This document provides an overview of plant growth promoting rhizobacteria (PGPR). It begins with an introduction to PGPR and their potential as an alternative to pesticides in agriculture. It then covers the classification of PGPR into extracellular and intracellular types. The main mechanisms by which PGPR promote plant growth are discussed, including nitrogen fixation, phosphate solubilization, siderophore production, phytohormone production, and biocontrol activities. The roles of PGPR in agriculture as biofertilizers, biostimulants, and biopesticides are outlined. Future research directions are identified, such as developing multi-strain bacterial consortia. The conclusion emphasizes the multiple beneficial activities of PGPR for plant growth and

1. WELCOME

2. COLLEGE OF AGRICULTURE, BABHULGAON
TAL.:- YEOLA, DIST.:- NASHIK
Seminar on
PLANT GROWTH PROMOTING RHIZOBACTERIA
Submitted to
The Chairman
AEL PATH- 487
Guided by Submitted by
Dr. S.A.Raut Sir Chede Akshay Ashok
Head of Dept. AGB-2014/12
DEPARTMENT OF PLANT PATHOLOGY

3. PGPR
PLANT GROWTH PROMOTING RHIZOBACTERIA

4. CONTENTS
1. Introduction
2. What is PGPR
3. Classification of PGPR
4. Mechanism of action of PGPR
5. Role of PGPR in Agriculture
6. Importance of PGPR in Agriculture
7. Future research and development strategies
8. Conclusion

5. INTRODUCTION
• Biological control of plant pathogen has been the subject of much research in
recent years.
• It can potentially help us to reduce the use of pesticides that are harmful to the
environment.
• The use of PGPR (Plant Growth Promoting Rhizobacteria) such as siderophore
producing bacteria represents a potentially attractive alternative disease
management approach, since they have the capacity to increase the yield and
protect crop simultaneously.
• Few organisms like Pseudomonas putida,P. fluorescence has been widely used as
bio-control agent.

6. WHAT IS PGPR ?
• PGPR term was coined for the first time by Kloepper and Schroth (1981) to
describe this microbial population in the rhizosphere which is beneficial, colonize
the roots of plants and shows plant growth promotion activity.
• Concept of Rhizosphere was first given by Hiltner(1904) to detect the zone of
soil surrounding the roots where microbial populations are accelerated by root
activities.
• “PGPR are the bacteria that colonize plant roots and promote plant growth
and reduce insect or disease damage (Stuart Mcmillan, 2007)”.

7. CLASSIFICATION OF PGPR
1.Extracellular plant growth promoting rhizobacteria
(ePGPR)
2.Intracellular plant growth promoting rhizobacteria
(iPGPR)

8. EXTARCELLULAR PGPR
 The ePGPRs may exist in the rhizosphere, on the rhizoplane or in
the spaces between the cells of root cortex.
 The bacterial genera such as Agrobacterium, Azotobacter, Azospirillium,
Bacillus, Caulobacter, Cromobacterium, Erwinia, Microccous,etc.

9. INTRACELLULAR PGPR
 iPGPRs locates generally inside the specialized nodular structures of root
cells.
 iPGPRs belongs to the family of Rhizobiaceae includes Allorhizobium,
Bradyrhizobium, Frankia, Mesorhizobium,etc.

10. Mechanism of action of PGPR
Direct Plant Growth Promotion
(Biofertilizer Activity)
Indirect Plant Growth Promotion
(Biocontrol Activity)
1.Nitrogen Fixation
2.Phosphate Solubilization
3.Potassium Solubilization
4.Siderophore Production
5.Phytoharmone Production
a.IAA
b.Cytokinin, GA
c.Ethylene
1.Antibiotic Production
2.Hydrolytic Enzyme Production
3.Induced Systemic Resistance(ISR)
4.Exopolysaccharide Production

11. NITROGEN FIXATION
 The atmospheric nitrogen is converted into plant–utilizable forms by
biological nitrogen fixation (BNF) which changes nitrogen to ammonia by
nitrogen fixing microorganisms using a complex enzyme system known as
Nitrogenase.
 Nitrogenase complex enzyme carries nitrogen fixation which is two component
metalloenzyme consisting of Dinitrogenase reductase and Dinitrogenase.

