Abstract
Due to the rapid growth of population, the demand for food is set to rise by 60% by 2030. Chemical fertilizers have been used extensively to enhance crop productivity to meet this demand, resulting in deterioration of the environment. Rhizospheric microorganisms maintain a close relationship with plants and help stimulate plant growth. Arbuscular mycorrhizal fungi are ubiquitous and form a symbiotic association with many higher plants. They improve mineral nutrient uptake and enhance abiotic stress tolerance. Plant growth promoting rhizobacteria (PGPR) colonize the root zone and provide beneficial effects. Azotobacter is a diazotrophic plant-growth promoting rhizobacteria that stimulates plant growth through nitrogen fixation and production of stimulating substances. Both these microorganisms have been extensively used in supplementing the nutrient demand of the crop, thereby reducing dependence on chemical fertilizers. Root-parasitic nematodes reduce productivity of most cultivated plants throughout the world. Root-parasitic nematodes are endoparasites and enter through the roots. Mycorrhizal fungi protect the plants from damages caused by root-parasitic nematodes. In general, pre-inoculation with mycorrhizal fungi leads to reduced nematode population, improves plant growth and nutrient uptake. Glomus fasciculatum is most efficient in suppressing nematode population. The antagonistic effect of Azotobacter on nematode development and multiplication in the host plant has been observed. Organic amendments including oil-seed cakes and botanicals have also been used for reducing the severity of nematode infestation. Synergistic interaction of arbuscular mycorrhizal fungi with other bioinoculants, nematicides and organic amendments on nematode suppression has been observed. Plant growth promoting and biocontrol traits along with induction of systemic resistance are the main disease protection mechanisms of bio-inoculants. Whereas organic amendments suppress nematode population in soil by modifying soil physical properties, producing nematicidal compounds and antagonistic secondary metabolites. Depending on the identity of the interacting fungal partner and the insect, both negative as well as positive impacts of arbuscular mycorrhizal fungi colonization on root-feeding insects have been observed.