The document discusses plant growth promoting rhizobacteria (PGPR) and their mechanisms and functions in promoting plant growth. It describes how PGPR can directly promote plant growth through mechanisms like nitrogen fixation, phosphate solubilization, siderophore production and phytohormone production. PGPR also indirectly promote growth by inhibiting pathogens through producing antibiotics, lytic enzymes and inducing systemic resistance in plants. Future research areas discussed include developing PGPR consortium, improving stress tolerance and making PGPR products more cost effective and environmentally friendly.

1. 12/27/2016
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2. RAWE (0+4)
SPEAKER
NEHA TANDON
INSTRUCTOR
MR. ACHIN KUMAR
ASST. PROF SSC
IAS,RGSC, BHU
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3. CONTENT
1. INTRODUCTION
2. RHIZOSPHERE AND PLANT GROWTH PROMOTING RHIZOBACTERIA
3. PGPR FORMS
4. PGPR MECHANISMS
a. DIRECT
b. INDIRECT
5. FUNCTIONS OF PGPR
a. BIOCONTROL PROPERTIES
b. BIOINOCULANT
c. ABIOTIC STRESS RESISTANCE
d. CO-INOCULATION
6. HARMFUL ASPECTS OF PGPR
7. FUTURE PROSPECTS
8. CONCLUSION
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4. INTRODUCTION
 Indiscriminate use of chemical fertilizers adversely
affects soil microorganism, fertility status of soil
and environment
 So, PGPRs are replacing agrochemicals for the
plant growth promotion
 Economically, environmentally beneficial for lower
production cost and for sustainable agriculture
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5. RHIZOSPHERE AND PLANT GROWTH
PROMOTING RHIZOBACTERIA
 Term rhizosphere given by Hiltner (1904) and term PGPR given
by Kloepper and Schroth (1981)
 Rhizosphere is the narrow zone of soil specifically influenced by
the root system
 Populated by microorganisms and the bacteria called
rhizobacteria
 Three types: beneficial, deleterious & neutral groups
 Beneficial free-living soil bacteria referred to as PGPR
 Bacillus and Pseudomonas spp. are predominant among PGPR
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6. PLANT GROWTH PROMOTING
RHIZOBACTERIAL FORMS
1. EXTRACELLULAR PGPR (ePGPR)
 In rhizosphere, rhizoplane or between cells of root cortex
 Includes Agrobacterium, Arthrobacter, Azotobacter, Azospirillum, Bacillus,
Caulobacter, Chromobacterium, Erwinia, Flavobacterium, Micrococcous,
Pseudomonas and Serratia
2. INTRACELLULAR PGPR (iPGPR)
 Inside specialized nodular structures of root cells.
 Includes Allorhizobium, Bradyrhizobium ,
Mesorhizobium and Rhizobium, endophytes and Frankia
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7. PGPR MECHANISMS
1.DIRECT MECHANISM
 Providing plant with a compound synthesized by bacterium or
facilitating uptake of nutrients from the environment
2. INDIRECT MECHANISM
 Reducing or preventing deleterious effects of phytopathogenic
organisms by producing antagonistic substances or by inducing
resistance
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8. Fig : The possible mode of action used by PGPR towards growth promotion in plants. The flow and
location of nitrogen fixation, phosphorus solubilization, and siderophore production are shown
(Vacheron, Desbrosses, Bouffaud, Touraine.,2013)
MODE OF ACTION OF PGPR
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9. DIRECT MECHANISMS
 Two mechanisms:-
a. SYMBIOTIC NITROGEN FIXATION
 Mutualistic relationship between a microbe and the plant.
 Eg. Rhizobium, Bradyrhizobium, Sinorhizobium, Mesorhizobium and Frankia
b. NON-SYMBIOTIC NITROGEN FIXATION
 By free living diazotrophs
 Eg. Azotobacter, Acetobacter, Azospirillum,, Diazotrophicus, Enterobacter,
Pseudomonas and cyanobacteria
 Provides an integrated approach for disease management and maintains
nitrogen level in soil.
