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Plant Pathology 

 Plant pathology or phytopathology is the science, which deals with the plant diseases.

 The term plant pathology or Phytopathology has been derived from three Greek  Phyton = plant  Pathos = ailments/suffering/disease  Logos = discourse/knowledge/Study

 Plant pathology is the branch of agricultural, botanical or biological science which deals with the causes, etiology (aetiology), resulting in losses and management methods of plant diseases.

Science and Art

 Concept of Disease

  The term disease is derived from French word 

• Dis = nothing

 • Ease = comfortable (lack of comfort) 

 Plant disease is a malfuntioning process in plant body caused by continuous irritation by some agents (plant pathogen) which results in some suffering or symptoms production.

 Plant disease is any abnormal condition that alters the appearance or function of a plant.

 Disease may also reduce yield and quality of harvested product.

What is Pathogen ?

Patho = Disease

 Gen = Generating

Any agent or entity which can induce disease in plants. Eg.-Fungi, Bacteria, Virus, Vivoids, Mollicutes.

How pathogen affect plants

1) By utilizing host cell contents. 

2) By killing host through their enzyme, toxins etc.

 3) By weakening the host.

Scope of Plant Pathology :-

 Study of etiology, symptoms, predisposing factors and recurrence of such diseases. 

 Plant pathology deals with different aspects of plant diseases.

 The branch focuses on understanding how hosts, pathogens, and environments interact to cause plant diseases and on understanding how to control plant diseases.

Objectives of Plant Pathology 

The science of plant pathology has four main objectives: 

1. To study living, non-living and environmental causes of diseases or disorders of the plants. (Etiology)

 2. To study the mechanism of plant disease development. (Pathogensis)

 3. To study interaction between host/susceptible and the pathogens. (Epidemiology)

 4. To develop systems of management of plant diseases and reducing losses caused by them. (control).

 In 1845 “Irish famine” the late blight of potato caused by “Phytophthora intestans”. 

 In 1842-43 “Bengal famine” the “Leaf spot of Rice” caused by “Helminthosposium oryzai”.

History of Plant Pathology with special reference

1. Dutch worker Leeuwenhock (1675) invented the microscope and through it observed and first described bacteria in 1683. (father of microbiology).
2.  Prevost (1755-1819) - he proved that bunt of wheat caused by a fungus.
3. E.J. Bulter who is also known as the ‘Father of Plant Pathology’.  d a classic text book, ‘Fungi and Diseases in Plants’ in 1918.
4.  Anton de-Barry (1831-1888) worked on Late blight disease of Potato “Father of Modern Plant Pathology”.
5. Prof. P.A. Millardet (1882) of France discovered Bordeaux mixture for the control of ‘Late blight of Potato’ and ‘Downey mildew disease of grapes.’ 
6. B.B. Mundkur started work on control of cotton wilt through varietal resistance. ‘Indian Phyto pathological Society’. a text book entitled, ‘Fungi and Plant Diseases’.
7. M.K. Patel (Father of Indian plant bacteriology)
8.  Yeshwant Laxman Nene reported “Khaira” disease of rice. authored the book "Fungicides in Plant Disease Control“ 
9. Dr. Karam Chand Mehta (Father of Indian Rust)  investigated the life cycle of cereal rusts in India. Wrote monograph on "Further studies on cereal rust in India''. 
10.   S N Das Gupta carried studies on black tip of mango. 
11. A. Mahadevan wrote the book ''Microorganism in Diseased Plants“. 
12. CD Mayee  Wrote 'Phytopathometery'. 
13. RS Singh Wrote ''Plant diseases", a book known as ‘Bible of Plant Pathology’. 

Terms and Concepts in Plant Pathology 

 Disease: 

Any malfunctioning of host cells and tissues that result from continuous irritation by a pathogenic agent or environmental

 Disorder:

 The diseases caused by the deficiency of nutrients or unfavourable environmental factors are sometimes termed as disorders or physiological disorders.

 Pathogen: 

An entity, usually a micro-organism that can incite disease. agent that causes pathos (ailment, suffering) or damage.

 Host: 

An organisms which provide shelter and nourishment to another living organism.

 Pathogenesis: 

    this is the process or chain of events where by disease development takes place. 

 Parasite: 

    Organisms which derive the materials they need for growth from living plants (host) are called parasites. 

 Obligate parasite

:     A organisms which derived nutrient only from living organisms/host. Ex- rust, powdery mildew and downey mildew. 

  Facultative parasite:

     An organism that is usually saprophyte but under certain conditions can uptake nutrient from living organism. Ex- rhizopus.

  Obligate saprophyte: 

            A organisms which derived nutrient only from dead materials (saprophyte). Ex- pilobolus spp

 Hypertrophy: 

                Excessive growth due to increase in size of cells.

  Hypersenstivity: 

                Excessive sensitivity of plant tissues to certain pathogens. affected cells are killed quickly,

 Blight:

        Burning appearance of a plant all in parts or its organs such as leaf, twig, stem & other Arial parts of the host is called blight.

