What Determines Successful Colonization and Expression of Biocontrol Traits at the Belowground Level?

Plant’s health and development are largely influenced by the microbiota inhabiting the rhizosphere soil, the root surface (rhizoplane) and the root endosphere compartments. This compound plant-associated belowground microbiome originates from surrounding bulk soil microbial communities. It is widely accepted that the structure and composition of this microbiota is shaped and modulated by: (i) the host plant immune response; (ii) root exudate-mediated signalling and plant metabolites; and (iii) the complex trophic relationships established among the components of these communities. These interactions, primarily during the initial colonization process, are crucial for the establishment of root-associated bacterial communities that largely differ from those of the enclosing soil. It is known that the belowground microbiota is a source of plant growth-promoting microorganisms (PGPM) and biological
control agents (BCA) that, once properly identified and carefully characterized, can be harnessed to improve plant fitness (Ciancio et al. 2016). Nevertheless, to reach this goal a comprehensive understanding of genetic determinants contributing to successful colonization of the target niche and effective biocontrol, as well as the wide range of factors influencing them, is needed (Cole et al. 2017).