Soil suppressiveness towards Meloidogyne Verticillium or Pythium in greenhouse horticulture

Soils originating from fourteen greenhouse horticultural companies were assessed for the level of suppressiveness of three major pathogens of vegetables and flowers, namely the root knot nematode Meloidogyne incognita, Pythium aphanidermatum and Verticillium dahlia. As controls, three well-documented soils in terms of disease suppressiveness and coarse sand were included for each pathogen. Soils were distributed over three treatments with forty replicates each in a random block design under standardized conditions. Each soil was treated with ¿-radiation in order to assess the contribution of abiotic properties to disease suppressiveness. Non-sterilized soils served as a measure of abiotic- and biotic factors, and soil without the addition of pathogens served as a control to determine background contamination of indigenous pathogens. Soils were acclimatized for one week. Afterwards, irrigation was started and pathogens were inoculated. Survival stages of V. dahlia or P. aphanidermatum were added as pure suspensions, i.e., microsclerotia or oospores, respectively. For Meloidogyne, second stadium larvae (J2) were used. Seedlings were planted for M. incognita, while for P. aphanidermatum and V. dahlia, seeds were used. A large variation in the level of suppressiveness was observed. Soil suppressiveness towards Meloidogyne, Verticillium or Pythium was not correlated. This means that suppressiveness is pathogen dependent. However, soil structure contributes to a large extent to the level of suppressiveness as exemplified by the survival rate of Meloidogyne and Pythium in sandy soils. With this dataset we aim to unravel the underlying mechanisms and investigate whether suppressiveness levels can be increased and used in an integrated soil management system.