My recent lecture on Biological control of plant pathogens. It was a lecture presented in introductory to plant pathology undergraduate class.

1. RUFUS AKINRINLOLA
Graduate Student
Plant Pathology Department.
University of Nebraska-Lincoln
BIOLOGICAL CONTROL OF
PLANT PATHOGENS
BIOS/PLPT 369

2. Topics
1. Biological control
2. Importance of biological control
3. Mode of actions of biocontrol
4. Biocontrol application methods
5. Requirements for successful biocontrol agents
6. Limitations of biological control
7. Some commercial biological control agents
8. Summary
BIOLOGICAL CONTROL OF PLANT PATHOGENS

3. The term biological control :- as defined by Plant Pathologist;
 the use of microbial antagonists (including bacteria or fungi) to suppress
plant disease pathogens
BIOLOGICAL CONTROL
Inhibition of test organisms by biocontrol organism Sources: google image

4.  Alternative method of disease control
 Can be used in where other methods are not applicable.
 Biocontrol agents are nontoxic to man and the environment.
 Act on selective target organism.
 Biocontrol agents are self-sustaining-easy adaptation
 Diversify mode of actions
 Reduced possibility of inducing resistance in pathogens
 Cost effective
 Long term effects
Importance of biological control
Emmert, E. A., & Handelsman, J. (1999). Biocontrol of plant disease: a (Gram‐) positive perspective. FEMS Microbiology letters, 171(1), 1-9.

5. Mode of actions of biocontrol
1. Direct mechanism: Direct lysis or killing of pathogen by biocontrol agent
 Antibiosis
 Parasitism
Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58.
2. Indirect mechanism: Exclusion of plant pathogen as a result of the presence, activity
or products of biocontrol agent.
 Competition
 Induced systemic resistance

6. Mode of actions of biocontrol
1. Direct mechanism: Direct lysis or killing of pathogen by biocontrol agent
 Antibiosis
 Parasitism
Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58.
2. Indirect mechanism: Exclusion of plant pathogen as a result of the presence, activity
or products of biocontrol agent.
 Competition
 Induced systemic resistance

7. Mode of actions of biocontrol
1. Antibiotic mediated suppression
 Antibiotics are microbial toxins that can, at low concentrations, poison or kill other
microorganisms.
Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58.

8. Mode of actions of biocontrol
1. Antibiotic mediated suppression
 Antibiotics are microbial toxins that can, at low concentrations, poison or kill other
microorganisms.
Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58.
Inhibition of pathogens by biocontrol bacteria. Photo credit: Rufus Akinrinlola

9. Mode of actions of biocontrol
1. Antibiotic mediated suppression
 Antibiotics are microbial toxins that can, at low concentrations, poison or kill other
microorganisms.
 Volatile antibiotics
• Hydrogen cyanide,
• Aldehydes
• Alcohols
• Ketones
• Sulfides
 Nonvolatile antibiotics:
• Polyketides (diacetylphloroglucinol; DAPG and
mupirocin).
• Heterocyclic nitrogenous compounds.
Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58.

10. Mode of actions of biocontrol
Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58.
2. Parasitism
 Direct utilization of pathogens as source nutrients.
 Mycoparasitism refers to association in which a parasitic fungus (hyperparasite) live as a
parasite to another fungus (hypoparasiste).
 Also known as Hyperparasitism, when hyperparasites (biocontrol fungi) utilize
hypoparasites (pathogenic fungi) as source of nutrients.
 Hyperparasites produce parasitizing hyphae to acquire host nutrients.
 May also requires cell wall degrading enzymes.
Source: The Microbial World.

11. Mode of actions of biocontrol
Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58.
A B
Source: The Microbial
World.
Example of Mycoparasitism: Pythium oligandrum Vs Fusarium culmorum
A. Single hypha of Pythium
oligandrum stopped the advancement
of Fusarium culmorum hyphae across
an agar plate.
B. At higher magnification F. culmorum
hyphae are seen disrupted - the contents
are highly vacuolated and coagulated.

