Rhizosphere and Root Colonization by Bacterial Inoculants and Their Monitoring Methods: A Critical Area in PGPR Research

Abstract

Roots serve a multitude of functions in plants including anchorage, acquisition of nutrients and water, and production of exudates with growth regulatory properties. The root-soil interface, or rhizosphere, is the site of greatest biological and chemical activity within the soil matrix. Plant growth-promoting rhizobacteria (PGPR) are known to influence plant health by controlling plant pathogens or via direct enhancement of plant development in the laboratory and in greenhouse experiments. Unfortunately, however, results in the field have been less consistent. The colonization of roots by inoculated bacteria is an important step in the interaction between beneficial bacteria and the host plant. However, colonization is a complex phenomenon influenced by many biotic and abiotic parameters, some of which are only now apparent. Monitoring fate and metabolic activity of microbial inoculants as well as their impact on rhizosphere and soil microbial communities are needed to guarantee safe and reliable application, independent of whether they are genetically modified or not. The first and most crucial prerequisite for effective use of PGPRs is that strain identity and activity are continuously confirmed. A combination of both classical and molecular techniques must be perfected for more effective monitoring of inoculants strain (both genetically modified and unmodified) after release into the soil. Recent developments in techniques for studying rhizobacterial communities and detection and tracking systems of inoculated bacteria are important in future application and assessment of effectiveness and consistent performance of microbial inoculants in crop production and protection.

Pseudomonas spp. isolates with high phosphate-mobilizing potential and root colonization properties from agricultural bulk soils under no-till management

“…The failure of PGPR to produce the desired effects in the field after seed inoculation is frequently associated with their poor rootcolonizing ability (Ahmad et al 2011;Barrett et al 2011). The study of root colonization by inoculated bacteria therefore provides an important criterion of strain selection for the formulation of efficient PGPR inoculants.…”

A review: what is the spermosphere and how can it be studied?

“…; Ahmad et al . ). This method can also be used for to characterize nutrient availability at specific microsites after extraction from soil or in situ .…”

“…To overcome the risk of similar molecular markers in native strains, methods based on the detection of polymorphism in the genome involving a PCR step were tested: amplified fragment length polymorphism, single strand conformation polymorphism (SSCP) and random amplified polymorphic DNA (Ahmad et al . ; Marschner et al . ).…”

Effects of growth-promoters on the productivity of <i></i><i>Arundo donax</i><i></i> L. (NileFiber™) grown as a purpose-grown biofuel feedstock in Nova Scotia

“…Root colonization is the most basic yet important step in establishing a beneficial relationship between plants and promoters (Ahmad et al 2011;Mangmang et al 2015). The delayed soil drench treatment of NileFiber™ could have enabled native microorganisms to colonize root systems and establish their rhizospheric role prior to the supplemental exogenous GP application (Schippers et al 1987;Requena et al 1997).…”