includes rhizoplane bact and phylloplane bact -whole mechanism

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2. Plant growth promoting
bacteria and their role in
disease management

3. INTRODUCTION
• PGPB includes Rhizoplane and Phylloplane bacteria.
Rhizoplane Bacteria:
• “Plant Growth Promoting Rhizobacteria”(PGPR).
• Term PGPR was first used by Joseph W. Kloepper
and Schroth in the late 1970s.
• PGPR are root colonizing (rhizosphere) bacteria
benificial to plants.
• Rhizosphere is the region around roots having high
microbial activity.

4. • Term Rhizosphere was
coined by German
agronomist Hiltner in
1904.
• Rhizoplane
The external surface of
roots together with closely
adhering soil particles and
debris.

5. DIVERSITY AMONG PGPRS
Diazotrophic PGPR
 Nitrogen Fixation is one of the most beneficial
processes performed by rhizobacteria.
 Rhizobacteria converts gaseous nitrogen (N2) to
ammonia (NH3) making it available to the host plant.
 Nitrogenase enzyme is involved in nitrogen fixation
and requires anaerobic conditions.
 Ex- Azospirillum, Bradyrhizobium, Rhizobium,
Serratia, Enterobacter , Burkholderia spp.

6. Bacillus
 95% of Gram +ve soil bacilli belong to the genus
Bacillus.
 The remaining 5% are confirmed to be Arthrobacter
and Frankia.
 Members form endospores to survive under
adverse conditions.
Pseudomonas
 Pseudomonas is the most abundant gram –ve genus
in rhizosphere.
 The ecological diversity of this genus is enormous.

7. • Pseudomonas strains show high
versatility in their metabolic activity.
• Antibiotics, siderophores, HCN are
the metabolites released by these
strains.

8. Taxonomy of PGPB
 Earlier bacterial taxonomy relied on phenotypic
traits like cell and colony morphologies.
 Taxonomy revolutionized with the discovery of PCR
technique in 1983.
 The gene sequences of 16S subunit of rRNA are
used to compare similarities among strains.
 Nowadays characteristics of strains are studied
using FAME technique, Protein estimation by SDSPAGE technique and MLEE.

9. Classification of PGPR
On the basis of
1. Plant part they occupy
Intracellular (iPGPR, symbiotics)
Exist inside root cells.
Forms root nodules.
Ex- Rhizobium
Extracellular (ePGPR, free living
Exist in rhizosphere,on
rhizoplane, in intercellular
spaces of root cortex.

12. Siderophore Production
• Siderophores are high-affinity iron chelating
compounds secreted by microorganisms.
• Siderophores chelate ferric ion with high
affinity, allowing its solubilization and extraction
from most mineral or organic complexes.
• Bacterial siderophores classified into four main
classes carboxylate, hydroxamates, phenol
catecholates and pyoverdines.

13. s
Siderophore
Bacillibactin
Ornibactin
Azotobactin
Pyoverdine
Organism
pathogen
Bacillus subtilis
Burkholderia cepacia
Azotobacter vinelandii
Pseudomonas aeruginosa

14. Microbial Antagonism
 Achieved through bacteriocins, antibiotics
hydrolytic enzymes,HCN production, SAR, ISR.
Antibiotics
 PGPR produces
antibiotics and act as
antagonistic.
 Biocontrol based on
Pathogen
antibiosis secretion of
molecules that kill
target pathogen
Antibiosis
ISR
Competition

15. Sr. Antibiotic
No
Source
Action against
1.
Pyrrolnitrin
P. Fluorescens
BL915 strain
Prevent the damage
of Rhizoctonia solani during
damping-off of cotton plants
2.
DAPG
Pseudomonas
spp.
Membrane damage
to Pythium spp.
3.
Phenazine
Pseudomonas
spp.
F. oxysporum,
Gaeumannomyces graminis
4.
Polymyxin,
circulin and
colistin
Bacillus spp.
Pathogenic fungi
5.
Zwittermicin A B. cereus UW85 Bio-control of alfalfa damping
strain
off

16. Production of Phytohormones
• Phytohormone production by PGPR was first
reported in 1940.
• Auxin and Ethylene are more commonly produced
hormone, Cytokinin is less common.
• Auxin promotes lateral root formation, cell division,
apical dominance etc.
• Among PGPR species, Azospirillum is one of the best
studied IAA producers (Dobbelaere et al., 1999)

17. ROOTS WITHOUT PGPR
ROOTS WITH PGPR
• Production of Gibberellins by PGPR is rare,
• However two strains have been reported, Bacillus
pumilis and Bacillus licheniformis.