12. Mode of actions of biocontrol
Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58.
Steps involved in Mycoparasitism
1. Chemotropic growth: the biocontrol fungi grow toward the target fungi chemical
stimuli.
2. Recognition stage: interaction between biocontrol receptors and that of the host fungus
3. Attachment and cell wall degradation (chitinases and glucanases).
4. Penetration (appressoria-like structures).

13. Mode of actions of biocontrol
Ahanger et al., 2014; Dubey and Dwivedi, 1986.
Steps involved in Mycoparasitism
1. Chemotropic growth: the biocontrol fungi grow toward the target fungi chemical stimuli.
2. Recognition stage: interaction between biocontrol receptors and that of the host fungus
3. Attachment and cell wall degradation (chitinases and glucanases).
4. Penetration (appressoria-like structures).
Coiling Penetration
Barrier formation
by host hypha
Branching and
sporulation
Chlamydospores
formation
Lysis of
host hypha
Hyperparasite
(bicontrol)
Host fungus (pathogen)
hypha
Source: biocylopedia.com

14. Mode of actions of biocontrol
Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58.
Source: Koutb and Ali, 2010
3. Competition
 Exclusion of pathogens by biological control agents via competition for space or
nutrients.
 Production of substances (such as siderophore) for nutrient (such as iron) acquisition.
 Deprive pathogens of nutrients.
 It’s an indirect mechanism

15. Mode of actions of biocontrol
Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58.
Source: Koutb and Ali, 2010
3. Competition
 Exclusion of pathogens by biological control
agents via competition for space or
nutrients.
 Production of substances (such as siderophore)
for nutrient (such as iron) acquisition.
 Deprive pathogens of nutrients.
 It’s an indirect mechanism
Competition for space and nutrients between Pythium
irregulare pathogen (white restricted growth) and the
Epicoccum purpurascens (reddish wide growth) on
PDA medium after

16. Mode of actions of biocontrol
Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58.
4. Induced systemic resistance (ISR):
Also known as systemic acquired resistance (SAR), resistance in plants to
varieties of pathogens induced by the presence or products of biocontrol
agent.

17. Mode of actions of biocontrol
Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58.
ISR biocontrol agent may be;
 Necrogenic pathogen (applied on leaf).
 Non-pathogenic bacteria (PGPR) (applied to root or seed).
 Metabolites of pathogenic or saprophytic bacteria.

18. Mode of actions of biocontrol
Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58.
Microbial metabolites able to induce ISR
 Polyacrylic acid
 Ethylene
 Salicylic acid
 Acetyl salicylic acid
 Amino acid derivatives
 Harpin ( Erwinia amylovora)
• Stress can induce defense mechanisms against pathogens

19. Mode of actions of biocontrol
Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58.
Physical thickening of cell walls by;
 Lignification.
 Deposition of callose.
 Accumulation of antimicrobial low-molecular-weight substances (e.g.,
phytoalexins).
 Synthesis of various proteins (e.g., chitinases, glucanases, peroxidases, and
other pathogenesis related (PR) proteins).
Induced systemic resistance- defense responses

20. Mode of actions of biocontrol
Ahanger et al., 2014; Lee et al., 2015
Induced systemic resistance- defense responses
C. Induced systemic
resistance by biocontrol
agent Bacillus
amyloliquefaciens HK34
B. Plant treated with
0.1mM benzothiadiazole
(positive control)
A. Plant treated
with distill
water

21. Biocontrol application methods
 There are five application methods

22. Biocontrol application methods
1. Seed treatment

23. Biocontrol application methods
2. Seedling dip method

24. Biocontrol application methods
3. Soil drench

25. Biocontrol application methods
4. Foliar spray

26. Biocontrol application methods
5. Irrigation drips

27. Biocontrol application methods
1. Seed treatment
2. Dipping
3. Drench
4. Foliar prays
5. Drips
Ahanger, R., Bhatand, H. A., & Dar, N. A. (2014). Biocontrol agents and their mechanism in plant disease management. Sci Acta Xaver, 5, 47-58.

