Plant Growth-Promoting Bacteria: Biological Tools for the Mitigation of Salinity Stress in Plants

Abstract

Salinity stress is one of the major abiotic stresses threatening sustainable crop production worldwide. The extent of salinity affected area is expected to cover about 50% of total agricultural land by 2050. Salinity stress produces various detrimental effects on plants’ physiological, biochemical, and molecular features and reduces productivity. The poor plant growth under salinity stress is due to reduced nutrient mobilization, hormonal imbalance, and formation of reactive oxygen species (ROS), ionic toxicity, and osmotic stress. Additionally, salinity also modulates physicochemical properties and reduces the microbial diversity of soil and thus decreases soil health. On the other hand, the demand for crop production is expected to increase in coming decades owing to the increasing global population. Conventional agricultural practices and improved salt-tolerant crop varieties will not be sufficient to achieve the yields desired in the near future. Plants harbor diverse microbes in their rhizosphere, and these have the potential to cope with the salinity stress. These salinity-tolerant plant growth-promoting bacteria (PGPB) assist the plants in withstanding saline conditions. These plant-associated microbes produce different compounds such as 1-aminocyclopropane-1-carboxylate (ACC) deaminase, indole-3-acetic acid (IAA), antioxidants, extracellular polymeric substance (EPS), and volatile organic compounds (VOC). Additionally, the naturally associated microbiome of plants has the potential to protect the host through stress avoidance, tolerance, and resistance strategies. Recent developments in microbiome research have shown ways in which novel microbe-assisted technologies can enhance plant salt tolerance and enable higher crop production under saline conditions. This focused review article presents the global scenario of salinity stress and discusses research highlights regarding PGPB and the microbiome as a biological tool for mitigation of salinity stress in plants.

Current Advances in Plant Growth Promoting Bacteria Alleviating Salt Stress for Sustainable Agriculture

“…Hence, the application of beneficial stress-tolerant microbes not only helps in improving the microbial community structure but also in enhancing plant and soil health under salinity. Further research will be required to reveal the hidden mechanisms of stress-tolerant microbial diversity [30]. Moreover, various researchers have demonstrated that the associations between rhizospheric microbes and stressed plants help the plants to adapt to their microenvironment [11].…”

Protection of Photosynthesis by Halotolerant Staphylococcus sciuri ET101 in Tomato (Lycoperiscon esculentum) and Rice (Oryza sativa) Plants During Salinity Stress: Possible Interplay Between Carboxylation and Oxygenation in Stress Mitigation

“…Salinity stress is the major environmental problem all over the world due to which the cultivable land area is decreased, and drastic reduction in root length, biomass, and growth is observed causing a decline in crop yields ( Deinlein et al, 2014 ; Janda et al, 2016 ; Kumar et al, 2020 ). The limitation of plant growth under salinity conditions is primarily due to reduction in photosynthesis rate and high intracellular accumulation of Na + ions, which interfere with various physiological processes ( Assaha et al, 2017 ; Analin et al, 2020 ).…”

“…Salinity stress-induced accumulation of excess salts is known to affect the function of photosystems by modulating the photosynthetic proteins in chloroplasts causing irreversible damage to the photosynthetic apparatus at all developmental stages in glycophytic plants ( Sun et al, 2016 ; Li et al, 2019 ; Rodríguez-Ortega et al, 2019 ; Zhang et al, 2020 ). Adaptation of plants to salinity stress involves modification of complex physiological traits, metabolic pathways, and gene networks ( Nounjan et al, 2012 ; Gupta and Huang, 2014 ; Ghorbani et al, 2018 ; Kumar et al, 2020 ). The key photosynthetic processes including RuBisCO enzyme activity, ATP generation, electron transport rate (ETR), and efficiency of light capture in the photosystems are seriously affected by salt stress ( Chaves et al, 2009 ).…”

Variability and salt tolerance screening of maize (Zea mays L.) inbred lines at seedling stage

“…Salinity stress is one of the major abiotic stresses threatening sustainable crop production worldwide. It is estimated that by 2050, world population will reach 9.6 billion and about 50% of agricultural land will be salinity affected [1][2] . Hence, global food productions will need to be increased 57% by 2050 to maintain current level of food supply 3 .…”

“…This makes the lands unsuitable for cultivation of crops. Salinity stress produces various detrimental effects on plants physiological, biochemical, and molecular features and reduces productivity 1 .…”