1. Biotic stress in plants
Introduction
Stress is a biological condition of a plant
resulting from the influence of some
environmental factors that adversely affect
its complete growth and development.
Depending on the nature there are mainly
two types these are biotic stress and abiotic
stress.
2. Biotic stress
This type of stress occurs as a result of
damage done to plants by other living
organisms such as
Fungi
Bacteria
Virus
Nematodes ,harmful insects and weeds etc
3. History
Biotic stresses have huge effect on plants in
this way cause different loss. For example the
potato blight , an oomycete which caused
widespread famine in England,Ireland and
Belgium in the 1840.
Another example is grape phylloxera coming
from North America in the 19 century which
lead to the Great French wine Blight.
4. Plant affected by disease is known as host
,while the organism that produce the disease
is termed as pathogen.
Some diseases are mention below
Late bight of potato,black rust of wheat
Mosaic of tomato and tobacco,citrus cancer
Crown gall of vascular plants
5. General losses due to disease
Killing of plants
Damage to the leaf tissues
Damage to reproductive organs including
fruits and seeds.
Besides the pathogenic attacks, insects also
lead certain major damage economically
important plants.
For example cotton is attacked by more than
60 species of harmful insects
6. Certain losses due to insects
Reduced growth
Premature defoliation
Wilting of plants
Serves as vectors for some pathogen making
the plants vulnerable for further pathogenic
infection
7. Physiological alteration in
host plant due to biotic stress
Photosynthesis is tremendously decrease after
pathogenic infection.This is carried out by
Reduction in photosynthetic area the plant
disease
that attack green aerial tissues like leaf spot,
blight
render harmful effects by destructing
photosynthetic leaf tissue or defoliation which
result in lessening the photosynthetic area
thereby reducing the photosynthesis.
8. Transpiration
Rate of transpiration increases in plants after
certain disease infection leaf rust,apple
scab,downy mildew
This is because these diseases result in
destruction of protection devices in plants
like cuticle,epidermis,increase permeability
of leaf cells resulting in uncontrolled loss of
water and loss of turgor to which wilting of
leaves follows.
9. Reduction in chlorophyll
content
Chlorosis is one of the most common
symptoms of plant disease and refers to the
destruction of chloropyll per chloroplast
It is resulted by viral infection e.g tobacco
mosaic disease etc
10. Effect of toxins
In some fungal and bacterial diseases.
Photosynthesis is reduced because of toxins
The toxins like tabtoxins inhibit some of the
enzymes that are directly involved in
photosynthesis
11. Reduction in activity of calvin
cycle
After disease infection the activity of some key
enzymes of calvin cycle is reduced due to
changes in the concentration of soluble
carbohydrates in infected tissues which in turn
effects photosynthetic fixation of carbon
dioxide.
In Arabidopsis, leaves infected by the biotrophic
fungus Albugo candida the reduction in the rate
of photosynthesis is parallel to decrease in the
amount of Rubisco enzyme present in the host
tissue.