Biological Control Lec - PowerPoint Presentation

Slide1

Biological Control Lec = 3

Slide2

Mechanisms of Biological Control Because biological control can result from many different types of

interactions between organisms, researchers have focused on characterizing the mechanisms operating in different experimental situations.

In

all cases, pathogens are antagonized by the presence and activities of other organisms that they encounter. Here, we assert that

the different mechanisms of antagonism occur across a spectrum of directionality related to the amount of

interspecies contact

and

specificity of the

interactions

Slide3

1.

Direct mechanism:

Direct lysis or killing of pathogen by biocontrol agent

a)

Antibiosis

(Enzyme,

Hydrogen

Cyanide,

Plant growth promotion

b)

Parasitism

2.

Indirect mechanism:

Exclusion of plant pathogen as a result of the presence,

activity or

products of biocontrol agent.

a)

Competition

b)

Induced systemic

resistance

Slide4

Direct mechanisma) Antibiosis:

Antibiosis is defined as antagonism mediated by specific or non-specific

metabolites of microbial origin, by lytic agents, enzymes, volatile compounds or other toxic substances.

Antibiosis

plays an important role in

biological control. Antibiosis is a situation where the metabolites are secreted by underground parts of plants, soil microorganism, plant residues etc. It occurs when the pathogen is inhibited or killed by metabolic products of the antagonists. The products include the lyric agents, enzymes, volatile compounds and other toxic substances.

Slide5

Hydrogen cyanide: Many rhizobacteria produce hydrogen cyanide and this has been shown to play direct as well as indirect role in biological control of plant diseases and increasing the yields. The florescent pseudomonas themselves produce HCN and are able to suppress the pathogens.

Slide6

Lytic enzymes: Lysis is the complete or partial destruction of a cell by enzymes. Lysis may be distinguished into two types,

Endolysis and

Exolysis

.

Endolysis

(autolysis) is the breakdown of the cytoplasm of a cell by the cell’s own enzymes following death, which may be caused by nutrient starvation or by antibiosis or other toxins.

Endolysis

does not usually involve the destruction of the cell wall.

Exolysis

(heterolysis) is the

destruction of cell by the enzymes another organism

. Typically

exolysis

is the destruction of the walls of an organism by

chitinases

,

cellulases

etc. and this frequently results in the

death

of the attacked cell.

Slide7

Plant growth promotion: Biocontrol agents also produce growth hormones like, Auxins,

Cytokinin, Gibberellins etc. These hormones suppress the

deleterious pathogens

and promote the growth of plants and simultaneously increase the yield

.

The PGPR (Plant Growth-Promoting Rhizobacteria ) promotes plant growth directly by production of plant growth regulators or indirectly by stimulating nutrient uptake, by producing side

rophores

or antibiotics to protect plant from soil borne pathogens or deleterious rhizosphere organisms. Pseudomonas spp. May increase plant growth by producing gibberellins- like substances, mineralizing phosphates. For growth of agricultural production has led several new challenges, making further growth possible only if these challenges are met appropriately and timely. Increase in crop production from the modern farming techniques reaching a plateau is the most of the countries including India and the environmental problems due to excessive use of chemical fertilizers and pesticides becoming a matter of concern. So, the biological control can be alternate system, which may play an important role in achieving the goal of agriculture.

Slide8

Slide9

b) Parasitism It is a coexisting relation in which two microorganisms that are not evolutionally related to each other live together for a long period of time, and as a result of this kind of relation, usually one of these two types of microorganisms which is physically smaller and is called the parasite, benefits from the other one which is partially damaged and is called the host. The most direct type of competition in a biological control is

hyperparasitism

in which pathogenic parasites are used to eliminate a pathogen. The most direct type of competition in biological control is

hyperparasitism

, in which obligate parasites are used to eliminate the same plant pathogen . Biological control also means a reduction in nematode damage by organisms antagonistic to nematodes through the regulation of nematode populations and/or a reduction in the capacity of nematodes to cause damage, which occurs naturally or is accomplished through the manipulation of the environment or by the mass introduction of antagonists .

Biological systems can improve the soil consistency and maintain natural soil flora. Microorganisms from each rhizosphere soil develop the plant resistance against pathogens .

Slide10

Slide11

Mode of actions of

biocontrol

Steps

involved

in

Mycoparasitism

Chemotropic

growth:

t

he

biocontrol fungi grow toward the

target

fungi

chemical stimuli.

Recognition

stage:

interaction

between biocontrol receptors and that of the host

fungus

Attachment and

cell

wall

degradation

(chitinases and

glucanases).

Penetration (

appressoria-like

structures).

