Basic concepts in plant
pathology
Plant pathology: is a
science that studies plant diseases and attempts to improve the chances for
survival of plants when they are faced with unfavorable environmental conditions
and parasitic microorganisms that cause disease. As such, plant pathology is
challenging.
A
plant disease: is a Series of invisible and visible
responses of plant cells and tissues to a pathogen or environmental factor
that result in adverse changes in the form, function, or integrity of the plant
and may lead to partial impairment or death of the plant or its part.
Diseases result from more or
less continuous irritation of the plant tissues by a primary causal agent. Disease
is a process that takes time, is physiological in nature, abnormal, and detrimental.
Diseases cause damage by reducing yield and/or quality of plants and/or plant
products.
Plant problems may be caused by
either living (biotic ) or non-living
(abiotic) factors. Living factors are infectious (they spread from plant to
plant). These include pathogens (fungi, nematodes, bacteria, and viruses),
insects, and other animals. Non-living factors that cause plant problems do not
spread from plant to plant. They are caused by chemical, physical, or
mechanical factors. Examples of these abiotic factors include nutrient
deficiencies and water or temperature stress.
Principles of plant disease diagnosis
Diagnosis of plant diseases requires
consideration of various biotic and abiotic factors which may be involved in
the causation of disease, as well as a sound knowledge of the host plant
symptoms and signs. Many variables may influence each situation, including the
state of the host, its cultural history, weather conditions, soil and general
site characteristics. A good understanding of the "normal host" is
essential, and experience is invaluable!
The complexity of the etiology
(cause) of the disease usually determines the difficulty of diagnosis. Many
diseases in which a single pathogen is the principal causal agent have
distinguishing and characteristic associated symptoms and signs. Diseases with
more complex etiology may have symptoms which suggest several possible causes,
and may be difficult to diagnose precisely.
One of the first considerations in
the art and science of diagnosis is to attempt to determine whether an
infectious agent is involved. This often requires laboratory examination,
including procedures for examining critical features with stereo and compound
microscopes, and for isolation of associated microorganisms in pure culture on
artificial media. The key means of demonstrating causality is application of
Koch s Postulates. However, in practice, in disease diagnostic clinics, there
is typically neither the time nor the resources to perform Koch’s Postulates,
so the cause of disease must be inferred based on the weight of evidence and
knowledge of the host plant.