18. Bacteriocin
Sr.No
Bacteriocin
PGPR
1.
2.
3.
4.
Pyocins
Cloacins
Marcescins
Megacins
P. pyogenes
Enterobacter cloacae
Serratia marcescens
B. megaterium
HCN producing rhizobacteria
• HCN is a powerful inhibitor of metal enzymes, especially
cytochrome C oxidases.
• HCN production is a common trait within the group
of Pseudomonas.
• Include species
of Alcaligenes, Bacillus, Pseudomonas and Rhizobium.

19. • Strawberry fruits were harvested and transported
to the laboratory.
• Dipped in a suspension of B. cinerea conidia and
allowed to dry for 1 h.
• Then inoculated with bacterial suspensions.
• Control fruits dipped in conidia, dried and dipped in
nutrient broth diluted with sterile distilled water,
• Fruits were incubated for 4 days at 25°C, and then
observation was recorded.
Donmez et al., 2011

20. Cont..
Donmez et al., 2011

21. Result:
• No significant differences between CD-8, MFD4, MFD-18, MFDÜ-1 and control
• Highest percentage of gray mold infection (79.2%)
was observed in the control and
• Lowest (20.8%) was in MFD-45, followed by MFD81 (25.0%) and T26 (37.5%).
Conclusion:
PGPB were effective in biocontrol of Botrytis
cinerea on strawberry fruit.

22. Fixation of Atmospheric N2
• There are two types of biological fixation:
symbiotic and non-symbiotic.
• The first is the most important mechanism by which
most atmospheric N is fixed.
• It is limited to legume plant species and various trees
and shrubs that form actinorrhizal roots
with Frankia.
• Non-symbiotic N-fixing rhizospheric bacteria belongs
to genera including
Azoarcus, Azospirillum, and Pseudomonas

23. Most studied symbiotic bacteria
are Rhizobium, Bradyrhizobium, Sinorhizobium and
Mesorhizobium

24. Induced Systemic Resistance
• PGPR interact with plant in a restricted area but
response is extended to whole plant.
• Salicylic acid, which plays a protective role in
acquired systemic resistance .
• While acquired systemic resistance is induced upon
pathogen infection, induced systemic resistance can
be stimulated by other agents, such as PGPB
inoculants.
• Plants inoculated with the biocontrol PGPB, P.
putida and Serratia marcescens were protected
against the cucumber pathogen P. syringae pv.
lachrymans.
Bashan &Bashan., (2005)

25. Induced Systemic Resistance

26. Role of siderophore in induction of SAR
• E. chrysanthemi produces two
siderophores
Achromobactin ( iron limiting
condition)
Chrysobactin (severe iron
deficiency)
The role of CB in induction of
SAR has been studied in
Arabidopsis- Erwinia
chrysanthemi system.

27. Cont.
Fig: PR1 gene expression and SA production in Arabidopsis leaves
following CB treatment (Dellagi et al., 2009).

28. Production of Enzymes
• Hydrolytic enzymes produced by some biocontrol PGPB
lyse specifically fungal cell walls, and thereby prevent
phytopathogens from proliferating .
• Ex. Pseudomonas stutzeri produces chitinase that lyse
cell wall of Fusarium solani.
• Another strategy is the hydrolysis of fungal products
harmful to the plant.
• Ex.Cladosporium werneckii and B. cepacia can hydrolyze
fusaric acid that causes severe damage to plants.
(Hillel, 2005)

29. 1
1
1
1
1
4
Lim et al., 1991

30. Cont..
Lim et al., 1991

31. Cont..

32. Competition and Displacement of
Pathogens
• Competition for nutrients and suitable niches
among pathogens and is another mechanism of
biocontrol of some plant diseases.
• Ex- high inoculum level of Pseudomonas syringae
protected pears against Botrytis cinerea and
Penicillium expansum .
• Bacteria capable of multiplying on the leaf surface
to form a large population can compete successfully
with pathogens for these sites and often reduce
disease.