Slide12

Mode of actions of

biocontrol

Ahanger

et al.,

2014;

Dubey and

Dwivedi,

1986.

Steps

involved

in

Mycoparasitism

m

ul

i

.

s

. Chemotropic growth: the biocontrol fungi grow toward the target fungi chemical sti. Recognition stage: interaction between biocontrol receptors and that of the host fungu. Attachment and cell wall degradation (chitinases and glucanases).. Penetration (appressoria-like structures).

H

yperparasite (bicontrol)1234

Coiling

Penetration

Barrier formation by host hypha

Branching and sporulation

Chlamydospores formation

Lysis of host hypha

Host

fungus

(pathogen)

hypha

Source:

biocylopedia.com

Slide13

Mycoparasitism /

Hyperparasitism:

Occurs when

the antagonist invades the

pathogens.

Mycoparasitism is the phenomenon of one fungus being parasitic on another fungus by secreting enzymes such as chitinases, celluloses, glucanases and other lytic enzymes.

The

parasiting

fungus is

called

hyperparasite

and the parasitized fungus as

hypoparasite

.

In

mycoparasitism

, two mechanisms operate among involved species of fungi. This may be hyphal of inter fungus interaction i.e., fungus-fungus interaction, several events take place which lead to predation viz., coiling, penetration, branching and sporulation, resting body production, barrier formation and lyses

.

 

Slide14

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.

Slide15

There are two main groups of mycoparasite

Biotrophic

and necrotrophic

mycoprasites

1-

Biotrophic mycoparasites

Get

nutrients

from living host cells

and their growth of these parasites is greatly influenced by the metabolism of the host.  

Biotrophic

mycoparasites

tend to have a

high host specificity

, and often form

specialized

infection structures or a host parasite transition

.  2- Necrotrophic mycoparasites could only rely on saprophyte  growth.

 On the other hand, the antagonistic action is strongly aggressive in necrotrophic relationships which is dominated by necrotrophic mycoparasites . Necrotrophic parasites tend to have a low host specificity, and are relatively unspecialized in their mechanism of parasitism

Slide16

Indirect mechanism

Competition ( Food / Space)

I

t

is a kind of mutual coexistence between two living microorganisms, which occurs when different microorganisms within a population attempt to achieve something similar. The target may be a place or food .

Microorganism competes for

space, minerals

and

organic nutrients

to proliferate and survive in their natural habitats. This has been reported in

both rhizosphere

as well as

phyllosphere

.

Competition

has been suggested to a play a role in the biocontrol of species of

Fusarium and Rhizoctonia by some strains of Aspergillus niger

Slide17

Antagonism

It is the negative effect that a microorganism has on another one. This is a one-way process and is due to the production of certain compounds such as antibiotic or bacitracin produced by a

microorganism

Slide18

Competition for substrates is the most important factor for heterotrophic soil fungi. Success in saprophytic ability (CSA) and inoculums potential of that species. Those fungi with highest number of propagules or the greatest mass of mycelia growth have the greatest competitive advantage.

Competitive

saprophytic

ability is the summation of physiological characteristics that make for success in competitive colonization of dead organic substrates

.

Slide19

Slide20

b)

Induced

Systemic Resistance (ISR

):

ISR is the ability of an agent (a fungus, bacteria, virus, chemical etc.) to induce plant defense mechanisms that lead to

systemic resistance

to a number of pathogens.

Inoculation

of plants with weak pathogens or non- pathogens leads to induced systemic plant resistance against subsequent challenge by pathogens. The mechanisms remain largely unknown but typically the induced resistance operates against a wide range of pathogens and can persist for 3-6 weeks. The biocontrol agents bring about induced systemic resistance (ISR) through

fortifying the physical and mechanical strength of cell wall as well as changing physiological and biochemical reaction of host leading to the synthesis of defense chemicals against challenge inoculation of pathogens.

Defense reaction occurs due to accumulation of

Pathogenesis-related

PR

proteins

(

chitinase

, B-1, 3

glucanse), chalcone synthase, phenylalanine ammonia lyase, peroxidase, phenolics, callose, lignin and phytoalexins.

Slide21

Indirect effects of Biological control

Ecological Replacement’

Compensatory

Response’

By

a weed or pest following attack by a biocontrol agent, which might

increase negative interactions

between the

target

and

non-target

species

..

Describes

the potential for

non-target impacts through reduction of a pest or weed

that has become integrated into a native community.

Slide22

Ecological Basis of Biocontrol

One organism can be used to control another

Some

organisms have a limited host range

Biocontrol agents released into invasive plant populations must

not only survive and multiply

in their new environment, but they must also

attack and cause enough damage to their host

to cause significant population decline.

