Plant growth-promoting rhizobacteria (PGPR) are under extensive investigation, especially in developing countries, as supplements of chemical fertilizers due to cost-effective and eco-friendly nature. The competence and consistency of PGPR in heterogeneous soil medium and diverse ecological settings are still unclear. The current study presents in vitro and field evaluation of a physiologically and genetically characterized PGPR strain Enterobacter sp. Fs-11 (GenBank accession # GQ179978) in

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... ms of its potential to thrive in rhizosphere and enhance sunflower crop yield and oil contents under diverse environmental conditions. Under in vitro conditions, strain Fs-11 was found to grow optimally at a range of temperature (15 to 40 °C) and pH values (6.5 to 8.5). Extracellular and intracellular localization of the strain Fs-11 in sunflower root cortical cells through transmission electron microscopy confirmed its epiphytic and endophytic root colonization pattern, respectively. In field experiments, conducted at three different agro-climatic locations, inoculation of strain Fs-11 at 50% reduced NP-fertilizer resulted in a significant (Fisher's LSD; P≤0.05) increase in growth, achene yield, nutrient uptake and oil contents as compared to non-inoculated plants. Inoculation also responded significantly in terms of increase in mono and polyunsaturated fatty acids (oleic and linoleic acids, respectively) without rising saturated fatty acid (palmitic and stearic acid) contents. We concluded that Enterobacter sp. Fs-11 is a potential candidate for biofertilizer formulations to supplement chemical fertilizer requirements of sunflower crop under diverse climatic conditions.