Plant Pathogenic Toxin .They can directly damage plant cells and influence the development and symptoms of plant diseases. PPTX

They can directly damage plant cells and influence the development and symptoms of plant diseases.

1. Plant Pathogenic toxin Pragya Atrey Department of Microbiology

2. Toxin is a  poisonous substance that is a specific product of the metabolic activities of a living organism and is usually very unstable, notably toxic when introduced into the tissues, and typically capable of inducing antibody formation.

3. Classification of Toxins : According to the source of origin, toxins are divided into 3 broad classes namely . Pathotoxins Phytotoxins Vivotoxins

4. Pathotoxins:   These are the toxins, which play a major role in disease production and produce all or most of the symptoms characteristic of the disease in susceptible plants.  Most of these toxins are produced by pathogens during pathogenesis. Ex: Victorian: Cochilobolus victoriae (Helminthosporium victoriae), the causal agent of Victoria blight of oats. This is a host specific toxin.

5. Phytotoxins: These are the substances produced in the host plant due to host- pathogen interactions for which a causal role in disease is merely suspected rather than established. These are the products of parasites, which induce few or none of the symptoms caused by the living pathogen. They are nonspecific and there is no relationship between toxin production and pathogenicity of disease causing agent. Ex: Alternaric acid – Alternaria solani . Piricularin - Pyricularia oryzae .

6. 3. Vivotoxins : These are the substances produced in the infected host by the pathogen and / or its host which functions in the production of the disease, but is not itself the initial inciting agent of the disease. Ex:-Fusaric acid – Wilt causing Fusarium sp.

7. Classification based on  specificity of toxins : Host specific / Host selective toxins: - These are the metabolic products of the pathogens, which are selectively toxic only to the susceptible host of the pathogen. Ex: - Victorin, T-toxin, Phyto-alternarin , Amylovorin . Non-specific/Non-selective toxin: - These are the metabolic products of the pathogen, but do not have host specificity and affect the protoplasm of many unrelated plant species that are normally not infected by the pathogen. Ex: Ten-toxin, Tab-toxin, Fusaric acid, Piricularin , Lycomarasmin and Alternaric acid

8. Host specific Non-host specific Selectively toxic only to susceptible host of the pathogen. No host specificity and can of the also affect the physiology of those plant that are normally not infected by the pathogen. Primary determinants of disease Secondary determinants of disease Produce all the essential symptoms of the disease Produce few or none of the symptoms of the disease. Ex: Victorin, T-toxin Ex: Tentoxin, Tabtoxin Differentiate host –  specific and non-host specific toxins

9. Host specific:-   T toxin-Helminthosporium maydis HC-toxin: Helminthosporium carbonum. HS- toxin: Helminthosporium sacchari. Phytoalternarin : Alternaria kikuchiana PC- toxin: Periconia circinata B. Non-host specific:- Tentoxin: Alternaria tenuis. Tabtoxin or wild fire toxin: Pseudomonas tabaci . Phaseolotoxin : Pseudomonas syringae pv . Phaseolicola .

10. Effect of toxins  on host tissues: 1. Changes in cell wall permeability: Toxins kill plant cells by altering the permeability of plasma membrane, thus permitting loss of water and electrolytes and unrestricted entry of substances including toxins. Cellular transport system, especially, H+ / K+ exchange at the cell membrane is affected. 2. Disruption of normal metabolic functions: Increase in  respiration due to disturbed salt balance. Malfunctioning of enzyme system 3. Other mechanisms: Interfere with the  growth regulatory system of the host plant. Some toxins inhibit root growth. Ex:-Fusarium moniliforme produces a thermostable toxin even in soil around the root, which causes browning of the root and their restricted development.  

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