12. NITROGEN FIXING MICROORGANISMS
1. Symbiotic Nitrogen Fixing Bacteria :-
e.g:-Rhizobacteria,
Frankia,

13. 2. Non-symbiotic :-
e.g.:- Blue Green Algae,
Azotobacter,

14. NODULATION PROCESS
a)Rhizobial attachment with root cells.
b)Excretion of nod factors by Rhizobia causes root hair curling.
c) Rhizobia penetrate root hair and form an infection thread through which they
penetrate cortical cells and form bacteroid state and thereby nodules are
formed.

15. PHOSPHATE SOLUBILIZATION
 Plants absorbs Phosphorus in only two soluble forms, the monobasic(HPO4ˉ)
and the dibasic(H2PO4ˉ).
 Phosphate solubilizing bacteria are considered as promising bio fertilizers since
they can supply plants with P from sources otherwise poorly available by various
mechanisms.
 Bacterial genera like Azotobacter, Bacillus, Beijerinckia, Erwinia,
Pseudomonas, Rhizobium and Serratia are reported as the most significant
phosphate solubilizing bacteria.

16. PSB

17. POTASSIUM SOLUBILIZATION
 More than 90% of potassium in the soil exist in the form of insoluble rocks and
silicate minerals.
 PGPR are through production and secretion of organic acids able to solubilize
potassium rock.
 Potassium solubilizing PGPR such Acidothiobacillus, Burkholderia and
Pseudomonas has been reported to release potassium in accessible form from
potassium bearing minerals in soils.
 Thus, application of potassium solubilizing PGPR as biofertilizer for agriculture
improve and support eco-friendly crop production.

18. SIDEROPHORE PRODUCTION
 Siderophore is a Greek word means Iron carrier.
 They are small high affinity iron chelating compound secreted by bacteria and
fungi.
 Kloeppar et al.(1980) were the first to demonstrate the importance of
siderophore.
 Plants are able to takeup the labelled iron by large no. of PGPR including
Azotobacter, Bacillus etc.

19. +-
Iron is often insoluble
(oxides and hydroxides)
Cells produce
siderophores
Iron binds to
siderophore complex
Iron is taken up by the
cell
Iron is reduced
(Fe3 into Fe2 )
Siderophore binds to
recognition sides on
cell
FORMATION OF SIDEROPHORE

20. PHYTOHARMONE PRODUCTION
 PGPR produce phytoharmone such as Auxins, Cytokinin, GA, and Ethylene
can affect proliferation in the root architecture.
1.INDOLE ACETIC ACID(IAA):-
It is the most common natural auxin found in plants and its
positive effect on root growth. Upto 80% of rhizobacteria can synthesize IAA.
IAA affect plant cell division, extension and differentiation.
e.g. Enterobacter cloacae

21. 2.Cytokinin and GA:-
Several PGPR such as Azotobacter sp. , Rhizobium sp. etc. can
produce cytokinin and GA.
3.Ethylene:-
• The high conc. of ethylene induces defoliation and other cellular processes
that may lead to reduced crop performance.
• The enzyme 1-aminocyclopropane-1 carboxylic acid (ACC) is a prerequisite
for ethylene production, catalyzed by ACC oxidase.

22. INDIRECT MECHANISM
ANTIBIOTICS :-
 The production of antibiotics is considered to be one of the most powerful and studied bio-
control mechanisms of PGPR against phytopathogens.
 A variety of antibiotics have been identified, including compounds such as phenazine,
tropolone.
 Some rhizobacteria are also capable of producing volatile compound known as hydrogen
cyanide(HCN) for bio-control of Black Root Rot of Tobacco.
 E.g.:- Pseudomonas, Bacillus
LYTIC ENZYMES :-
 PGPR strains can produce certain enzymes such as Chitinases, Lipases, Phosphotases,
Proteases etc.

