Action is needed to face the global threat arising from inconsistent rainfall, rise in temperature, and salinization of farm lands which may be the product of climate change. As crops are adversely affected, man and animals may face famine. Plants are severely affected by abiotic stress (drought, salinity, alkalinity, and temperature), which impairs yield and results in loss to farmers and to the nation at large. However, microbes have been shown to be of great help in the fight against abiotic stress, via their biological activities at the rhizosphere of plants. The external application of chemical substances such as glycine betaine, proline, and nutrients has helped in sustaining plant growth and productive ability. In this review, we tried to understand the part played by bioinoculants in aiding plants to resist the negative consequences arising from abiotic stress and to suggest better practices that will be of help in today’s farming systems. The fact that absolute protection and sustainability of plant yield under stress challenges has not been achieved by microbes, nutrients, nor the addition of chemicals (osmo-protectants) alone suggests that studies should focus on the integration of these units (microbes, nutrients, chemical stimulants, and osmo-protectants) into a strategy for achieving a complete tolerance to abiotic stress. Also, other species of microbes capable of shielding plant from stress, boosting yield and growth, providing nutrients, and protecting the plants from harmful invading pathogens should be sought.

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The influence of plant growth-promoting rhizobacteria in plant tolerance to abiotic stress: a survival strategy.

The rhizosphere is the region around plant roots where maximum microbial activities occur. In the rhizosphere both beneficial and harmful activities of microorganisms affect plant growth and development. The mutualistic rhizospheric bacteria which improve the plant growth and health are known as plant growth-promoting rhizobacteria (PGPR). They are of much importance due to their ability to help the plant in diverse manners. PGPR such as Pseudomonas, Bacillus, Azospirillum, Azotobacter, Arthrobacter, Achromobacter, Micrococcus, Enterobacter, Rhizobium, Agrobacterium, Pantoea, and Serratia are now very well known. Application of PGPR as bioinoculants/bioformulations is found to be very effective in enhancing crop productivity in a sustainable way. The use of PGPR in agriculture is also ecologically important as the synthetic chemicals used in agriculture are a severe threat to agroecosystems.

Plant Growth-Promoting Rhizobacteria: Diversity and Applications

Plant and soil microbiome interactions are in the great demand around the globe. Bacteria that colonize in the plant roots or in the rhizosphere and promote plant growth directly by nutrient immobilization or worked as defense regulator are referred to as plant growth-promoting rhizobacteria (PGPR). During the past couple of decades, PGPR have emerged as a potent alternative to chemical fertilizer in an eco-friendly manner. Therefore, they are abundantly accepted in agriculture, horticulture, silviculture, and environmental cleanup strategies. The rhizosphere ecology is influenced by a myriad of abiotic and biotic factors in natural and agricultural soils, and these factors can, in turn, modulate PGPR effects on plant health. Manipulating this rhizospheric microbiome through rhizo-engineering has materialized as a contemporary methodology to decipher the structural, functional, and ecological behavior of rhizospheric PGPR populations. In this chapter, we have tried to explore the latest developments in the technologies related to PGPR, for its well acceptance for sustainable agriculture and plant health.

Plant Growth Promoting Rhizobacteria (PGPR): Modern Prospects for Sustainable Agriculture

World population growth, together with climate changes and increased hidden hunger, bring an urgent need for finding sustainable and eco-friendly agricultural approaches to improve crop yield and nutritional value. The existing methodologies for enhancing the concentration of bioavailable micronutrients in edible crop tissues (i.e., biofortification), including some agronomic strategies, conventional plant breeding, and genetic engineering, have not always been successful. In recent years, the use of plant growth-promoting bacteria (PGPB) has been suggested as a promising approach for the biofortification of important crops, including legumes. Legumes have many beneficial health effects, namely, improved immunological, metabolic and hormonal regulation, anticarcinogenic and anti-inflammatory effects, and decreased risk of cardiovascular and obesity-related diseases. These crops also play a key role in the environment through symbiotic nitrogen (N) fixation, reducing the need for N fertilizers, reducing CO2 emissions, improving soil composition, and increasing plant resistance to pests and diseases. PGPB act by a series of direct and indirect mechanisms to potentially improve crop yields and nutrition. This review will focus on the: (i) importance of legumes in the accomplishment of United Nations Sustainable Development Goals for production systems; (ii) understanding the role of PGPB in plant nutrition; (iii) iron biofortification of legumes with PGPB, which is an interesting case study of a green technology for sustainable plant-food production improving nutrition and promoting sustainable agriculture.

https://www.mdpi.com/2073-4395/10/3/435/pdf

Legume Biofortification and the Role of Plant Growth-Promoting Bacteria in a Sustainable Agricultural Era

Growth-promoting rhizobacteria are free-living bacteria that colonize the roots and stimulate the plant growth. Many of these bacteria secrete a range of extracellular metabolites that can be involved in the biological control of plant pathogens. In this study, the effect of four plant growth-promoting rhizobacteria (PGPR) was evaluated on tomato growth parameters as well as biological control of the root-knot nematode (RKN) (Meloidogyne javanica). Tomato seedlings were inoculated with four isolates of PGPR including Pseudomonas fluorescens, Pseudomonas striata, Bacillus subtilis, and Paenibacillus polymyxa and cultivated in the presence or absence of RKN. The results showed that the PGPR significantly increased the plant growth parameters. Bacterial strains also significantly affected the reproductive factor of Meloidogyne javanica significantly so that P. fluorescens and B. subtilis reduced the reproductive factor from 112.15 to 24.94 and 24.96, respectively. Based on these results, among applied rhizobacteria in this study, P. polymyxa can be regarded as the best candidate for promoting the growth and biological control of M. javanica in tomato crop under greenhouse conditions.

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Evaluation of four rhizobacteria on tomato growth and suppression of root-knot nematode, Meloidogyne javanica under greenhouse conditions, a pilot study

Plant Growth promoting rhizobacteria are a heterogeneous group of bacteria that can be found in the rhizosphere, at root surfaces and in association with roots. They benefit plants through Production of plant hormones, such as auxins, asymbiotic N2 fixation, solubilization of mineral phosphates, antagonism against phytopathogenic microorganisms by production of antibiotics, siderophroes, Chitinase and other nutrients ability to effectively colonize roots are responsible for plant growth promotion. An experiment was conducted in the field of National Institute of Agronomic Research of Meknes. Morocco. The experiment was a completely randomized design with six replicates. There were four treatments viz. T1: (control; N0 -PGPR), T2: (N0 +2027-2), T3: (N0 +2066-7) and T4: (N0+2025-1). The results indicated that a remarkable increase in root growth, namely length, the diameter of the rod and the total chlorophyll. A total of three different bacteria colonies were isolated and proceed with in vitro screening for plant growth promoting activities; phosphate solubilization, nitrogen fixation, indole acetic acid (IAA), ammonia production and antimicrobial enzymes (cellulose, chitinase and protease) activity. Among the three bacterial strains, all bacterial strains are able to produce ammonia, IAA production and nitrogen fixation activity, one strain phosphate solubilizing activity, two strain are able to produce cellulase syntheses, Protease activity and Chitinase activity.

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Effect of plant growth promoting rhizobacterial (PGPR) inoculation on growth in tomato (Solanum Lycopersicum L.) and characterization for direct PGP abilities in Morocco

R Elkahkahi

Papers

Effect of plant growth promoting rhizobacterial (PGPR) inoculation on growth in tomato (Solanum Lycopersicum L.) and characterization for direct PGP abilities in Morocco