Which one of the following groups of microorganisms is responsible for the plant disease known as "Rust of wheat"?

The correct option is Fungi.

Explanation

Rust of wheat is a significant fungal disease that affects wheat crops globally. It is characterized by the appearance of rust-colored pustules on the stems, leaves, and grains of the plant, which can severely reduce crop yield.

Detailed Analysis:

• Fungi (Correct): The disease "Rust of wheat" is caused by pathogenic fungi belonging to the genus Puccinia. There are three main types of rust affecting wheat:
  • Black Rust (Stem Rust): Caused by Puccinia graminis.
  • Brown Rust (Leaf Rust): Caused by Puccinia triticina.
  • Yellow Rust (Stripe Rust): Caused by Puccinia striiformis.
  These fungi are obligate parasites that require a living host to survive and reproduce.
• Bacteria (Incorrect): While bacteria cause various plant diseases (e.g., Citrus Canker caused by Xanthomonas), they are not responsible for wheat rust.
• Virus (Incorrect): Viruses cause diseases such as Tobacco Mosaic Disease or Yellow Vein Mosaic, but they do not cause fungal rusts.
• Algae (Incorrect): Algae are primarily autotrophic and aquatic. While parasitic algae exist (e.g., Cephaleuros causing Red Rust of Tea), they are not the causative agents of wheat rust.

Key Takeaway:

Rust of wheat is a fungal disease caused by species of the genus Puccinia (e.g., Puccinia graminis).