Phytopathology
(Phyton : plant) Greek - Pathos (suffering) + Logos (study) = The study of the suffering
plant.Plant Pathology is defined as the study of the
organisms and environmental conditions that cause disease in plants, the
mechanisms by which this occurs, the interactions between these causal agents
and the plant (effects on plant growth, yield and quality), and the methods of
managing or controlling plant disease. It also interfaces knowledge from other
scientific fields such as mycology, microbiology, virology, biochemistry,
bio-informatics, etc.Plant
pathology (also phytopathology) is the scientific study of plant diseases caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomycetes, bacteria, viruses,viroids, virus-like organisms, phytoplasmas, protozoa, nematodes and parasitic plants. Not included are ectoparasites like insects, mites, vertebrate, or other pests that affect plant health by consumption of plant tissues. Plant pathology also involves the study of pathogen identification, disease etiology, disease cycles, economic impact, plant disease epidemiology, plant disease resistance, how plant diseases affect humans and animals, pathosystem genetics, and management of plant diseases.
WHAT IS A PLANT DISEASE?
1. A plant disease is any abnormal condition that alters the
appearance or function of a plant. It is a physiological process that affects
some or all plant functions. Disease may also reduce yield and quality of
harvested product.
2. Disease is a process or a change that
occurs over time. It does not occur instantly like injury.
3. Visible effects of
disease on plants are called symptoms.
Any detectable changes in color, shape, and/or functions of the plant in
response to a pathogen or disease-causing agent is a symptom.
•Signs of plant disease are physical evidence
of the pathogen, for example, fungal fruiting bodies, bacterial ooze, or
nematode cysts. Signs also can help with plant disease identification.
OBJECTIVES OF PLANT
PATHALOGY
1. Study of origin, causes or
reasons. Study of living, non-living and other causes of disease or disorder in
plants- Etiology:
2. Study of mechanism of disease
development i.e. processes of infection and colonization of the host by the
pathogen. This phase involves complex host-pathogen interactions- Pathogenesis
3. study the interaction between
the causal agent and the diseased plants in relation to environmental
conditions. Generally at the population level- Epidemiology
4. Development of management
systems of the diseases land reduction of losses caused by them- Control/ Management.
WHAT CAUSES PLANT DISEASE?
1.
Infectious plant diseases are caused by living organisms that attack and obtain
their nutrition from the plant they infect. The parasitic organism that causes
a disease is a pathogen. Numerous fungi, bacteria, viruses, and
nematodes are pathogens of corn and soybean in Iowa.
2.
The plant invaded by the pathogen and serving as its food source is referred to
as a host.
ROLE OF THE ENVIRONMENT
1.
A favorable environment is
critically important for disease development – even the most susceptible plants
exposed to huge amounts of a pathogen will not develop disease unless
environmental conditions are favorable.
THE CONCEPT OF DISEASE IN PLANTS
plant is healthy, or normal, when
it can carry out its physiological functions to the best of its genetic
potential.
Any deviation- Disease
1. The
kinds of cells and tissues that become affected determine the type of
physiological function that will be
2. For
example, infection of roots may cause roots to rot and make them unable to
absorb water and nutrients from the soil;
3.
infection of xylem vessels, interferes with the translocation of water and
minerals to the crown of the plant;
4.
infection of the foliage, (leaf spots, blights, rusts, mildews, mosaics etc.),
interferes with photosynthesis
WHAT IS A DISEASE
Stakman &
Harrar (1957) defined disease as physiological disorder or structural
abnormality that is deleterious to the plant or its part or product, that
reduces the economic value of the plant e.g., wilt, potato blight, Loose smut
of wheat, karnal bunt of wheat
DISEASE
1.
Disease –
the process in which a pathogen interferes with one
or more essential plant cell functions
2. Marshall Ward (1901): disease represents a
condition in which functions of the plant are not properly
discharged.
3. Disease is a harmful deviation from
normal functioning of physiological processes. (British Mycological Society,
1950)
4. Horsfall & Diamond (1957): Disease
can be defined as a physiological disorder or structural abnormality that is
deleterious or harmful toe the plant or its part or product that reduces its
economic value.
Disease can
be defined as the result of interaction between host, pathogen and environment
HOW PATHOGENS AFFECT PLANTS
There are many ways in which plant disease pathogens
can affect plants
1. By utilizing host cell contents
2. By killing host or by interfering with its
metabolic processes through their enzymes, toxins etc.
3. By weakening the host due to continuous loss
of the nutrients.
4. By interfering with the translocation of the
food, minerals land water.
5. They can suppress the chlorophyll content.
6. They can reduce the leaf area.
7. They can curb the movement of solutes and
water through the stems.
8. They sometimes reduce the water-absorbing
capacity of the roots.
9. They suppress the translocation of
photosynthates away from the leaves.
10. They sometimes promote wasteful use of the products
of photosynthesis as in the formation of galls.
CLASSIFICATION OF PLANT DISEASE
1.
Based on type of symptoms
a. Blights
b. Rusts
d. Rots
e. wilts
2. Based on type of crop
a. Cereal diseases
b. Vegetable diseases
c. Fruit
3.
Based on type of organ affected
a. Fruit diseases
b. Root diseases
4. Based on cause:
I a. Infectious diseases
b. Non-infectious diseases
PLANT DISEASE AGENTS
a. Living organisms - including fungi, bacteria, viruses and nematodes
b. Nonliving agents - including unbalanced soil fertility,
toxic chemicals, air pollution, frost, drought, sunburn, wind and hail.
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