Fundamentals of plant pathology

Basics of plant pathology, plant disease epidemics, important terminologies and pathogenicity is explained briefly.

1. Fundamentals of PLANT PATHOLOGY D r Bhagyashree Khamari Assistant Professor Department of Plant Pathology Institute of Agricultural Sciences Siksha o Anusandhan (Deemed to be University) Bhubaneswar, Odisha

2. Loss of quality and q uant ity of product Loss of a esthetic value C hange in crop system Increase in cost of production Change in food habit Loss of e mployment Destroy a gricultural industries Affect International trade Importance of Plant disease

3. Important plant disease Epidemics Irish Famine – 1845 (Late blight of Potato) Coffee rust in Sri lanka (1870) Bengal famine (1943) Brown spot of rice

4. Other Famines Wheat rust epidemics occurred from time to time in many countries which forced farmers to change their cropping pattern from wheat to corn. Powdery mildew of grapevines caused by Uncinula necator in 1854 which reduced the French wine production by 80 per cent. In 1878, the downy mildew of grapes caused by Plasmopara viticola ultimately led to the discovery of Bordeaux mixture.

5. Earlier Concepts regarding cause of Plant diseases: Jews – regarded that disease is due to a nger of God. Yunani – worshiped Suryanarayan for protecting their crops from diseases. Roman – Roman worship Robigo and Robigu s (Rust God and G oddess respectively) and celebrated “ Rubigalia ” festival for protecting their crops from rust

6. What is Plant Pathology? Phytopathology (Phyton : plant) Greek - Pathos (suffering) + Logos (study) = The study of the suffering plant Plant pathology is that branch of agricultural, botanical or biological sciences which deals with the study of: cause of the disease Resulting losses and Control of plant diseases

7. OBJECTIVES OF PLANT PATHOLOGY To study the biotic, abiotic and environmental causes of plant diseases. To study the mechanism of disease development. To study the interaction between plant and pathogen in relation to environmental conditions . T o d e v e lop th e m e t hod s of p lant d i se a se management .

8. Disease:   It is a malfunctioning that is caused by continuous irritation by biotic and abiotic factors resulting in production of symptoms. Disorder or physiological disorders .   The diseases caused by abiotic factors such as the deficiency of nutrients or unfavourable environmental condition.

9. Pathogen :  Disease causing organisms are known as pathogen. Pathogenicity   : It is the ability of a pathogen to cause disease under a given set of environmental conditions. Virulence   : It is a measure or degree of pathogenicity. Aggressiveness: It  is capacity of a pathogen to invade and grow in the host plant and to reproduce on or in it. Pathogenesis or disease cycle   : It is the chain of events that leads to development of a disease in the host .

10. Parasite :  Organisms which depends on other organism (the host) for their food and shelter. All the pathogens are parasites but all the parasites are not pathogens . Biotrophs   or obligate parasites : organisms which obtain their food from living tissues where it completes its life cycle . e.g., rusts, smuts, powdery mildews etc . Facultative parasite: Organism which are generally saprophyte but occasionally under favourable condition behaves as parasite.

11. Saprophytes/saprobes : Organisms which live and derive their nutrition from the dead and decay organic matter. Facultative saprophytes or hemibiotrophs : Organism that are generally parasite but under certain unfavorable condition behaves as saprophyte. Necrotroph or perthotroph or perthophytes : A parasite   when kills the host tissue in advance of  entry  and then lives saprophytically , e.g. Sclerotium rolfsii and Pythium species.

12. Infection  is the establishment of the parasitic relationship between the pathogen and host after entry. Incubation period  is the period between pathogen entry  and development of the disease symptoms. Invasion and colonization  is the growth and multiplication of the pathogen through the tissue of the host varying extent . Latent infection : When the host is infected by pathogen but doesn’t express any symptom.

13. Host Host Primary inoculum Primary infection Secondary inoculum Secondary infection

14. Inoculum : Pathogen or its part which cause infection. Inoculum potential : It is the minimum amount of inoculum to cause infection. Primary inoculum: The dormant pathogen or its spores which initiates infection (Primary infection). Secondary inoculum : Pathogen or its spore produced primary infection and cause secondary infection. Inoculation: It is the process of transferring pathogen to a host. Isolation : It is the process of separation of pathogen from its host and culture in nutrient media.

15. Epiphytotic : Organism growing on the surface of plant Endophytic : Organism growing inside the plant Phylloplane : on the surface of leaf Phyllosphere : area surrounding the leaf Rhizoplane : on the surface of root Rhizosphere : Area around the root Predisposition: It is the set of conditions that makes the plant vulnerable to the attack of a pathogen.

16. Phyllosphere Rhizosphere

17. Pathogenicity: Ability of an organism to cause disease. Koch’s Postulate (By Robert koch ) The microorganism must be found in diseased but not healthy individuals The microorganism must be cultured from the diseased individual. Inoculation of a healthy individual with the cultured microorganism must recapitulated the disease. The microorganism must be re-isolated from the inoculated, diseased individual and matched to the original microorganism. 

18. Steps to prove that the organism from infected plant tissue caused the original infection. ( A) Isolation of pathogen from infected tissue . (B) Inoculation in susceptible host (C) Re-isolate the pathogen form the susceptible host and examine in microscope . (D) Comparison between isolated and reisolated pathogen.

19. Exceptions to Koch’s Postulates Microorganisms that are unable to cultured on artificial media . When 2 or more organism work in synergy to cause a disease. Symptoms or diseases that can be caused by several microbes. Highly contagious, virulent, or dangerous strains We obviously do not want to create more of a dangerous disease.

20. Thank you