residues of Rosmarinus officinalis (rosemary), Coriandrum sativum (coriander), Mentha piperita (peppermint), and B. oleraceae var. botrytis (cauliflower) induced disease suppression at the first inoculated planting but not upon repeated inoculation and planting. The contribution of soil solarization to the evolution of soil suppressiveness, albeit evident, was inconsistent. Soil suppressiveness to Fusarium crown and root rot was also observed when cucumber seed were sown in soils which were initially amended with WR residues and later infested with F. oxysporum f. sp. radicis-cucumerinum chlamydospores. There is a potential for the use of plant residues for inducing soil suppressiveness and further contributing to the control of diseases caused by soilborne pathogens.
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