Unravelling the nature of soil suppressiveness to plant pathogens: A wide region analysis in the Verticillium wilt/Olive pathosystem

Trabajo presentado en el Rhizosphere 4: Stretching the interface of life, celebrado en Maastricht del 21 al 25 de junio de 2015.During the last two decades the phytosanitary status of olive crop in Spain is being severely threatened by Verticillium wilt (VW). Suppressive soils have been described worldwide for many different pathogens, however for the fungal pathogen Verticillium dahliae (VD) the information is very scarce. In this study a collection of rhizosphere soils from 93 olive orchards in a wide region of southern Spain, were characterized by their level of suppressiveness to VW. Results indicated that 25% of soils showed a high level of suppressiveness to VW. The objective of this study was to unravel the biotic and abiotic factors associated with this phenomenon. Using some “Classical” approaches we identified that soil texture (clay content) was highly associated to soil suppressiveness. Using ‘classical’ approaches we identified that microbial factors were also involved in this specific suppression including: 1) Transference of soil suppressiveness by adding small amounts of suppressive soil to conducive soil. 2) The treatment of suppressive soils with heat demonstrated reduction of suppressiveness. 3) Representative bacteria from suppressive soils show in vitro and in vivo biocontrol activity against VD. In a second step we used bar-coded pyrosequencing and characterized by abundance and identity, all bacterial communities associated to the rhizosphere of plants growing in 27 soils in the presence or not of the pathogen. NMDS, Classification and Regression Trees and PLS-DA analysis have allowed identifying some climatic parameters and physicochemical soil characteristics that are differentially associated to the level of suppressiveness of those soils as well as to determine which OTUs are specially enriched in the suppressive soils. Furthermore, specific OTUs have been identified as being transferred from the suppressive into the conducive soils which might be responsible of this ‘transferable’ suppressive effect.N