Seed coating is seen as the best approach, as it enables the BCA to be positioned close to the seedlings and good colonization of the rhizosphere of the plant can be expected (Bennett &Whipps, 2008). Whatever the modes of action of the BCA, the success of biological control depends on the activity of the BCA at the root level, in the rhizosphere. Rhizosphere competence is a criterion that must be taken into account early during the screening process. There exist great differences in the ability to colonize the rhizosphere of the plant even among strains belonging to the same species. Moreover, this capacity is plant specific, and therefore a given BCA might be effective in controlling a given pathogen in one crop but not in another.
The last issue to be addressed is that of integration of biological control with other cultural practices. Such integration requires a holistic approach, taking into account all the components of the agro-ecosystem, at the scale of the farm or even at the landscape level.
To conclude, in our opinion, if biological control is to be successful more research is required, not only to elucide modes of action at the molecular level, but also to characterize the ecological fitness of the BCAs, and to improve the production, formulation and application processes.