23. INDUCED SYSTEMIC RESISTANCE (ISR)
 Non-pathogenic rhizobacteria have been shown to suppress disease by inducing
a resistance mechanism in the plant called “Induced Systemic Resistance” (ISR).
 ISR involves jasmonate and ethelyne signaling within the plant and these
harmones stimulate the host plant’s defense responses against a variety of plant
pathogens.
 Many individual bacterial components induce ISR such as
Lipopolysaccharides(LPS), Siderophore and volatile compounds like Acetoin
etc.

24. EXO POLYSACCHARIDE PRODUCTION
 Production of Exo polysaccharide (EPS) is generally important in biofilm
formation.
 Effective colonization of plant root’s by EPS microbes helps to hold the free
Phosphorous from the insoluble one in soils and circulates essential nutrients to
the plant for proper growth and development and protecting it from the attack of
foreign pathogens.
 Some PGPR producing EPS can also bind cations, including Na+ suggesting a
roll in mitigation of salinity stress by reducing the contain of Na+ available for
plant uptake.

25. ROLE OF PGPR IN AGRICULTURE
 PHYTOSTIMULATORS :-
• They are the phytoharmone which stimulate the growth of plant in absence of pathogen.
• Best example is hormone auxin.
• Some volatile substances like Acetoin and 2,3-butandiol are also responsible for significant
improvements in plant growth.
 ABIOTIC STRESS TOLERANCE :-
• Abiotic stresses are due to content of heavy metal in soil drought, nutrient deficiency,
salinity etc.
• PGPR improves the leaf water stress of plants under salinity and drought conditions.

26.  BIOFERTILIZERS:-
• Bio fertilizers are defined as preparations containing live cells or latent cells of efficient
strains of micro-organisms that help uptake of nutrients by their interactions in the
rhizosphere when applied through seed or soil.
• Sufficient densities of PGPR in biofertilizer provide a beneficial role creating a proper
rhizosphere for plant growth and converting nutritionally important elements through
biological process.
 BIOPESTICIDE:-
• PGPR strains produces certain enzymes such as Chitinase, Dehydrogenase, Lipases,
Proteases etc.
• Exhibit hyperparasitic activity, attacking pathogens by excreting call wall hydrolases.

27. IMPORTANCE OF PGPR IN AGRICULTURE
 Increased health and productivity of different plant species by the application
of PGPR under both normal and stressed conditions.
 The plant-beneficial rhizobacteria may decrease the global dependence on
hazardous agricultural chemicals which destabilize the agro-ecosystem.
 The rhizobacteria are dominant deriving forces in recycling the soil nutrients and
consequently, they are crucial for soil fertility.
 Novel traits like heavy metal detoxifying potentials, pesticide
degradation/tolerance.
 Salinity tolerance and biological control of phytopathogens and insects.

28. FUTURE RESEARCH AND DEVELOPMENT
STRATEGIES
 Future research in rhizosphere biology will rely on the development of
molecular and biotechnological approaches to increase our knowledge of
rhizosphere biology and to achieve and integrated management of soil
microbial populations.
 Fresh alternatives should be explored for the use of bio inoculants for other high
value crops such as vegetables, fruits, and flowers.
 The application of multi strain bacterial consortium over single inoculation
could be an effective approach for reducing the harmful impact of stress on
plant growth.

29. CONCLUSION
1. PGPR have a multiple of activities directed towards plant growth and
controlling pollutants and pesticides.
2. Their productive efficiency can be enhanced by improving soil conditions.
3. In future they might replace chemical fertilizers and pesticides which have
many bad effects on agriculture.
4. We might be able to find more competent rhizobacterial strains which may work
under several conditions.

30. Thank
you….