Biotic stress

Stress

Difficulty that cause worry Or an Environmental damage to plants

Biotic abioticResistance ： The adaptability of plants to adverse environment

◇Stress avoidance ◇ Stress tolerance

Plants are sessile and must deal with stresses in placePlants cannot avoid stress after

germinationHow plants deal with stress has

implications in Ecology: Stress responses help explain

geographic distribution of speciesCrop science: Stress affects productivityPhysiology and biochemistry: Stress affects

the metabolism of plants and results in changes in gene expression

Plants are sessile and must deal with stresses in place• From engineering, stresses cause

strains (responses of stressed objects) = changes in gene expression and metabolism in plants

• Biological stress difficult to define/quantify:

Types of stress

Types of resistance

Biotic Stress and Plant Defense Responses Pathogen Strategies1. Necrotrophic – plant tissue killed and then

colonized; broad host rangee.g., rotting bacteria (Erwinia)

2. Biotrophic – plant cells remain alive, narrow host range (1 plant species)

e.g., viruses, nematodes, fungal mildews

What causes a plant to be stressed? As with humans, stresses can originate from the surrounding environment (called abiotic, or nonliving stresses); or, they can come from living organisms that can cause disease or damage (caused biotic stresses).

Biotic stressBiotic Stress is stress that occurs as

a result of damage done to plants by other living organisms, such as bacteria, viruses (although they are not considered to be living organisms, also cause biotic stress to plants), fungi, parasites, beneficial and harmful insects, weeds, and cultivated or native plants.

Biotic stressThe damage caused by these various living and nonliving agents can appear very similar.[2] Even with close observation, accurate diagnosis can be difficult.

Biotic stressFor example, browning of leaves on an oak treecaused by drought stress may appear similar to leaf browning caused by oak wilt, a serious vascular disease, or the browning cause by anthracnose, a fairly minor leaf disease.

Agriculture

It is a major focus of agricultural research, due to the vast economic losses caused by biotic stress to cash crops.

Agriculture The relationship between biotic stress and plant yield affects economic decisions as well as practical development.

Agriculture  Plants are exposed to many stress

factors, such as drought, high salinity or pathogens, which reduce the yield of the cultivated plants or affect the quality of the harvested products. Arabidopsis thaliana is often used as a model plant to study the responses of plants to different sources of stress.[5]

Biotic stressesFungi cause more diseases in plants than any other biotic stress factor.

Over 8,000 fungal species are known to cause plant disease.

On the other hand, only about 14 bacterial genera cause economically important diseases in plants,

Biotic stresses According to an Ohio State University Extension publication.

Not many plant pathogenic viruses exist, but they are serious enough to cause nearly as much crop damage worldwide as fungi, 

 Microorganisms can cause plant wilt,

leaf spots, root rot, or seed damage.

. Insects can cause severe physical damage to plants, including to the leaves, stem, bark, and flowers. Insects can also act as a vector of viruses and bacteria from infected plants to healthy plants.

Biotic stressesThe method by which weeds, considered as

unwanted and unprofitable plants, inhibit the growth of desirable plants such as crops or flowers is not by direct damage, but by competing with the desirable plants for space and nutrients.

Because weeds grow quickly and produce an abundance of viable seed, they are often able to dominate environments more quickly than some desirable plants.

Plant defenses1) Physical barriers: cuticle, thorns, cell walls2) Constitutively produced chemicals (e.g.,

phytoalexins) and proteins (e.g., Ricin) 3) Induced responses (a.k.a., the Plant Defense

Response)

Plant defense

Ephemeral plants

Ephemeral plants avoid stress in US desert Only bloom after wet winterDie before summer returns

Alfalfa & CAM plants Avoidance also possible by

morphological adaptationsDeep tap roots in alfalfa allow growth in

arid conditions– Desert CAM plants store H2O in fleshy

photosynthetic stems. Adaptation: heritable modifications to increase fitness

• CAM plants’ morphological and physiological adaptations to low H2O environment

FernsStress resistant plants can tolerate a particular stress

Resurrection plants (ferns) can tolerate dessication of protoplasm to <7% H2O can rehydrate dried leaves

Plants may become stress tolerant through

Cold hardy plants–Acclimation: non heritable physiological and biochemical gene expression• Cold hardening induced by gradual exposure to chilling temps, cold-hardy plants

Pathogen invasion

Pathogen invasionApoptosis : Cell suiside mechanism.

at invasion site to physically cut off rest of plant

Assignment of : physiology Submitted to : Dr. ameer Submitted by : Mujahid hussain Roll No. : 127 Class : Bs botany 6th (S.S)

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