INTRODUCTION TO THE SCIENCE OF PHYTOPATHOLOGY: ITS IMPORTANCE, SCOPE AND CAUSES OF PLANT DISEASES

Question 1

Plant Pathology
Its relation to sciences

Answer 1

Plant Pathology, also known as Phytopathology is a branch of agricultural, biological
or botanical science which deals with the study of diseases in plants - their causes,
etiology, epidemiology, resulting losses and management.

Plant pathology is related to many other sciences such as virology, mycology,
bacteriology, microbiology, physiology, chemistry, genetics, biotechnology etc., all of
which provide the knowledge required for the correct diagnosis and management of
plant diseases.

Question 2

Objectives of Plant Pathology

Answer 2

To study living, non-living and environmental causes of diseases or disorders of the
plants.
 To study the mechanism of plant disease development.
 To study interaction between host/susceptible and the pathogens.
 To develop systems of management of plant diseases and reducing losses caused by
them.

Question 3

what is the difference between epidemiology and etiology?

Answer 3

Etiology and epidemiology are two distinct fields within the realm of medical and public health research, but they are closely related.

1. Etiology: This field focuses on the study of the causes or origins of diseases or disorders. It delves into understanding why certain conditions develop in individuals or populations. Etiological studies aim to identify risk factors, genetic predispositions, environmental exposures, and other elements that contribute to the onset and progression of diseases. Essentially, etiology seeks to answer the question “Why does this disease occur?”
2. Epidemiology: Epidemiology, on the other hand, is the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control health problems. It looks at the patterns, frequency, and spread of diseases within populations, exploring factors such as demographics, geography, behavior, and social determinants of health. Epidemiology is concerned with understanding the occurrence and spread of diseases, including how they are transmitted and what factors influence their incidence and prevalence.

In summary, while etiology focuses on the causative factors of diseases, epidemiology examines the broader patterns and determinants of disease occurrence within populations. Both fields play crucial roles in understanding and addressing public health challenges.

Sure! Imagine you have a garden with different types of plants.

1. Etiology: Think of etiology as trying to figure out why some plants in your garden get sick. Maybe some plants need more sunlight, some need more water, or some might be attacked by bugs. Etiology is like being a detective, trying to understand what makes certain plants get sick.
2. Epidemiology: Now, imagine you have lots of gardens in your neighborhood, and you notice that some gardens have more sick plants than others. Epidemiology is like studying all the gardens in your neighborhood to figure out why some neighborhoods have more sick plants overall. It looks at things like how many plants get sick, where they are, and what might be causing them to get sick.

So, etiology is about understanding why individual plants get sick, while epidemiology is about understanding why lots of plants in a whole area might get sick. Both are important for helping keep our gardens healthy!

Question 4

Why is it important to study plant pathology?

Answer 4

 Losses they cause.
 About 34% of the crop produce is lost annually due to diseases, insect-pests and
weeds on the global basis (Cramer, 1967); out of which, 12% is lost due to diseases
(caused by fungi, bacteria or viruses), 11% due to nematodes, 7% due to insect-pests
and 3% due to weeds.
 When plant protection measures are not implemented, annual loss of 30-50% are
common in major crops including horticulture (Encyclopedia Britannica, 2002).

Epidemics
 Late blight of potato caused by Phytophthora infestans was responsible for causing
Irish famine in 1845 by destroying the potato crop, the staple food of the people.
 Hundreds of thousand people died of hunger and disease, and there was a large scale
migration of the population to other countries including North American continent.
 The population of Ireland was 8 million in 1940, which was reduced to 4 million after
the famine.
 This single disease forced man to realize the importance of plant diseases, and
brought the science of Plant Pathology to lime light.

Other Famines
 Wheat rust epidemics occurred from time to time in many countries. Wheat rusts
forced farmers to change their cropping pattern and wheat was replaced by corn or
maize or rye.
 Brown spot of rice caused by Helminthosporium oryzae was responsible for Bengal
famine in 1943, which many people think one of the reasons for the division of
Bengal
 Coffee rust caused by Hemileia vastatrix forced to cut down the coffee plants in Sri
Lanka in 1867.
 Powdery mildew of grapevines caused by (Uncinula necator), by 1854, reduced the
French wine production by 80 per cent.
 In 1878, the downy mildew caused by Plasmopara viticola ultimately led to the discovery of Bordeaux mixture.

