Plant Pathology

Plant pathology is the study of illnesses brought on by plant pathogens, also called phytopathogens. Nematodes, bacteria, fungi, viruses, and protozoa are some of these pathogens. Phytopathologists are scientists who study plant pathology. Plant diseases can be caused by various pathogens, including both prokaryotic and eukaryotic organisms.

In this article, we will study the Definition and Principles of Plant Pathology, Types of plant pathogens, Fungal pathogens, Bacterial pathogens, Viral Pathogens, nematode pathogens, protozoa, and algae pathogens, Epidemiology of plant diseases, Prevention and Control of Protozoan Diseases and Importance of Plant Pathology.

Definition of Plant Pathology

Plant Pathology is a branch of biology that studies diseases caused by phytopathogens, including both prokaryotic and eukaryotic organisms.

Principles of Plant Pathology

The following are the key points and principles of plant pathology:

1. Plants experience disease when a pathogenic agent continues to cause them discomfort.
2. The same circumstances that promote plant health and development can also promote illness.
3. Plants that are submerged or overwatered both make the illness worse.
4. Reducing the inoculum is a key strategy for disease control.
5. Tree breakage and wind damage are caused by wood decay organisms.
6. Invasive species outbreaks are more serious than those caused by native species.
7. The most effective way to fight illness is frequent quarantine.

Types of Plant Pathogens

In order to start an infection at the site of damage, pathogens must release hydrolases, often referred to as cell wall degrading enzymes (CWDE), which help break down cell walls. Let’s discuss the different types of agents.

Fungal Pathogens

Ascomycota and Basidomycetes are the main classes of fungi that are responsible for causing diseases. Fungi produce spores that can resist extreme environments and are capable of feeding saprotrophically. There are two types of fungal pathogens:

• Biotrophic: These colonize the plant and obtain nutrients from it to flourish themselves.
• Necrotrophic: In order to get nutrients from the host, these diseases infect and kill the host.

Oomycetes

These are fungal-like pathogens due to their ability to progress disease in the same way as fungus does. Oomycetes have the ability to inhibit plant defenses by secreting effector proteins. They are basically responsible for root rot diseases.

Examples Of Fungal Agents

The following table depicts various pathogens of Kingdom Fungi:

Class Of Fungi	Name	Disease Caused
Ascomycetes	Fusarium spp	Fusarium wilt
Ascomycetes	Thielaviopsis spp.	Black root rot
Ascomycetes	Magnaporthe grisea	Rice blast
Ascomycetes	Sclerotinia sclerotiorum	Cottony Rot
Basidomycetes	Ustilago spp.	Barley smut
Basidomycetes	Phaskospora pachyrhizi	Soyabean rust
Basidomycetes	Puccinia spp.	Grass rusts
Oomycetes	Phytophthora spp.	Potato blight diseases
Oomycetes	Phytomyxea (Slime mould)	Clubroot in cabbage and Powdery scab in Potatotes.

Bacterial Pathogens

They are saprotrophic and do not harm the plant itself. Bacteria are responsible for several plant diseases in subtropical and tropical regions because of temperature requirements. Bacilli are main bacterial pathogens because they secrete several effector proteins to initiate the disease, which include CWDE, toxins, phytohormones, and Exopolysaccharides (EPS).

Examples of Bacterial Agents

Some examples of bacterial agents are :

• Erwinia spp. – Causes Soft rot by secreting CWDE
• Agrobacterium spp. – Causes tumours
• Pseudomonas syringae – Inhibits tomato fruit productivity

Viruses and Virus like Pathogens

Plant viruses are responsible for the loss of crops.They are asymptomatic and latent. Most plant viruses have ssRNA as a their genome but some have dsRNA or dsDNA as well. Mode of transmission is by vector in plants or sometimes through mechanical and seed transmission. Vectors includes insect like aphids, fungi, nematodes, protozoa.

Examples of Viral Pathogens

Few examples of Viral pathogens are

• Curly top virus – Causes leaf curling
• Tobacco mosaic virus – Causes mosaic disease

Nematodes Pathogens

These are small, multicellular worms which mainly infect root of the plant. They are mainly found in subtropical and tropical regions. Nematodes infect root of the plants to obtain water and other nutritent for their growth.

Examples Of Nematode Pathogens

Few examples of nematode pathogens are:

Globodera pallida and Globdera. rostochiensis – These infect potatoes and tomatoes. They also cause Potato cyst.

