6. Introductionโฆ
What are PGPR
โข A group of Soil Born Bacteria (Rhizobacteria)
โข Actively colonize plant roots / Rhizosphere
โข Enhance plant Growth and Yield
โข Directly or Indirectly
- Introduced by JW Kloepper, MN Schroth (1978)
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9. Characteristics of PGPR
They must,
1) Able to colonize the root
2) Survive and multiply in microhabitats associated with the
root surface, in competition with other microbiota
3) Promote plant growth Or /and
4) Promote plant protection activities
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10. Types of PGPRs
1. Extracellular (ePGPR)
Existing in/on the
โข Rhizosphere
โข Rhizoplane
โข spaces between cells of
the root cortex
2. Intracellular (iPGPR )
โข Exist inside root cells
โข Generally in specialized
nodular structures.
Fig: Structure of nitrogen-fixing root nodules
-Marรณti and Kondorosi (2014)
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11. Functional classification of PGPR
a) Direct activity
Nutrient cycling
Phyto-stimulation
โข MO themselves release growth regulators
โข MO act as a sink of plant-released hormones
b) Indirect activity
Systemic resistance to Biotic Stress
Protection against Abiotic Stress
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14. 1. Biological Nitrogen fixation
๏ง Nitrogen is a vital nutrient for Plant
๏ง 78% N2 in the atmosphere
๏ง But not directly utilizable for plants
โข BNF fixes ~ 60% of the earth's
available Nitrogen
โข 20 - 30 kg per hectare per year
โข Biofertilizers
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15. 1. Biological Nitrogen fixationโฆ
a) Symbiotic
๏ง Specificity
๏ง Infect the roots to produce nodule
1) With leguminous host plants (e.g., rhizobia)
2) With non-leguminous trees (e.g., Frankia)
Fig3: Nodule formation of Frankia alni
Sourse:
http://bladmineerders.nl/wordpress/wp-
content/uploads/beeld/_752_2.jpg
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20. 2. Phosphate solubilization
๏ง Limiting nutrient for plants (due to insoluble forms)
๏ง Eg: Tricalcium phosphate, Rock phosphate, Aluminum
phosphate, etc.
๏ง Plants are only able to absorb mono- and dibasic
phosphate ( soluble forms )
)
๏ง (H2PO4
๏ง (HPO4)
๏ง PGPR mineralize organic / inorganic phosphorus in soil
๏ง Phosphate-solubilizing bacteria
2-
-
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21. 2. Phosphate solubilizationโฆ
Primary Mechanism
1) Organic acid secretion by microbes
๏ง utilize sugars from root exudates
๏ง produce organic acids
๏ง acetic, lactic, malic, succinic, tartaric, gluconic,
2-ketogluconic, oxalic and citric acids
๏ง act as good chelators of divalent Ca2+ cations
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22. 2. Phosphate solubilizationโฆ
Other Mechanisms
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2) Produce extra cellular enzyme
๏ง Phytase
Hexaphosphate salt of inositol (phytate)
๏ง Phosphatase
2) Release of Phosphate during substrate
dgredation
24. ๏ง Cause to substantial increase in growth and yield
of plants
๏ง Plant responds to any phytohormone in the
rhizosphere
๏ง Auxins
๏ง Gibberellins
๏ง Cytokinins
3. Phytohormone production
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25. 3. Phytohormone productionโฆ
1) Indole-3-acetic acid (IAA) โan auxin
๏ง cell elongation
๏ง cell division
๏ง tissue differentiation
๏ง aids apical dominance
โข Highly developed roots
โข Uptake more nutrients
~ 80% of the bacterial flora in the rhizosphere produce
IAA
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26. 3. Phytohormone IAA โฆ
Fig7: Biosynthesis pathways of
IAA in PGPR
Ahemad and Mohammad(2011)
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27. 2) Cytokinins
๏ง cell division
๏ง root development
๏ง root hair formation
๏ง shoot initiation
๏ง inhibition of root elongation
- Influence their physiological and developmental
processes
- Pseudomonas, Azospirillum, and Bacillus
3. Phytohormone productionโฆ
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28. 3. Phytohormone Cytokinins โฆ
๏ง Most abundant cytokinins are
Adenine-type
๏ง Two different pathways
1) the tRNA pathway
2) adenosine monophosphate
(AMP) pathway
Fig8: Zeatin Biosynthesis pathway studied in Paenibacillus polymyxa OSY-DF.
Ahemad and Mohammad(2011)
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29. 3) Gibberellins (GAs)
๏ง Seed germination
๏ง Stem elongation
๏ง Flowering & fruit setting
- 136 GA s are known from plants .
