The editors of the volume “PGPR and Medicinal Plants” asked me to write the Foreword to this book. I have gone through the volume contents and some chapters, which prompted me to write the Foreword. Microorganisms are abundantly distributed in the soil, ranging from bacteria, actinomycetes, fungi, algae, cyanobacteria, and protozoa. These microbes contribute many beneficial elements, like carbon, sulfur, phosphorus, and nitrogen, to the soil by taking part in the nutrient cycle. The zone of contact between the root and soil is the rhizosphere. This region has intense activity and concentration of microbes and is considered vital for plant vigor and full development to maturity. Plant growth and development promoting rhizobacteria (PGPR) are present in the vicinity of the root system and at times adhering to the root. Such bacteria have been applied to a wide range of agriculturally important crops for the purpose of plant growth promotion, including emergence seed germination and value addition. The influence of root exudates on the proliferation of soil microorganisms around and inside roots as well as interactions between soil microorganisms, rhizosphere colonies, and plant hosts have been widely studied. Studies based on molecular techniques have estimated about 4,000 microbial species per gram of soil samples. Powerful methods of estimation provide only the crudest measure of its magnitude. Nonetheless, many such estimates exist, suggesting that a single gram of soil may contain over 10 billion microbial cells and more than 1,800 bacterial species (Zhang et al. 2008). PGPRs are well established to colonize plant roots and stimulate plant growth. They serve the purpose of being used as biofertilizers, plant growth regulators, and biotic elicitors and promote plant growth by several mechanisms such as phosphorus solubilization, production of volatile organic compounds, induction of systemic disease resistance, nitrogen fixation, maintenance of soil fertility and n
