About Lesson
Depending upon the plant pathogen activity, the plant pathogens are classified in to 2 categories
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Active Invaders |
Passive Invaders |
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1. Pathogens which make an aggressive effort to gain entry into intact host cells |
1.No aggressive effort |
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2. They do not require help of any external agency to gain entry into host cells. |
2. Require help of external agencies like insect vectors or wounds caused by agricultural implements. |
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3. Eg. Phyto-pathogenic fungi Phanerogamic parasites |
3. Eg. Plant viruses Phyto-pathogenic bacteria |
- In fungal pathogens, pre-penetration includes spore germination and growth of the resulting germ tube on the surface of the host plant.
- Bacteria have no dormant structures; hence no pre- penetration activity except for multiplication in infection drops on the natural openings.
- However, nematodes show some orientation towards root surface before actual penetration.
- In Rhizoctonia solani, the fungus on coming in contact with root surface, first forms infection cushions and appressoria and from these multiple infections takes place by means of infection pegs.
- In Armillariella mellea, the fungus hyphae form the rhizomorphs (aggregation of hyphae into rope like strands) and only these can cause infection.
Fig : Rhizomorphs
Fig : Appressorium
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