Exploiting Plant Growth Promoting Rhizomicroorganisms for Enhanced Crop Productivity

Abstract

The increasing pressure on land resources has made it imperative for vertical growth through enhanced crop intensity and productivity. To meet this challenge, appropriate integrated nutrient and pest management packages must be confi gured for different agro-ecological conditions. By 2050, the crop nitrogen demand is expected to reach 40-45 million tonnes. To meet such enormous nitrogen requirements through chemical fertilizers, would not only be expensive but also could severely degrade soil health. Similar is the situation with other macro-and micro-nutrients. The rhizosphere environment, at the interface between root and soil, is a major habitat for soil processes. Rhizosphere biology is approaching a century of investigations, wherein growth-promoting rhizomicroorganisms such as Rhizobium , Azotobacter, Pseudomonas, Bacillus, Azospirillum, Frankia and mycorrhizal fungi have attracted special attention on account of their benefi cial activities. Plant growth promoting rhizomicroorganisms (PGPR) include diverse microbes that infl uence plant health by colonizing roots, enhancing plant growth, reducing plant pathogen populations and activating plant defenses against biotic stresses. PGPRs promote plant growth in different ways such as infl uencing plant hormonal balance, antagonistic to pathogens through various modes, stimulation of plant resistance/defense mechanisms, effects nutrient uptake by secretion of organic acids or protons to solubilize nutrients, atmospheric N 2 fi xation and by modifying rhizospheric soil environment by exo-polysaccharides production. Though research was going on in isolation in the above areas, with the advent of a core group for PGPR research, the pace in this direction has signifi cantly increased. The primary emphasis on exploiting the vast biodiversity of microorganisms to identify the

Using two plant growth promoting bacteria to sustainably reduce the drought-induced loss in Triticum aestivum yield

“…For instance, Treating plants with PGPB has been reported to: 1) induce favorable alterations in root growth and architecture (longer roots, longer and denser lateral roots and higher biomasses) (Naseem and Bano, 2014;Timmusk et al, 2014); 2) improve shoot growth (higher shoots and heavier biomasses) (Kasim et al, 2013;Grover et al, 2014); 3) maintain relatively higher relative water contents than the drought-stressed and bacterially-untreated plants (Sandhya et al, 2010;Naveed et al, 2014;Naseem and Bano, 2014); 4) facilitate water and nutrient (e.g. Fe, P and N) acquisition (Desai et al, 2012;Ngumbi and Kloepper, 2016); 5) modulate the plant hormones levels either by synthesizing phytohormones or by lowering the plant-produced ethylene via the ACC-deaminase activity (Castillo et al, 2013;Bresson et al, 2013;Ngumbi and Kloepper, 2016); 6) stabilize membranes (Gusain et al, 2015); and 7) regulate each of expression of some drought-triggered genes (Kasim et al, 2013;Sarma and Saikia, 2014), production of osmolytes (Bano et al, 2013;Gururani et al, 2013), and activities of different enzymes (Kohler et al, 2008) resulting in promoted plant growth and productivity under drought stress (Vurukonda et al, 2016;Forni et al, 2017). Moreover, inoculating the salt-stressed barely with A. brasilense NO40 significantly ameliorated the adverse effect of salinity on growth and yield (Omar et al, 2009), but no available studies illustrating the role of S. maltophila in augmenting crop yields under abiotic stressed conditions.…”

Rhizobacteria antagonistic to the fungus Sclerotium cepivorum (Berk.t) in onion plants (Allium cepa L.)

“…The soil is a complex system of beneficial effects due to interactions with rhizobacteria, which depend on both the strain and the plant; the genus Bacillus, has influence on variable of plants of the type of mini-tubers and tubers. Alvarado-Capo et al, (2015), who worked with potatoes, mention that Bacillus has the advantage of forming endospores which gives great stability to act as biofertilizers or biofungicides (Desai et al, 2012) and allow them to resist adverse environmental conditions, favoring the storage of products (Moreno et al, 2018). Rhizobacteria favor root length and fresh weight and dry weight in onion plants, which coincides with the results of Angulo-Castro et al, (2018), who worked on the application and inoculation of bacterial strains in plants, demonstrating that there was greater development in plant height, leaf area, stem diameter and radical volume, they demonstrated that rhizospheric and endophytic bacteria stimulate the emergence and growth of seedlings of this species.…”

“…Other mechanisms act to reduce the harmful effect of phytopathogens through the production of antagonistic substances (tetrasulfides, thiols, thiophenes and sulfur dioxide) and as producers of siderophores that sequester the iron present in the medium (Corrales-García and Ciro, 2010;Glick, 2014), as has been demonstrated, in the different mechanisms of action of a bacterial biological compound that limits the development of pathogens as indicated by the Fungicide Resistance Committee (FRAC, 2018). However, the selection of microorganisms is based on the capacity for increased production of metabolites of interest or antagonistic factor, on the use of organic substances as a source of nutrients and on the energy that allows them to survive and efficiently prevent the proliferation of phytopathogens, acting through the synthesis of antibiotics, or enzymatic biocontrol processes (Desai et al, 2012), important for agriculture especially in vegetable crops.…”