Plant Disease Signs and Diagnosis

Study Notes

Signs of Plant Diseases

Signs refer to structures of pathogens associated with infected plant parts, such as fungal mycelia, spores, and fruiting bodies.
Other signs include bacterial ooze, virus particles, sclerotial bodies, and nematodes at various developmental stages.

Plant Disease Diagnosis

Diagnosis is the identification of diseases through characteristic symptoms and signs.
Koch's postulates are used for confirming pathogenecity, consisting of a series of steps:
- The suspected pathogen must be present in the diseased plant.
- The pathogen must be isolated and grown in pure culture.
- Symptoms of the disease must appear when the cultured pathogen is inoculated into a healthy plant.
- The organism must be re-isolated from the inoculated plant, identical to the original.

Classification of Plant Diseases

Plant diseases can be classified based on the affected plant organ, such as:
- Root diseases
- Foliage diseases
- Fruit diseases
- Stem diseases
They can also be classified according to symptoms, including:
- Leaf spots
- Rusts
- Smuts
- Anthracnose
- Mosaics
- Wilts
- Fruit rots
Diseases can also be classified by the type of affected plants:
- Vegetable diseases
- Forest tree diseases
- Field crop diseases
- Ornamental plant diseases

Halophiles

Halophiles are phototrophic organisms that utilize bacteriorhodopsin, a purple form of chlorophyll.
They thrive in extreme salinity, like that found in the Great Salt Lake and Dead Sea.
Can survive in alkaline environments with pH levels up to 11.5.
Most halophiles are aerobes, requiring oxygen for survival.

Methanogens

Methanogens are anaerobic organisms that decompose organic matter, producing water and methane gas.
They utilize carbon dioxide to generate methane, a key flammable component of natural gas.

Parasitic Flowering Plants (Phanerogams)

More than 2500 higher plants exhibit varying degrees of parasitism on other plants.
Only a select few cause significant damage to crops or forest trees.
- Hemi-parasites: Depend on hosts for water and minerals but can photosynthesize, e.g., Striga asiatica (witch weed) and Phorandendron spp. (true mistletoes).
- True parasites:
  - Cuscuta spp. (dodder) forms yellow to orange leafless vines on host plants.
  - Orobanche spp. (broomrapes) emerge as clusters of stems from the soil, displaying yellowish, brownish, or purplish colors at the base of host plants.

Description

Explore the signs of plant diseases such as fungal mycelia, spores, bacterial ooze, and more, found associated with infected plant parts. Learn about plant disease diagnosis and identifying diseases through characteristic symptoms. This quiz covers the structure of pathogens and methods for disease identification in plants.