Plant Pathology Module 7
Pathogen & Disease Relationships
|
Disease |
Causal Organism |
Type |
|
Late blight of potato |
Phytophthora infestans |
Fungus |
|
Wart disease of potato |
Synchytrium endobioticum |
Fungus |
|
Club root of cauliflower |
Plasmodiophora brassicae |
Protist |
|
Brown spot of rice |
Helminthosporium oryzae |
Fungus |
|
White rust of crucifers |
Albugo candida |
Fungus |
|
Downy mildew of bajra |
Sclerospora graminicola |
Fungus |
|
Black rust of wheat |
Puccinia graminis tritici |
Fungus |
|
Purple blotch of onion |
Alternaria porri |
Fungus |
|
Red rot of sugarcane |
Colletotrichum falcatum |
Fungus |
|
Pineapple disease of sugarcane |
Ceratocystis paradoxa |
Fungus |
|
Moko disease of banana |
Pseudomonas solanacearum |
Bacterium |
|
Bunchy top of banana |
BBTV (Banana Bunchy Top Virus) |
Virus |
|
Coffee rust (Sri Lanka, 1867) |
Hemileia vastatrix |
Fungus |
Viruses, Viroids, and Prions
- Most plant viruses: ssRNA (+) type (≈78%)
- Largest family of plant viruses: Potyviridae
- Papaya mosaic disease: Viral
- Cauliflower mosaic virus: dsDNA
- Potato leaf roll virus vector: Aphids
- Common vectors of plant viruses: Aphids (most), whiteflies, leafhoppers
- Prions: Infectious protein particles without nucleic acid
Bacteria and Mycoplasma
- Mycoplasma sensitive to: Tetracycline
- MLOs (Mycoplasma-Like Organisms): No cell wall; spiral forms called Spiroplasma
- First bacterial plant disease: Fire blight of pear (Erwinia amylovora)
- Crown gall disease: Agrobacterium tumefaciens
- Ratoon stunting of sugarcane: Clavibacter xyli
- Agrobacterium-mediated gene transfer effective in: Dicots
Fungal Biology
- Order of Downy Mildew fungi: Peronosporales
- Order of Smut fungi: Ustilaginales
- Repeating spores in rust fungi: Uredospores (n+n, dikaryotic)
- Sexual spores in downy mildew: Oospores (2n, diploid)
- Ergot sclerotia: Resting mycelial structures
- Most poisonous mushroom: Amanita phalloides
Important Concepts & Definitions
- Inoculum: Infective unit that can cause infection (e.g., spores, sclerotia).
- Infection: Establishment of pathogen after penetration.
- Invasion: Spread of pathogen inside the host.
- Incubation period: Time from infection to symptom appearance.
- Syndrome: Sum total of all symptoms and signs.
- Pathogenesis: Chain of metabolic events causing disease.
- Pathogenicity: Ability of a pathogen to cause disease.
- Virulence: Degree of pathogenicity of an organism.
- Virion: Virus particle (nucleic acid + capsid).
- Disease potential: Ability of a host to contract disease.
- Cybrid: Cell with nucleus of one parent and cytoplasm of both parents.
Host Resistance and Control
- Vertical Resistance: Major gene / Qualitative / Race-specific resistance
- Horizontal Resistance: Polygenic / Quantitative / Non-race-specific
- Loose smut of wheat: Internally seed-borne
- Blast disease in rice reduced by: Silicon application
- Fusarium causes: Mango malformation
- Pseudomonas fluorescens: Used in biological control
Miscellaneous
- Agar-agar source: Gelidium amansii (Red seaweed)
- Endemic region for wart disease of potato in India: Darjeeling Hills (West Bengal)
- Coffee rust outbreak year: 1867 (Sri Lanka)
