ABSTRACT
The rhizosphere represents a highly dynamic and complex interface for chemical, physical, and biological interactions. Various types of interactions occur between roots and soil organisms, which may be positive, negative, or neutral. Root exudates have a major role in determining outcomes of interactions in the rhizosphere. In natural settings, roots are in continual communication with neighboring plant species and quickly recognize and prevent the presence of invading roots through chemical messengers. Resource competition, chemical interference, and/or parasitism lead to negative interactions between plants. Plant-beneficial microbial interactions are with nutrient mobilizers, biocontrol agents, plant growth promoters, and neutral interactions. The rhizosphere is the playground and infection court where soil borne pathogens establish a parasitic relationship with the plant and among the complex rhizosphere community. Competition, antagonism, induced resistance, hyperparasitism, plant growth promotion, biological control, biofertilization are some of the interactions commonly observed in the rhizosphere. Most land plants form a symbiotic association with mycorrhiza, which play a key role in bridging the gap in the plant–soil interface with an extensive external mycelial network. Various beneficial rhizobacteria like Azotobacter and Gluconacetobacter have been evaluated for their antagonistic effect on a variety of plant parasitic nematodes.