Losses in India
 Wheat rusts cause a loss of Rs. 400 crore annually.
 In the years of epidemics, losses are Rs. 5000 crore or more.
 Loose smut of wheat is estimated to cause an average loss of 3 per cent (about Rs. 500
crore) every year.
 Other plant diseases such as red rot of sugarcane, potato viruses, rice blast and blight,
Karnal bunt of wheat, root knot of tomato, eggplant and cucurbits, apple scab, mango
malformation, bunchy top of banana and sandal spike are responsible for huge losses.

Effect on Society
Infected grains or the fruits may contain toxins (such as aflatoxin, fumonosin) which
cause insanity, paralysis, stomach disorder and liver cancer.
 The money spent on the management of plant diseases is also a loss because in the
absence of diseases this money could be saved.
 There are many other implications on the transport and agro-based industry in the
event of plant disease inflicted yield loss.
 There is restriction on the movements of food grains and other agricultural produce
due to the threat of quarantine pathogens and pesticide residues in the produce causing further loss.

Question 5

Causes of Plant Diseases

Answer 5

Plant diseases are caused by a variety of pathogens.
 The word pathogen can be broadly defined as any agent or factor that incites
‗pathos‘ or disease in an organism. Thus in strict sense, the pathogens do not
necessarily belong to living or animate groups.
1.Abiotic (Inanimate) factors
2.Mesobiotic causes
3. Biotic (Animate) causes

Question 6

Abiotic (Inanimate) factors

Answer 6

They include mainly the deficiency or excess of nutrients, light, moisture,
aeration, abnormality in soil condition, atmospheric impunities etc.
Examples are: Black tip of mango (due to SO2 toxicity), khaira disease of
rice (due to Zn deficiency), whiptail of cauliflower (Mo deficiency), hollow
and black heart of potato (due to excessive accumulations of CO2 in
storage), bitter pit of apple (due to Ca deficiency).

Question 7

Mesobiotic causes

Answer 7

These are the disease incitants which are neither living nor non-living. They
are considered to be on the threshold of life. They are:
 Viruses: They are infections agents made up of one type of nucleic acid
(RNA or DNA) enclosed in a protein coat. Examples of viral diseases of
plants are: potato leaf roll, leaf curl of tomato and chillies, and mosaic
disease of many plants.
 Viroids: They are naked, infectious strands of nucleic acid. They cause
diseases like potato spindle tuber, citrus exocortis, chrysanthemum stunt,
cadang cadang of coconut palm, star crack of apple, etc.

Question 8

Biotic (Animate) causes

Answer 8

This category includes the pathogens which are animate or living or cellular
organisms. They are:
 **Prokaryotes **like bacteria which are unicellular prokaryotic microorganisms
lacking true nucleus. Examples of diseases caused by true bacteria are:
brown rot or wilt of potato, soft rot of potato and vegetables, , citrus canker,
etc. i) Phytoplasma are wall-less prokaryotes and cause diseases like peach X.
ii) Fastidious bacterium, Xylella fastidiosa causes almond leaf scorch,
Pierce‘s disease of grapevine.

 Eukaryotes are the organisms with true nucleus.
i) Fungi: Potato wart, powdery mildew, rust, smuts, red rot of sugarcane (nearly
80% of plant diseases are caused by fungi).
ii) Straminopiles (Oomycetes): Downy mildews, late blight of potato, white rust of
crucifers, damping off etc.
iii) Protozoa: Hart rot of coconut palm and phloem necrosis of coffee.
iv) Algae: Red rust of mango or papaya or litchi
v) Metazoan animals (Nematodes): Root knot of vegetables, ear cockle of wheat,
citrus decline etc.
vi) Parasitic flowering plants (Phanerogamic plant parasites): Dodder, Striga,
Orobranche, Loranthus, Phoradendron, etc.