 Early blight- when blight stand from mid of leaf. Ex- ‘early blight of potato (Alternaria solani)’. 

 Late blight- when blight stand from margin of leaf. Ex- ‘late blight of potato (Phytophthora infestans)’.

 Latent virus: A virus that does not induce symptoms in its host. 

 Latent infection: The stage in which a host is infected with a pathogen but does not show any symptoms. 

 Saprophyte: In organism which lives on dead and decaying organic matter.

  Susceptibility: The inability of a plant to resist the effect of a pathogen. 

 Susceptible: A plant or species which is incapable of resisting the effect of a pathogen. 

 Resistance: The ability of an organism to overcome, completely or partially the effect of a pathogen.

 Infection: Establishment of the pathogen in the host. 

 Infections disease: A disease caused by a pathogen which can spread from a diseased to a healthy plant.

Pathogenesis:

 Pathogenesis is a series of events that happened in succession during a pathogenic relationship of a pathogen and host which leads to disease, refers to the origin, development and resultant effects of disease from the initial appearance of disease. 

The term pathogenesis comes from Greek word for ‘disease’ and ‘beginning’. The study of pathogenesis is important to diagnose and manage diseases. 

Causes / factors affecting Disease development

 Causes of plant diseases 

 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.

 

1.  Abiotic (Inanimate) factors

  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).

II. Mesobiotic causes 

  These are the disease incitants which are neither living nor non-living.

 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.

 Biotic (Animate) causes 

 This category includes the pathogens which are animate or living or cellular organisms. They are: 

1) Prokaryotes like bacteria

2) Eukaryotes are the organisms with true nucleus.

     i) Fungi: 

    ii Protozoa 

    iii) Algae 

Disease triangle

 The interaction of host, pathogen and environment results in disease development. It is generally illustrated by a triangle, also called a disease triangle. 

Disease Development in Plant Population

1.Host: 

2.Pathogen:

 3.Environment: 

. 4.Time: 

Disease cycle

 The chain of events involved in disease development including the stages of development of pathogen & effect of the disease on the host. Steps is disease cycle There are five steps of disease cycle as given below

1. Inoculation The arrival / transfer of a pathogen on to a host is called inoculation.

 2. Penetration The initial invation by a pathogen on to a host. Entry of pathogen inside / within the host is known as penetration. 

3. Infection :-   Entry and establishment of a pathogen inside / within the host is known as infection. 

4. Invation Spread of pathogen within the host is known as invation. 

5. Growth & reproduction 

  Growth refers to irreversible change in body / structure of pathogen.

Classification of plant diseases: 

Disease can be classified by many ways some are given below

1. Based on extent to which disease is associated. 

2. Based on types of crop. 

3. Based on infected plant part.

 4. Based on natural perpetuation and mode of infection. 

5. Based on transmission. 

6. Based on types of symptoms. 

7. Based on severity of disease/occurrence of disease.

 8. Based on causal organism.

 9. Based on cause of plant disease.

1. FUNGI 

1) Fungi are eukaryotic, Achlorophyllous organisms that may reproduce sexually and asexually and whose filamentous branched somatic structures are typically surrounded by cell walls containing chitin or cellulose.

 Fungi are

2) Eukaryotic cells 

3) Achlorophyllous(lack chlorophyll pigments.

4) Flamentous branched somatic structures and multi-cellular microorganism,

 5) Cell wall mainly composed of carbohydrates namely chitin

6) Reproduction by both sexually and asexually. Both sexual and asexual reproduction often results in production of spores.

8) Habitate may be free-living as saprophytes

9) All are heterotrophic - They are heterotrophs that acquire nutrients by absorption.

10.Type of nutrition  Mostly saprophytic (they absorb soluble organic food), they are grow on dead & decaying materials like- tree bark, dung, wood .

11) Parasitic - absorb nutrients from cells of living hosts (plants & animals).

12). Hyphae is a tubular, transparent filament, usually branched, composed of an outer cell wall . Hyphae are divided into compartments or cells by cross walls called septa and are generally called as septate (with cross wall). 

13. The hyphal mass or network of hyphae constituting the body (thallus) of the fungus is called as mycelium

Virus 

contains DNA or RNA as genetic material and a protein coat, whereas 

viroids

 have no protein coat, but only RNA as their nucleic acid. 

This is the reason why viroids are carried inside viruses. e.g., hepatitis-D is a viroid that is carried in the capsid of hepatitis-B virus.

 Algae: Algae are eukaryotic, unicellular or multicellular organisms and mostly occur in aquatic environments.

They contain chlorophyll and are photosynthetic.

 They reproduce by asexual and sexual processes. 

The study of algae is called phycology or algology

Name of the diseases Causal organism                         Name of the diseases Causal organism 

Late blight of potato                                                     Phytophthora infestans 

Rice blast disease                                                         Pyricularia grisea 

Brown spot of rice                                                        Dreschlera oryzae 

Coffee rust                                                                    Haemilea vestarix 

Downy mildew of grapes                                             Plasmopara viticola 

Rust of wheat                                                                 Puccinia graminis tritici