1. NITROGEN FIXATION
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10.  The main P solubilization mechanism includes:
a. Release of complex or mineral dissolving compounds
b. Liberation of extracellular enzymes
c. Release of P during substrate degradation
 Includes genera Arthrobacter, Bacillus, Beijerinckia,
Enterobacter, Erwinia, Flavobacterium, Microbacterium
Pseudomonas, Rhizobium, Rhodococcus, and Serratia
2. PHOSPHATE
SOLUBILIZATION
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11. MOVEMENT OF PHOSPHORUS IN SOIL
Source: Insight Microbiology;volume 1;issue 3, 20112/27/2016
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12. P SOLUBILIZATION BY P SOLUBILIZING BACTERIA
Source: Insight Microbiology;volume 1;issue 3,
201112/27/2016 12

13.  K is the third major essential macronutrient
 PGPR solubilize K rock through production and
secretion of organic acids.
 They release K in accessible form from K bearing
minerals in soils
 Includes genera Acidothiobacillus ferrooxidans,
Bacillus edaphicus, Bacillus mucilaginosus,
Burkholderia, Paenibacillus sp. and Pseudomonas
3. POTASSIUM
SOLUBILIZATION
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14.  Siderophores are low molecular weight iron-
chelating compounds which provide a high affinity
to coordinate ferric ions.
 Kloeppar et al. (1980) were the first to demonstrate
the importance of siderophore.
 Direct benefit: Take up the labeled iron and
chelating scarcely available iron
 Indirect benefit: Enhanced chlorophyll level
4. SIDEROPHORE
PRODUCTION
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15. IMPACT OF MICROBIALLY SECRETED SIDEROPHORES ON PLANT GROWTH
Source: Insight Microbiology;volume 1;issue 3,
2011
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16. a. Indole Acetic Acid (IAA)
 Up to 80% of rhizobacteria can synthesize IAA
 IAA stimulate cell proliferation, seed germination,
resistance to stressful conditions and enhance uptake of
minerals and nutrients
 Pseudomonas, Rhizobium, Bradyrhizobium,
Agrobacterium, Enterobacter and Klebsiella are IAA-
producing PGPR
5. PHYTOHORMONE
PRODUCTION
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17.  Includes genera Azotobacter sp., Rhizobium sp.,
Rhodospirillum rubrum, Pseudomonas fluorescens,
Bacillus subtilis etc
 Some strains of phytopathogens also synthesize cytokinins
 PGPR produce lower cytokinin levels compared to
phytopathogens
 Thus, effect of PGPR on plant growth is stimulatory while
that of pathogens is inhibitory.
b. Cytokinin and Gibberellins
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18.  Lowering of ethylene production by inoculation of PGPR strains
induces:-
1. Improved nodule number
2. Improved nodule dry weight
3. Higher grain yield and straw yield
4. Increased nitrogen
 Includes genera: Pseudomonas sp., Achromobacter, Agrobacterium,
Azospirillum, Bacillus, Burkholderia, Enterobacter, Ralstonia, Serratia
and Rhizobium etc.
c. Ethylene
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19. INDIRECT MECHANISMS
 One of the most powerful bio control mechanisms
 Antibiotics produced:-
 By psuedomonads: amphisin, (DAPG), oomycin A, phenazine,
tensin,, and cyclic lipopeptides
 By Bacillus, Streptomyces and Stenotrophomonas sp: oligomycin A
and xanthobaccin
 Drawback: some phytopathogens may develop resistance to
specific antibiotics due to increased use.
1. ANTIBIOTICS
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20.  PGPRs produce enzymes such as chitinases,
dehydrogenase, β-glucanase, lipases, phosphatases,
proteases etc. exhibiting hyperparasitic activity
 Suppression of pathogenic fungi including Botrytis
cinerea, Sclerotium rolfsii, Fusarium oxysporum,
Phytophthora sp., Rhizoctonia solani, and Pythium
ultimum
2. LYTIC ENZYMES
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21. 3. INDUCED AND SYSTEMIC
RESISTANCE
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22.  Functions of EP-producing PGPR:-
a. Biofilm formation and root colonization.