- Only 4 from PGPR - GA1, GA3, GA4, and GA20
- Effect of PGPR producing GAs on plant is not exactly
known
- But used in the seed germination
- B. Pumilus , B. licheniformis
3. Phytohormone productionโฆ
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31. ๏ง Iron is an essential nutrient
๏ง Quite abundant, but unavailable for plants & MO
๏ง Insoluble oxides and hydroxides inaccessible
๏ง Siderophoresโ functional groups capable of
binding iron in a reversible way
๏ง Rhizosphere bacteria release these compounds to
increase their competitive potential
1. Siderophore production
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32. โข Release iron-chelating molecules to the rhizosphere
โข Improve iron nutrition - attract iron towards the
rhizosphere
โข Inhibit the growth of other micro-organisms
โข Hinder the growth of pathogens by limiting
the iron available for the pathogen (Fungi)
PGPR
Pseudomonas fluorescens & Pseudomonas aeruginosa
1. Siderophore productionโฆ
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34. ๏ง Control soil borne pathogens (biocontrol agents)
๏ง Production of cell wall-degrading enzymes
โข ร-1,3-glucanase
โข Chitinase
โข Cellulase
โข Protease
๏ง Direct inhibitory effect on the hyphal growth of
fungal pathogens
2. Chitinase & glucanase production
Chitinase
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35. ๏ง Microbial antagonists against plant pathogens
๏ง Alternate to chemical pesticides
๏ง Bacillus and Pseudomonas species
๏ง Inhibitory even at low concentrations
Bacillus subtilis 168
antibacterial and antifungal antibiotics
3. Antibiotic production
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36. ๏ง Protect plant from diseases,
- Via induced systematic resistance (ISR)
๏ง Increase in the level of basal resistance to several
pathogens simultaneously
๏ง Pseudomonas strains
๏ง A signal is generated involving jasmonate or
ethylene pathway
๏ง Thus inducing the host plantโs defense response.
4. Induced systematic resistance
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45. Conclusion
๏ง Essential for Sustainable agriculture
๏ง Many identified not been commercialized
efficiently
๏ง Should do further research on detailed
understanding of their mechanics
๏ง A lot of effort is still required to make PGPR, an
efficient technique in sustainable agriculture
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47. REFERENCES
โข Ahemad, M. and Khan, M.S., 2011. Functional aspects of plant growth
promoting rhizobacteria: recent advancements. Insight Microbiol, 1(3), pp.39-
54.
โข Gopalakrishnan, S., Sathya, A., Vijayabharathi, R., Varshney, R.K., Gowda, C.L.
and Krishnamurthy, L., 2015. Plant growth promoting rhizobia: challenges and
opportunities. 3 Biotech, 5(4), pp.355-377.
โข Goswami, D., Thakker, J.N. and Dhandhukia, P.C., 2016. Portraying mechanics of
plant growth promoting rhizobacteria (PGPR): A review. Cogent Food &
Agriculture, 2(1), p.1127500.
โข Kumar, A., Prakash, A. and Johri, B.N., 2011. Bacillus as PGPR in crop ecosystem.
In Bacteria in agrobiology: crop ecosystems (pp. 37-59). Springer, Berlin,
Heidelberg.
โข Kundan, R., Pant, G., Jadon, N. and Agrawal, P.K., 2015. Plant growth promoting
rhizobacteria: mechanism and current prospective. J Fertil Pestic, 6(2), p.9.
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48. REFERENCES
โข Mishra, J., Prakash, J. and Arora, N.K., 2016. Role of Beneficial Soil Microbes in
Sustainable Agriculture and Environmental Management. Climate Change and
Environmental Sustainability, 4(2), pp.137-149.
โข Noumavo, P.A., Agbodjato, N.A., Baba-Moussa, F., Adjanohoun, A. and Baba-
Moussa, L., 2016. Plant growth promoting rhizobacteria: Beneficial effects for
healthy and sustainable agriculture. African Journal of Biotechnology, 15(27),
pp.1452-1463.
โข Richardson, A.E., Barea, J.M., McNeill, A.M. and Prigent-Combaret, C., 2009.
Acquisition of phosphorus and nitrogen in the rhizosphere and plant growth
promotion by microorganisms. Plant and soil, 321(1-2), pp.305-339.
โข Vejan, P., Abdullah, R., Khadiran, T., Ismail, S. and Nasrulhaq Boyce, A., 2016.
Role of plant growth promoting rhizobacteria in agricultural sustainabilityโa
review. Molecules, 21(5), p.573.
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49. REFERENCES
โข Vacheron, J., Desbrosses, G., Bouffaud, M.L., Touraine, B., Moรซnne-Loccoz, Y.,
Muller, D., Legendre, L., Wisniewski-Dyรฉ, F. and Prigent-Combaret, C., 2013.
Plant growth-promoting rhizobacteria and root system functioning. Frontiers in
plant science, 4, p.356.
โข Yang, J., Kloepper, J.W. and Ryu, C.M., 2009. Rhizosphere bacteria help plants
tolerate abiotic stress. Trends in plant science, 14(1), pp.1-4.
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