PGPR Mediated Alterations in Root Traits: Way Toward Sustainable Crop Production

Abstract

The above ground growth of the plant is highly dependent on the belowground root system. Rhizosphere is the zone of continuous interplay between plant roots and soil microbial communities. Plants, through root exudates, attract rhizosphere microorganisms to colonize the root surface and internal tissues. Many of these microorganisms known as plant growth promoting rhizobacteria (PGPR) improve plant growth through several direct and indirect mechanisms including biological nitrogen fixation, nutrient solubilization, and disease-control. Many PGPR, by producing phytohormones, volatile organic compounds, and secondary metabolites play important role in influencing the root architecture and growth, resulting in increased surface area for nutrient exchange and other rhizosphere effects. PGPR also improve resource use efficiency of the root system by improving the root system functioning at physiological levels. PGPR mediated root trait alterations can contribute to agroecosystem through improving crop stand, resource use efficiency, stress tolerance, soil structure etc. Thus, PGPR capable of modulating root traits can play important role in agricultural sustainability and root traits can be used as a primary criterion for the selection of potential PGPR strains. Available PGPR studies emphasize root morphological and physiological traits to assess the effect of PGPR. However, these traits can be influenced by various external factors and may give varying results. Therefore, it is important to understand the pathways and genes involved in plant root traits and the microbial signals/metabolites that can intercept and/or intersect these pathways for modulating root traits. The use of advanced tools and technologies can help to decipher the mechanisms involved in PGPR mediated determinants affecting the root traits. Further identification of PGPR based determinants/signaling molecules capable of regulating root trait genes and pathways can open up new avenues in PGPR research. The present review updates recent knowledge on the PGPR influence on root architecture and root functional traits and its benefits to the agro-ecosystem. Efforts have been made to understand the bacterial signals/determinants that can play regulatory role in the expression of root traits and their prospects in sustainable agriculture. The review will be helpful in providing future directions to the researchers working on PGPR and root system functioning.

The Contrivance of Plant Growth Promoting Microbes to Mitigate Climate Change Impact in Agriculture

“…PGPB isolated only from the root zone, on the other hand, are called plant growth promoting rhizobacteria (PGPR) [ 18 , 21 ]. It has been estimated that only 2 to 5% of rhizosphere bacteria exhibit PGPR properties ( Table 1 ) [ 115 ]. PGPB can be used effectively under conditions of nutrient deficiency and are gradually replacing fertilizers.…”

“…The beneficial effects on the plant through interaction with PGPB can be achieved both directly as well as indirectly [ 10 , 79 ]. Direct mechanisms are based on the production of plant growth promoting substances or biofertilization by mobilizing mineral soil components [ 115 ]. These processes have a decisive influence on the condition of the plant and their development [ 6 , 9 , 80 , 81 , 82 ].…”

“…Phytohormones produced by bacteria can act as plant growth regulators involved in plant development, physiology and immunity [ 123 ]. PGPB can synthesize auxins, gibberellins, cytokinin and abscisic acid [ 2 , 99 , 100 , 108 , 115 ]. Auxins, especially indole-3-acetic acid (IAA) produced by PGPB, can stimulate root growth, nodulation and cell proliferation [ 7 , 56 ].…”

“…Auxins, especially indole-3-acetic acid (IAA) produced by PGPB, can stimulate root growth, nodulation and cell proliferation [ 7 , 56 ]. Synthesis of auxin has been demonstrated several times by different strains, mainly represented by the genera: Bacillus , Burkholderia , Serratia , Aeromonas and Azospirillum [ 115 ]. Some PGPB are also cytokinin and gibberellin producers, but further research is needed to determine the role of these bacterial hormones in plant growth [ 2 , 13 , 124 ].…”

The Effects of Biostimulants on Induced Plant Defense

“…Currently these products include extracts of seaweed, humic substances (humic acids and fulvic acids), chitin and chitosan derivatives, amino acids, protein hydrolysates, and microbes (Al-Juthery et al, 2020). Some have been showing promise for commercial agriculture, not only for enhancing plant growth above-and below-ground and/or crop productivity as it has been reported currently (Grover et al, 2020;Jiménez-Arias et al, 2021;Sakr et al, 2021), but also more specifically in enhancing plant defense against pests and pathogens (Brown and Saa, 2015).…”