b. Holding free phosphorous
c. Circulating essential nutrient to the plant
d. Protecting from foreign pathogens and stress
e. Shielding from desiccation
f. Plant defense response in plant–microbe interactions
4. EXO POLYSACCHARIDE PRODUCTION
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23. BIOCONTROL PROPERTIES OF
PGPRS
 Bio control: Process through which a living organism limits the growth or
propagation of undesired organisms or pathogens
 Mechanism:-
a. Competition for nutrients
b. Production of antibiotics
c. Production of enzymes to degrade cell wall
d. Production of siderophores
e. Production of metabolites
f. Displacing pathogens
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24. APPLICATION OF PGPR AS
BIOINOCULANT
 Bio-fertilizers are defined as “substances that contain living microorganisms that
when applied to seed, plant surfaces, or soil, colonize the plant and promote its
growth by increasing the nutrient availability”
 Mechanism:-
a. Increase efficiency of N-fixation
b. Ability to solubilize phosphate
c. Improve availability of Fe and Zn
d. Alter growth of roots and shoots by phytohormones
 Eg: strains of Pseudomonas putida & Pseudomonas fluorescens
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25. ABIOTIC STRESS RESISTANCE THROUGH
PGPR
 High temperatures lead to increased drought
intensity; reduction in nodule number; infectious
events; delay in nodulation
 Heat-tolerant, actively nodulating and
N2 fixing Rhizobium strains identified that play a
key role in normal growth.
1. EXTREME
TEMPERATURES
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26.  Soil acidity affects plant growth and cause crop
failures
 Some strains of Rhizobium,
Azorhizobium and Bradyrhizobium are low pH
tolerant.
 Tolerance to acidity by rhizobia correlated with the
production of extracellular polysaccharide
2. SOIL ACIDITY
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27.  Key pollutants to plants, ecosystem and humans.
 Use of recombinant rhizobia plays a major role in
phyto-remediation measures.
 Microorganisms with high metal-binding capacity
through metallothionins for enhancing the
tolerance, sequestration of heavy metals widely
exploited.
3. HEAVY METAL RESISTANCE
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28. SYNERGISTIC EFFECTS OF RHIZOBIAL CO-
INOCULATION
 Inconsistency of beneficial results, when single microbe used
 Co-inoculation causes synergy by functioning as helper bacteria
 Best combination of PGP bacteria, rhizobia and host genotype
selected
 Examples:-
a. Azospirillum: In leguminous crops
b. A. lipoferum and R. leguminosarum pv. trifolii : White clovers
c. Azotobacter
d. Bacillus sp.
e. Psuedomonas sp.
f. Enterobacter
g. Serratia
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29. HARMFUL ASPECTS OF PGPR
 Cyanide acts as a growth inhibitor for some plants
 High levels of auxin inhibits root growth
 Rhizobitoxine produced by Bradyrhizobium elkanii
may have a negative effect on nodulation
 Rhizobitoxine can also induce foliar chlorosis in
soybeans.
 A select few bacterial species may inhibit growth.
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31. FUTURE RESEARCH AND DEVELOPMENT
STRATEGIES
 Need of today’s world – higher yield and enhanced production in an eco-friendly manner
1. New concepts of rhizo-engineering
2. Research in rhizosphere biology (molecular & biotechnological approaches)
3. Integrated management of soil microbial populations
4. Bioinoculants for high value crops like vegetables, fruits, and flowers
5. Application of multi strain bacterial consortium over single inoculation
6. Addition of ice-nucleating plant growth promoting rhizobacteria
7. Comprehensive research on potassium solubilization
8. Biosafety data required for the registration of PGPR
9. Non-phytotoxic PGPR
10. PGPRs tolerant to adverse environmental condition
11. Cost effective PGPR products
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32. CONCLUSION
 PGPRs are economically and environmentally beneficial for
plant growth promotion
 PGPRs may have a direct or an indirect mode of action
 PGPRs may function as biofertilizer, bioinoculant, abiotic
stress resistance inducers, co-inoculants and other growth
promoting activities
 New concepts and development strategies regarding PGPRs
need to be constantly developed
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33. THANK YOU
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