Causes of plant disases

here we are going discussing about the causes of the plant diseases and also their brief description

1. Causes of Plant Diseases Lectuer 3 Prepared by R MOHANAPRIYA Assisstant Professor (Plant Pathology) JSA College of Agriculture and Technology, Ma. Podaiyur , Cuddalore district, Tamilnadu

2. Causes of the Plant Diseases Living / Animate / Biotic agents/ Infectious -Eukaryotes -Prokaryotes II. Non-Living / Inanimate / Abiotic agents/ Non Infectious -Deficiencies -Toxicities -Environmental conditions III. Mesobiotic

3. Definition FUNGI Eukaryotic Achlorophyllous Heterotrophic Sexually & Asexually Cell wall – Chitin & Cellulose Eg: Damping off, Downy mildew, Powdery mildew, Rust, Leaf spot, Leaf blight, Smut etc.,

4. PROTOZOA Heterotrophic Animal, fungi, flagellate & plant Eukayrote Motile Microscopic Eg : Club root of cabbage, potato powdery scab

5. CHROMISTA Introduced by Cavalier-Smith , 1981 Means colored Eukaryotic Uni or multi cellular Cellulose Photosynthetic – Chlorophyl C Sexual and asexual Eg : late blight of potato, damping off, & mildew diseases

6. BACTERIA Prokaryotic Unicellular Motile/Non-Motile Microscopic Lacks chlorophyll Rigid cell wall Asexually by binary fission Eg: Bacterial leaf blight of rice, Citrus canker, Apple fire blight etc.,

7. VIRUS Obligate parasite Nucleoproteins RNA / DNA Eg: Cassava mosaic virus, sugarcane mosaic virus, banana bunchy top virus, cauliflower mosaic virus etc., VIROID Naked nucleic acid without protein coat Eg: Potato spindle tuber viroid, coconut cadang cadang viroid disease.

8. PHYTOPLASMA Pleomorphic Lack cell wall Non-Motile Sensitive – Tetracycline & Chloramphenicol Resistant – Penicillin Cannot be culture on artificial media Require sterol Gram negative No spores & flagella. Eg: Sesame phyllody , little leaf of brinjal , sugarcane grassy shoot, rice yellow dwarf etc., SPIROPLASMA Spiral to Helical shape Cell wall less Rotary motility Sensitive – Tetracycline Resistant – Penicillin Can be culture on artificial media Require cholesterol Gram negative No spores & flagella. Eg: Citrus stubborn, corn stunt etc.,

9. Fastidious vascular bacteria / Rickettesia like organism Gram negative Pleomorphic Cell wall Rod shape Cannot be grown in simple culture media Confined to either Xylem or Phloem Eg: Xylem ltd. FVB – Pierce’s disease of grapevine Phloem ltd. FVB – Citrus greening

10. ALGAE Eukaryotic Uni or multi cellular Sexually & Asexually Eg: Red rust of guava, sapoto , mango, and tea. PHANEROGAMIC PARASITE Flowering plants, draw nutrition and water from crop plants Partial / total parasites Partial stem parasite - loranthus Partial root parasite - striga Total stem parasite – cuscuta Total root parasite - orobanche

11. NEMATODES Bilaterally symmetric Ubiquitous Ecto or Endo parasitic Migratory or Sedentary Eg: Wheat ear cockle nematode, rice white tip nematode

12. ABIOTIC DISEASES/ DISORDERS Abiotic disorders are caused by nonliving factors, such as drought stress, sunscald, freeze injury, wind injury, chemical injury, nutrient deficiency, or improper cultural practices, such as overwatering or planting conditions. Zn def. - Khaira disease Ca def. – blossom end rot in tomato & crucifers Boron – top sickness in tobacco & heart rot in sugar beet

13. KOCH’S POSTULATES Must be found associated with every instance Must be isolated and brought into pure culture Healthy host is inoculated with microorganism under optimum condition Must be reisolated and on comparison with original culture, found identical.