Beneficial microbial allelopathies in the root zone: the management of soil quality and plant disease with rhizobacteria

By virtue of their physiological adaptability and metabolic versatility, bacteria in plant root zones are a key agent of change in soil agroecosystems. Interactions between plant root systems and rhizobacteria have a profound effect on crop health, yield, and soil quality. Through the selective release of exudates and leachates plants activate and sustain specific rhizobacterial communities in the root zone. In turn, root zone bacteria are able to generate a wide array of secondary metabolites which can have a positive influence on plant growth; enhancing the availability of minerals and nutrients, improving nitrogen fixation ability, decreasing susceptibility to frost damage, improving plant health through the biocontrol of phytopathogens, inducing systemic plant disease resistance, and facilitating plant establishment, growth and development. The benefits from root zone bacterial biodiversity are moot in managed agroecosystems, where community complexity is minimized, and ecosystem stability is often disrupted for the purpose of disease control and yield maximization. The complexity of plant–soil–microbial interactions are so varied, that a complete understanding of all the relationships involved is unlikely to be achieved, even in a production monoculture. Nevertheless, the consequences of beneficial biological interactions that stimulate crop yields and improve plant health can be evaluated relatively simply and a number of general management strategies can be devised accordingly.