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It is now widely realized that excessive use of chemical fertilizers along with pesticides has led to progressive deterioration of soil health. Use of biofertilizers, in an integrated nutrient management program, is now considered to be an important ingredient for sustainable agriculture. Certain microorganisms found in the rhizosphere are known to improve soil fertility and consequently plant health and growth. Response of plants to inoculation with important soil bacteria, Azotobacter, Azospirillum, etc., in cereals often resulted in enhanced grain yield and plant biomass due to increased nutrient uptake, better expression of yield attributes like tiller numbers, plant height, leaf size, higher number of spikes and grains per spike, the thousand grain weight, increased root length and low incidences of plant diseases. The positive benefits from inoculation have been attributed to several mechanisms such as biological nitrogen fixation (BNF) (Kapulnik
et al., 1981a and 1981b; and Behl et al., 2006) and increased root uptake capacity because of enhanced root development and root hair formation (Behl et al., 2003 ) in response to secretion of plant growth hormones. Other mechanisms such as higher uptake of nitrate, phosphate and potassium (Kapulnik et al., 1985; and Narula et al., 2000) and stimulation of NO3 assimilation due to inoculation (Boddey et al., 1986) are also believed to increase yields. Some plant genotypes have developed response mechanisms that help in extracting phosphorus and micronutrients more effectively from rhizobacteria (Singh et al., 2007; and Singh et al., 2008). Azotobacter supply nutrients to plants by degrading organic matter, convert atmospheric nitrogen into a usable form, protect plants from disease and stimulate plant growth. Beneficial plant-microbe interactions and the stability and effectiveness of biofertilizers depend upon the establishment of bacterial strains in the rhizosphere of the plant (Kukreja et al., 2004; and Narula et al., 2005). Therefore, it is imperative to evaluate complementarities between varietal behavior of wheat to Azotobacter chroococcum strains in terms of agronomical parameters and to identify root exudates that determine specificity of interactions.
The present studies were conducted to determine wheat-Azotobacter interaction under pot house conditions using two strains of A. chroococcum with differences in quality and quantity of phytohormone production (Kumar et al., 2001a) and genetically divergent six wheat varieties varying for shoot and root traits and their performance under rainfed, low input and high input conditions.
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