28. Requirements for successful biocontrol agents
1. Able to compete and persist
2. Able to colonize and proliferate
3. Must be non-pathogenic to host and environments
4. Must have excellent shelf life
5. Must be inexpensive
6. Must be able to produce in large quantities
7. Able to maintain viability
8. Delivery and application methods must support product establishment.
http://flax.nzdl.org/greenstone3/flax?c=BAWELS&a=d&rt=r&d=D2712&dt=simple&p.a=b&p.s=ClassifierBrowse&cls=

29. Limitations of biological control
1. Expensive/difficult to develop
2. Handling requires training
3. High Selectivity/Host Specificity
4. Variability in effectiveness
5. More susceptible to environmental conditions
6. Short shelf-life of formulations
7. Slow action
8. Storage Problem
http://flax.nzdl.org/greenstone3/flax?c=BAWELS&a=d&rt=r&d=D2712&dt=simple&p.a=b&p.s=ClassifierBrowse&cls=

30. Commercial biological control
 Active microbe: Bacillus subtilis strain GB03
 Mode of actions: Antibiosis
 Company : Gustafson, Inc, Plano, TX, USA
Junaid, J. M., Dar, N. A., Bhat, T. A., Bhat, A. H., & Bhat, M. A. (2013). Commercial biocontrol agents and their mechanism of action in the management of plant pathogens. International Journal of Modern Plant & Animal Sciences, 1(2), 39-57.

31. Commercial biological control

32. Some commercial biological control agents
Control of blue mold and gray mold on cherries,
apples, citrus.
Mode of action: Competition
Applicational methods:
• Dip or Drench
• Spray
Control of seed rot, root and stem rot and wilt caused
by Fusarium, Alternaria and Phomopsis on
ornamentals aand vegetables
Mode of actions:
Competition; Hyperparasitism; Antibiosis
Junaid, J. M., Dar, N. A., Bhat, T. A., Bhat, A. H., & Bhat, M. A. (2013). Commercial biocontrol agents and their mechanism of action in the management of plant pathogens. International Journal of Modern Plant & Animal Sciences, 1(2), 39-57.

33. Summary
 Biological control involves the use of microbial antagonists such as bacteria or fungi to
suppress plant disease pathogens.
 Biocontrol have several importance and advantages over other control methods
 Their mode of actions include antibiosis, competition, parasitism and induced systemic
resistance.
 There are however some limitations to the general use of biological control agents such
variability in effectiveness, low spectrum action, short shelf life of products etc.
 Some of the commercial available biocontrol agents include Biosave, Kodiak, Mycostop etc.
 A biological control agent can be applied as seed treatment, root dip, soil or furrow drench,
foliar sprays or through drip irrigation.

34. Thanks
Any question?

35. • Junaid, J. M., Dar, N. A., Bhat, T. A., Bhat, A. H., & Bhat, M. A. (2013). Commercial biocontrol agents and their
mechanism of action in the management of plant pathogens. International Journal of Modern Plant & Animal
Sciences, 1(2), 39-57.
• Jetiyanon, K., Fowler, W. D., & Kloepper, J. W. (2003). Broad-spectrum protection against several pathogens by
PGPR mixtures under field conditions in Thailand. Plant Disease, 87(11), 1390-1394.
• Lee, B. D., Dutta, S., Ryu, H., Yoo, S. J., Suh, D. S., & Park, K. (2015). Induction of systemic resistance in Panax
ginseng against Phytophthora cactorum by native Bacillus amyloliquefaciens HK34. Journal of ginseng
research, 39(3), 213-220.
• Koutb, M., & Ali, E. H. (2010). Potential of Epicoccum purpurascens Strain 5615 AUMC as a biocontrol agent of
Pythium irregulare root rot in three leguminous plants. Mycobiology, 38(4), 286-294.
• Kilic-Ekici, O., & Yuen, G. Y. (2003). Induced resistance as a mechanism of biological control by Lysobacter
enzymogenes strain C3. Phytopathology, 93(9), 1103-1110.
Sources