Biocontrol is used to reduce invasive plant populations to levels below damaging thresholds, not to eradicate plant species. Because biocontrol agents rely on sufficient host plant populations to provide their food and habitat, they will not completely eliminate their host plant populations. 

To reduce dominance of an invasive plant within the plant community, effective biocontrol agents must focus their actions upon the target plant without harming other vegetation. To be considered for release in the United States, insect biocontrol agents must feed and develop only on the target plant, and in some cases, only on a few closely related plant species. This is known as host-specificity and is the most important precondition for an insect to be used as a biocontrol agent.

Slide23

Potential biocontrol agents often undergo five or more years of rigorous testing to ensure that host-specificity requirements are met. For example, surveys and host-specificity testing for potential biocontrol agents for purple loosestrife began in Europe in 1986. The first releases in the United States were made seven years later, following resolution of concerns surrounding non-target feeding impacts on other plant species . One agent under consideration was not proposed for introduction because it exhibited a wider host range .

Slide24

Integrated Pest Management (IPM) systems.

An IPM approach can provide direct benefits to farmers through regular monitoring of crops for pests.

This enables farmers to make decisions based on observations, and use an optimum mix of pest control techniques and tools which bear in mind the economic threshold level, risks associated with control selection as well as environmental and human safety.

The IPM approach is particularly important for tillage farmers as it has become

increasingly difficult to control pests using a single approach.

This dependence can also be considerably

costly in the long-term.

Integrated pest management is a dynamic and evolving practice. Specific management strategies will vary from

crop to crop

,

location to location

, and

year to year

, based upon changes in pest populations and their natural controls. As specific new approaches are developed, these too can be incorporated into the program as appropriate. Modern pest managers will be most effective if they are knowledgeable about their pests, beneficial, and all of the control options available.

Slide25

Those who practice IPM realize that it is neither possible nor economically feasible to eliminate all pests; instead pest populations should be managed below economically damaging levels.

Users

of the IPM approach recognize and understand the importance of the controls provided by

nature.

When

human intervention is necessary, the

least invasive

practices, such as plant resistance, biological control, and cultural control, should be used because these are the practices that fit best into sustainable agriculture

.

Highly

disruptive or environmentally damaging practices should be used only as a last resort.

Chemical

pesticides

should be used

only when necessary

, based upon frequent and routine monitoring of pest populations. Natural enemy populations should also be monitored so that their impact on pests can be determined. When pesticides are necessary, if possible, only those products should be used that are not detrimental to natural

enemies

Slide26

Slide27

There are three main methods of population control – physical, chemical and biological

Slide28

Physical ControlPhysical control involves the removal or restriction of invasive species by manual or mechanical measures

This may include the installation of barriers and fences or the removal of habitat by excavation or trimming

Population numbers may be reduced by hunting, trapping and culling, although these methods are

lab our

intensive

Physical methods to contain invasive species are not usually species specific and can also impede endemic wildlife.

Slide29

Chemical Control

Chemical control involves the use of chemical agents (poisons and toxins) to limit population numbers and spread

Chemical

agents may include herbicides (for plants), pesticides (for insects) or other compounds (e.g. rat poison)

Chemical agents may have moderate specificity, but can also detrimentally affect local wildlife and are costly to employ

The effect of chemical agents may become more pronounced in higher trophic levels due to bio magnification

Slide30

Biological Control

Biological control involves using a living organism (or a virus) to control an invasive species

The biological control may eat the invasive species (predation) or cause it to become diseased

Biological agents must be carefully assessed before release to ensure they do not become invasive themselves

Examples of agents include the

Vedalia beetle (feeds on citrus plant invertebrates) and the

Myxoma

virus (infects rabbits)

Biological control agents must be monitored for unintended side effects (e.g. development of immunity in invasive species)

Slide31

The

use of

biological, physical and non-chemical control methods

must be preferred to

chemical options

as long as the non-chemical options provide acceptable pest control.

Intelligent production practices shall be used

. These can include crop rotation, sustainable cultivation techniques, resistant/tolerant cultivars and certified seed production systems, balanced fertilization, irrigation and drainage techniques, the protection and proliferation of beneficial organism.

In

the event that

pesticides must be applied

, they shall be target-specific and strategically applied in an effort to reduce negative health outcomes

.

In cases where

pest resistance

has been established and repeat pesticide application is necessary, anti-resistance strategies should be integrated into control efforts.  

Record

keeping

is essential and should be based on

detailed records in order to determine the efficacy of pest control programs – especially in the case of chemical inputs.

Monitoring efforts are essential in order to track pest presence.  This can be accomplished via observations, forecasting and early diagnosis systems and information, as well as information from professionally qualified.  The 6 principles of IPM are as followed: