![]() ![]() As a result of increasing urbanization and industrialization, threats to the environment have increased, leading to the shrinkage of agricultural land on one hand and causing significant declines in crop growth on the other hand. The Food and Agricultural Organization has provided an estimate of the alarmingly increasing human population, expected to reach 8–9 billion by 2030 ( FAO, 2010). This review will therefore be helpful to plant physiologists and agricultural microbiologists in designing strategies and tools for the development of broad spectrum microbial inoculants supporting sustainable crop production under hostile environments. In doing so, this review highlights important plant morpho-physiological traits that can be exploited to identify the positive effects of phytohormones on stress tolerance. We focus on recent successes in identifying the roles of microbial phytohormones that induce stress tolerance, especially in crop plants. Here, we review current knowledge on the function of phytohormones involved in the improvement of abiotic stress tolerance and defense response in plants exposed to different stressors. Phytohormone biosynthetic pathways have been identified using several genetic and biochemical methods, and numerous reviews are currently available on this topic. Recent investigations have shown that phytohormones produced by root-associated microbes may prove to be important metabolic engineering targets for inducing host tolerance to abiotic stresses. Exogenous phytohormone supplementation has been adopted to improve growth and metabolism under stress conditions. Phytohormones are among the most important growth regulators they are known for having a prominent impact on plant metabolism, and additionally, they play a vital role in the stimulation of plant defense response mechanisms against stresses. Plants employ several tolerance mechanisms and pathways to avert the effects of stresses that are triggered whenever alterations in metabolism are encountered. Abiotic stresses have negative impact on the physiology and morphology of plants through defects in the genetic regulation of cellular pathways. Plants are subjected to various abiotic stresses, such as drought, extreme temperature, salinity, and heavy metals. 4Mycology and Plant Disease Survey Department, Plant Pathology Research Institute, Giza, Egypt.3Botany and Microbiology Department, College of Science, King Saud University, Riyadh, Saudi Arabia.2Plant Production Department, College of Food and Agricultural Sciences, King Saud University, Riyadh, Saudi Arabia.1Leibniz Centre for Agricultural Landscape Research, Institute of Landscape Biogeochemistry, Müncheberg, Germany. ![]()
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