PGPR
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Plant growth promoting bacteria (PGPB) include rhizosphere and phyllosphere bacteria that can benefit plants. PGPB are classified as either rhizoplane bacteria that colonize roots, or intracellular bacteria that exist inside root cells. PGPB promote plant growth through various mechanisms including nitrogen fixation, siderophore production, phytohormone production, phosphate solubilization, induced systemic resistance, and antagonism against pathogens. While PGPB show potential for controlling plant diseases, their commercial use faces challenges in selection and characterization, field application, and commercialization due to natural variation, formulation and delivery issues, and high costs.
PGPR
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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 (i-PGPR, symbiotics) Exist inside root cells. Forms root nodules. Ex- Rhizobium Extracellular (e-PGPR, 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, MFD-4, 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)
- 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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