Protozoa and Algae Pathogens

They are transmitted as zoospores and survive for years. Zoospores are responsible for plasmodium formation in root hair to invade plant. An example is Phloem necrosis that causes disease in coffee plant.

Epidemiology of Plant Diseases

Pathogens infect plants in several ways, either by releasing toxins or enzymes that degrade cell walls. A few of these techniques are given below:

• Cell wall degrading enzymes (CWDE): These are the classes of proteins that are responsible for rupturing the plant cell wall to initiate the infection at the infection site. These include the hydrolase class of enzymes, which includes esterases, glycosyl hydrolases, lyases, and oxidoreductases.

• Toxins: There are two types of toxins that are released by plant pathogens:-

1. Non-host specific: which damages all plants
2. Host specific: which damages only the host plant

• Effector proteins: There are several effector proteins that can initiate plant infection. Pathogens secrete these effector proteins in an extracellular environment or inject them directly into the host plant via secretory system types. Pathogens like bacteria, fungi, and oomyctes are responsible for the secretion of effector proteins.

• Spores: Plant hosts may become infected by the spores of phytopathogenic fungi. Spores first cling to the host plant’s leaves and stems’ cuticular layer. Spores have the ability to form special hypae known as germ tubes, which can adhere to plant roots and initiate the infection by secreting CWDE.

Prevention and Control of Protozoan Diseases

Plant protozoan infections can be prevented and controlled by employing a variety of tactics designed to slow the pathogens’ spread. The following are some broad strategies for preventing and managing plant diseases caused by protozoa:

1. Maintaining and Changing the Crop: Make sure to maintain appropriate agricultural hygiene by getting rid of any contaminated plant material. By doing this, the inoculum source is lessened, and the transmission of protozoa to healthy plants is stopped. Rotate your crops to disrupt the life cycle of pathogenic protozoa. Refrain from consistently planting the same crop in the same spot every year.
2. Selection of resistant crop: Crop types that are tolerant or resistant to particular protozoan diseases should be chosen and planted. This may be a useful strategy for reducing the damage that infections do to crops.
3. Management of Soil: By managing organic matter, irrigation, and drainage appropriately, you can keep the soil in a healthy state. Certain protozoan infections can be less common in areas with healthy soils.
4. Biocontrolling Agents: To reduce protozoan populations, use biological control techniques such as introducing natural enemies or hostile microbes. Certain helpful microorganisms have the ability to hunt other bacteria or to fight protozoa for nutrients.
5. Quarantine: To stop protozoan infections from entering and spreading to new locations, impose quarantine restrictions. Invasive species and newly developing plant diseases are two situations where this is very crucial.

Importance of Plant Pathology

For a number of reasons, plant pathology is extremely important. Its impact may be seen in many facets of horticulture, agriculture, and ecosystem health. Plant pathology is significant for the following main reasons:

1. Food Security: Food is so important for everyone to survive, so prevention of crop loss by understanding the disease progression is crucial, which results in increased agricultural productivity.
2. Impact on the economy: Every year, it has been noticed that plant diseases result in crop loss, which directly impacts the economy.
3. Conservation of biodiversity: To prevent the loss of biodiversity, it is important to understand the plant-pathogen interaction, thus inhibiting the spread of diseases.
4. Agricultural sustainability: Scientists are developing new strategies for pest management and to use insecticides, pesticides, etc. for sustainable agriculture.
5. Crop Improvement: Gene editing tools are boons to the agricultural industry. Gene editing can make crops resistant to various diseases and pathogens, thus decreasing the use of chemicals.

FAQs – Plant Pathology

1. What is the scope of Plant Pathology?

Plant Pathology is the study of the identification, diagnosis, and treatment of Plant diseases.

2. What is the father of Plant Pathology?

Heinrich Anton de Bary is recognized as both the Father of Mycology and the Father of Plant Pathology (Phytopathology).

3. What is the main field of Plant Pathology?

Plant illnesses produced by bacteria, viruses, nematodes, and other pathogens are the main subject of Plant Pathology, which also focuses on controlling these diseases.

4. What are the factors affecting Plant Pathology?

Environmental factors (temperature, humidity), pathogen features (biology, genetics), and host Plant sensitivity (changing resistance among species) all affect Plant Pathology.

5. Who is the first Indian Plant Pathologist?

Considered the pioneer of Indian Plant pathology, Sir Edwin John Butler made significant advancements in this discipline.