Intensification farming practice which mainly depends on agrochemical fertilizers and pesticides to meet the global food demand causes many problems to the environment. For instance, the high rate of synthetic nitrogen fertilizers utilization in the farmlands could damage the environment through some chemical and biological processes such as leaching, run-off, and volatilization.
The world needs to find alternative ways in order to solve the food security problem. In this case, harnessing microbes is a good choice since it is a more eco-friendly and powerful technology that can be used to enhance agricultural production. In particular, this kind of technology is termed as ‘Microbial farming’.
There are many reports and publications talking about the successful application of microbial farming. For example, using Plant Growth-Promoting Rhizobacteria (PGPR) or Plant Growth-Promoting Microbes (PGPM) that have ability regulating hormonal and nutritional balance, inducing resistance against plant pathogens, and solubilizing nutrients for easy uptake by plants, resulting in the growth promotion of the plants.
Nutrient Acquisition by PGPR. Microbes that assist in plant nutrient acquisition act through a variety of mechanisms including augmenting surface area accessed by plant roots, nitrogen fixation, P-solubilization, siderophore production and HCN production. Therefore, manipulating microbial activity has great potential to provide crops with nutritional requirements.
Plant Hormones Produced by PGPR. Phytohormones are key players in regulating plant growth and development. They also function as molecular signals in response to environmental factors that otherwise limit plant growth. Many PGPR can produce auxins to exert particularly strong effects on root growth and architecture. Indole-3-acetic acid (IAA) is the most widely studied auxin produced by PGPR. Vast majority of PGPR also produce cytokinins and gibberellins but the role of bacterially synthesized hormones in plants, and bacterial mechanism of synthesis, are not yet completely understood. Some strains of PGPR can promote relatively large amounts of gibberellins, leading to enhanced plant shoot growth. Interactions of these hormones with auxins can alter root architecture.
Ethylene is a gaseous hormone, active at extremely low concentrations (0.05 mL L-1) and is a stress hormone. At high concentrations, ethylene induces the defoliation and cellular processes that lead to the inhibition of root and stem growth together with premature senescence, all of which lead to poorer crop performance. Thus, PGPR secrete 1-aminocyclopropane-1-carboxylase (ACC) deaminase which reduces ethylene production in plants. Many studies have shown enhanced stress tolerance in plants through inoculation with PGPR that produce ACC deaminase. This appears to occur since PGPR are able to keep ethylene levels from reaching levels sufficient to reduce plant growth, as has been demonstrated with Camelina sativa.
Production of Siderophores by PGPR. Iron is among the bulk minerals present on the surface of the earth, yet it is unavailable in the soil for plants. Iron is commonly present in nature in the form of Fe3+, which is highly insoluble; to solve this problem, PGPR secrete siderophores. Siderophores are low molecular weight iron binding protein compounds involved in the process of chelating ferric iron (Fe (iii)) from the environment. When Fe is limited, microbial siderophores provide plants with Fe, enhancing their growth.
Production of Volatile Organic Compound (VOC) by PGPR. VOCs produced by plant PGPR are heavily involved in improving plant growth and induce systemic resistance (ISR) towards pathogens. Several bacterial species, from different genera including Bacillus, Pseudomonas, Serratia, Arthrobacter, and Stenotrophomonas, produce VOCs that influence plant growth. Acetoin and 2,3-butanediol synthesized by Bacillus are the best known of these compounds and are responsible for significant improvements in plant growth. Some other PGPR strains emit VOCs that can directly and/or indirectly mediate increases in plant biomass, disease resistance, and abiotic stress tolerance. VOC emission is indeed a common property of a wide variety of soil microorganisms, although the identity and quantity of volatile compounds emitted vary among species.
Production of Enzymes by PGPR. In terms of PGPR producing protection enzymes, the mode of action could be labeled that of biopesticides: PGPR promote plant growth through the control of phytopathogenic agents, primarily for the production of metabolites contributing to the antibiosis and antifungal properties used as defense systems. The mechanism would involve the production of hydrolytic enzymes, of which two examples are chitinase and glucanase. Major fungal cell wall components are made up of chitin and beta-glucan, thus chitinases and beta-glucanases producing bacteria would inhibit fungal growth. The Sinorhizobium fredii KCC5 and Pseudomonas fluorescens LPK2 produce chitinase and beta-glucanases and dictate the fusarium wilt produced by Fusariumudum.
Opinion and comments
In my opinion, microbial farming is a really great technology or solution that we need to develop to solve our food security problem, and also to improve our ecosystem's health. However, the knowledge about microbe-plant interaction is still limited, and the application of microbes in the farming practice are still challenging and giving inconsistent results. When we could break this gap, then we could enhance overall human beings and ecosystems.
References
- Vejan, P., Abdullah, R., Khadiran, T., Ismail, S., & Nasrulhaq Boyce, A. (2016). Role of Plant Growth Promoting Rhizobacteria in Agricultural Sustainability-A Review. Molecules (Basel, Switzerland), 21(5), 573.
- Backer, R., Rokem, J. S., Ilangumaran, G., Lamont, J., Praslickova, D.,
Ricci, E., Subramanian, S., & Smith, D. L. (2018). Plant
Growth-Promoting Rhizobacteria: Context, Mechanisms of Action, and
Roadmap to Commercialization of Biostimulants for Sustainable
Agriculture. Frontiers in plant science, 9, 1473.
No comments:
Post a Comment