The aim of the present review is to study the effect of plant growth promoting rhizobacteria (PGPR) on crops. These PGPRs are meant to be the natural and alternate substitute of chemicals in agriculture. The plant growth promoting rhizobacteria are the naturally occurring soil bacteria which enhance the plant growth, also protect plant in stress condition without causing any adverse effect on the environment. The use of PGPRs for sustainable and safe agriculture has increased globally in last couple of decades. PGPRs are meant to reduce the soil toxicity which occurs due to surplus use of chemicals and pesticides. Scientific researches involve multidisciplinary approaches to understand the working of PGPR, effects on plant growth and physiology, biocontrol of plant pathogens, induced systematic resistance and phyto-stimulation. PGPR had shown both antagonistic and synergistic interaction with their surrounding microorganism to boost the plant favorably. The present review has tried to describe all the important aspects of PGPRs and thus can be described as revolutionized tools for farmers for sustainable agriculture.

Silicon is the second most abundant element in the earth's crust, and hence is plentiful in most soils.Silica is absorbed by plants as silicic acid, with cereals and grasses containing the highest concentrations (0.2-2.0%).Most soils contain significant quantities of silica, but continuous cropping, particularly with crops that accumulate significant quantities of silica, can reduce plant available levels of Si to the point that supplemental Si fertilization is required.There appears to be a need for Si amendments in temperate as well as tropical crop production systems, and Si fertilizers are applied to crops in several countries for increased productivity and sustainable production.High silica uptake has been shown to improve drought resistance, increase resistance to fungi and other pathogens, and increase plant growth rate and yield.However, its essentiality as a micronutrient for higher plants is difficult to prove, partly due to the fact that many positive effects of Si are most apparent in cases of abiotic stresses.Silica amendments have also been shown to correct soil toxicities resulting from high levels of soluble Mn 2+ , Fe 2+ , and Al 3+ .Most plants groups are known to deposit silica between the cells and tissues in solid form creating amorphous structures called Phytoliths or Silica bodies.Phytoliths are formed after absorbing silica in soluble form, as is offered in Biological silica.They provide mechanical strength and rigidity to plant parts and act as defence system against insects, pests and fungal infestations as well as improve water balance, plant growth and yield, rates of photosynthesis and reproduction.Silica acts as immune-stimulator within crops thus enable the enhancement of defence mechanism in crops.Silica enables the plants build up a physical mineral barrier lining the cell.This makes it difficult for biting and sucking bugs to damage the plants.Naturally this reduces the food intake, growth longevity and population growth ofxylem feeding insects and other pathogens.It has been observed that plants accumulate Silica around fungal infected sites.If the plant has sufficient silica level, it creates an active defence against fungal infections as well.From last few decade silicon is getting great attention due to its abundance and non-hazardous nature.Silicon nutrition is found to be very helpful providing resistance to crops against biotic and abiotic stresses.Silicon also provide resistance to the plants against pathogens.The present review is thus attempted to define nature of silica, its compatibility with crops and applications of silica in enhancement of agricultural productivity in terms of sustainable agriculture.