Theory:

Diseases caused by microorganism in plants:
1. Citrus Canker
 
Disease-causing organism: Xanthomonas axonopodis (Bacterium)
Canker is mostly caused in citrus plants such as lemon, oranges, and also known as citrus canker.
 
An image of canker disease in lemon caused by a virus shown below.
 
8232130507_09d9804bf6_k.jpg
Canker disease in lemon
 
Mode of transmission:
  • Pathogen entry through plants stomata or wounds on leaves or other green parts.
  • Rain, wind, and polluted equipment can all spread the infection.
Symptoms:
  • Premature fall of leaves
  • Blister-like lesions on leaves, stems and fruits
  • A premature drop of fruits
Treatment:
  • Infected plants or plant parts are burned to stop the disease from spreading.
  • The only way to contain the outbreak is to use disease-free stocks.
  • Infected canker leaves and fruits that have fallen to the ground are gathered and burned.
  • Spraying plants with a \(1%\) Bordeaux mixture are found to be effective.
2. Rust of wheat
 
Disease-causing organism: Puccinia triticina
It causes leaf rust, also known as brown rust. This rust disease can be found in wheat, barley, and other cereal crops.
 
CSIROScienceImage10772Rustaffectedwheatseedlings.jpg
Leaf rust disease in wheat
 
Mode of transmission: Wheat leaf rust spreads through airborne infectious spores.
Symptoms:
  • On the leaf surface, can see dusty, reddish-orange to reddish-brown fruiting bodies.
  •  Small bump like (pustules) structures can see on leaf blades and stems.
  • Patches formed in extreme cases.
How to control:
  • Remove and kill all contaminated pieces, then replant the field with resistant varieties.
  • Applying fungicides early on will help prevent the disease from spreading.
  • Splashing water on the leaves will aid in the spread of rust.
3. Yellow vein mosaic of bhindi or Okra yellow vein mosaic
  
Disease-causing organism: Monopartite Begomovirus
It is also called Bhindi yellow vein mosaic virus that affects okra plants.
 
Bhendi_vein_clearingPhoto-0028.jpg
Yellow vein mosaic of bhindi (Okra)
Mode of transmissionWhite flies are the carriers of the virus.
Symptoms:
  • The characteristic symptom is a yellowing of the entire network of veins in the leaf blade.
  • In severe infections, the plant's younger leaves turn yellow, shrink in size, and become severely stunted.
  • The virus clears the veins of the leaves, and the intervening region becomes entirely yellow or white.
  • The majority of plants in a field may be diseased, and the infection may begin at any stage of plant growth.
  • Infection prevents flowers from blooming, and any fruits that do form are likely to be smaller and harder.
  • Fruits produced by the affected plants are yellow or white and unfit for marketing.
Management measures:
  • Controlling the vectors that transmit Begamo or yellow vein mosaic virusis essential.
  • Disease-affected plants are removed and destroyed from crop fields to prevent secondary disease transmission.
Reference:
https://www.flickr.com/photos/scotnelson/8232130507/in/photostream/
https://upload.wikimedia.org/wikipedia/commons/2/23/CSIRO_ScienceImage_10772_Rustaffected_wheat_seedlings.jpg--
https://upload.wikimedia.org/wikipedia/commons/6/64/Bhendi_vein_clearingPhoto-0028.jpg