33. List of PGPRs
PGPR
Disease promoting
traits
References
Pseudomonas
fluorescens
IAA, HCN
Jeon et al. (2003)
Pseudomonas
fluorescens
IAA, Siderophore,
Antifungal activity
Dey et al. (2004)
Bacillus subtilis
Antifungal activity
Cazorla et al. (2007)
Bradyrhizobium spp.
IAA,Siderophore, HCN
Wani et al. (2007a)
Pseudomonas, Bacillus
, IAA and Siderophores
Wani et al. (2007e)
Azospirillum
amazonense
IAA, Nitrogenase activity
Elisete et al. (2008)
Rhizobium
leguminosarum
IAA, Siderophores, HCN,
Exopolysaccharides
Ahemad and Khan
(2009a)

34. PHYLLOPLANE BACTERIA
• Defined as populations that can
survive and multiply on the surface of
plants.
• Also called as epiphytic bacteria.
• survive in trichomes
base, substomatal
chambers, hydathodes, and
especially, in between the depressions
along the junctions of adjacent
epithelial cells.
• They utilize similar mechanism for
controlling of pathogens like
antibiosis, siderophore production etc.

35. Location of the epiphytotic PGPB in tomato
P. macerans
P. macerans
B. pumilus
B. pumilus
control
control

36. Bacterial spot and early blight biocontrol by
epiphytotic bacteria in tomato plants
Filho et al., 2010

37. Cont…
Filho et al., 2010

38. Conclusion
(I) Paenibacillus macerans and Bacillus pumilus
epiphytic bacteria and benzalkonium chloride reduce
Xanthomonas vesicatoria and Alternaria solani disease
severity in tomato plants.
(II) Epiphytic bacteria are able to inhibit the growth of
tested phytopathogens, and efficiently
colonize the phylloplane of tomato plants.

39. Challenges
with PGPB
Challenges in
Selection and
Characterization
of PGPB
Natural
variation
Challenges in
Field
Application of
PGPB
Challenges in
Commercialization
of PGPB

40. Challenges in Selection and
Characterization of PGPB
• Lack of proper selection and screening procedure
thus most promising organisms aren’t identified.
• Effective strategies for initial selection and
screening of PGPB isolates are required.
• Selection of PGPB with the potential to control soilborne pathogens
• Selection based on traits known to be associated
with PGPB such as root colonization, ACC
deaminase activity, antibiotic and siderophore
production.

41. Con…
Natural variation
 Prediction how an organism will respond
when placed in the field (compared to the
controlled environment of a laboratory.
 lack of consistency and many variation in
results that are obtained in field trials
 PGPB bacteria will not live forever in a
soil/leaves, there is need to re-inoculate
seeds to bring back populations.

42. Challenges in Field Application
of PGPB
CHALLENGE
• Lack
of
consistent
performance in the field
due to heterogeneity of
abiotic and biotic factors.
KNOWLEDGE
MANAGEMENT
REMEDY
• Knowledge of factors
optimal
concentration, timing and
placement
of
inoculant, and of soil and
crop
management
strategies
• concept of managing the
rhizosphere/phyllosphere
by manipulation of the
host plant, substrates for
PGPB,
or
through
agronomic practices.

43. Cont…
CHALLENGE
Lack
of
better
formulations
to
ensure survival and
activity in the field
• REMEDY
Approaches
include
development
of
improved carriers and
application technology

44. •
•
•
•
Challenges in Commercialization of PGPB
Maintaining quality, stability, and efficacy of
the product.
Factors like shelf life, compatibility
considered while formulation development.
Non-target effects on other organisms
including toxigenicity, allergenicity,
pathogenicity.
Capitalization costs and potential markets
must be considered in the decision to
commercialize.

45. CONCLUSION
• PGPB has dual role as plant growth
promotion and as bioagent.
• They control the plant pathogen in
direct as well as indirect way.
• PGPB is available in nature but their
screening is not easy.
• It is included in IDM strategy for
controlling several plant pathogens.

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