Role of Plant Growth-Promoting Rhizobacteria (PGPR) in the Improvement of Vegetable Crop Production Under Stress Conditions

Abstract

Biotic and abiotic stresses are major constrains to agricultural production. Among abiotic stress, drought and salinity are the major environmental factors limiting growth and productivity of many crops including vegetables, particularly in arid and semiarid areas of the world. Abiotic stress causes more than 50% average yield loss worldwide. Globally, demand for vegetables is increasing, and this has boosted the vegetable production in recent times. The substantial increase in production of key vegetables such as tomato, onion, cucumber, eggplant, cauliflower, pepper, lettuce, carrot, and spinach has been recorded. However, vegetables are generally considered more vulnerable than staple crops to stressful environmental conditions including extremes of temperature, drought, salinity, water logging, mineral nutrient excess and deficiency, and changes in soil pH which are likely to be exacerbated by the prevalent climatic change in many parts of the world. Plant growth under stress conditions on the contrary may be enhanced by the application of microbial inoculation including plant growth-promoting rhizobacteria (PGPR). These microbes promote plant growth by regulating nutritional and hormonal balance, producing plant growth regulators, solubilizing nutrients, and inducing resistance against plant pathogens. In addition to their interactions with plants, these microbes exhibit synergistic as well as antagonistic interactions with other soil microbiota. These interactions are vital to maintain soil fertility and concurrently the growth and development of vegetables under stress conditions. The present literature comprehensively discusses recent developments on the effectiveness of PGPR in enhancing vegetable growth under stressful environments.