## 2 Soil-Borne Plant Pathogens and Microbiota Determine Disease Suppression
The suppression of _G. graminis_ var. _tritici_[75], which is responsible for the take-all decline of wheat, is one of the most cited examples of induced specific suppression by a monoculture system [22]. The main reason for the high incidence of soil-borne diseases in croplands is the deterioration of the micro-ecological environment that can destroy or alter the balance of the soil microbial communities [76]. Therefore, attempts have been made to differentiate the microbial community composition and structure in the DSS from the DCS [77]. Microbiota change in relation to a local decrease in conduciveness to damping-off and other diseases caused by _R. solani_[78]. Maintaining dynamic microbial balance amongthe species, high microbial biomass and high biodiversity are key factors that can facilitate the development of DSS [79; 80; 81]. High biodiversity allows fewer resident pathogens to survive for long times and may also prevent the invasion of the exogenous ones. Several soil microorganisms can confer benefits in nutrient availability [82; 83] and can protect the host plant by preventing colonization and invasion of pathogen [23; 84]. There are two distinct models of disease suppresses differentiated by general and/or specific mechanisms. General suppression (GS) is a multi-trophic interaction that can be associated with the total microbial biomass in soil, affecting more than one pathogen simultaneously. GS exhibits non-specific mechanisms, such as offering basal protection against a broader spectrum of pathogens [85; 86] or biological buffering [87], GS is defined as the capacity of a soil to suppress the growth and activity of the pathogen up to certain level due to the antagonistic activity of the microbiomes fighting with the pathogens [22]. GS refers to disease suppression through competition between the resident soil microbiota and the pathogens for a common resource such as nutrient and space, and release of antibiotics and toxins from an active microbial consortium that hampers the growth and development of the pathogens [34]. Specific suppression (SS) is another type of disease suppression [88], which refers to the effects of an individual microorganism or a restricted group of microorganisms (or during specific stages of the pathogen life cycle) on suppression [89]. The main distinctive characteristic of SS is due to its transferability [90] from a suppressive soil into a conducive soil (from 1 to 10% by volume) that can be eliminated or reduced by sterilization or pasteurization at 55-60 \({}^{\circ}\)C for 30 min or irradiation with gamma rays [22; 76; 77]. It is important to recall that suppresses must be seen as a continuum from GS to SS [91]. However, GS includes antibiosis, competition, parasitism and predation, whileSS includes parasitism and predation of the pathogen by the dwelling microbes [92]. Authors have recently provided an interesting new perspective to explain both general and specific suppresses by using NGS of the microbiomes. Three soil suppressive models were proposed, \"take-all decline\" of wheat caused by _G. graminis_ var. _tritica_, \"damping-off\" by Rhizotonia bare patch of wheat and \"Streptomyces\" in suppression [25]. These authors proposed a number of hypotheses about the nature and ecology of microbial populations and communities of suppressive soils. Though authors have argued for limiting the term \"disease suppressiveness\" to situations involving only a clear biological component [93], there is plentiful evidence for the role of abiotic factors of soil involved in disease suppression [53; 58; 35]. The chemical and physical attributes can operate in suppression, either directly or indirectly, through their impacts on soil microbial activity. These attributes are largely influenced by different management practices, and thereby they can control the microbial population and diversity in the rhizosphere [94]. On basis of the durability of disease suppression, soils can be grouped into two further categories: \"induced suppression\" and \"long-standing suppression\" [71].