Ratoon stunting disease of sugarcane is caused by:

Correct option is C

The correct answer is (C) Bacteria

Explanation:
• Ratoon Stunting Disease (RSD) is one of the most economically significant diseases of sugarcane globally.
• It is caused by the bacterium Leifsonia xyli subsp. xyli (formerly $Clavibacter$ $xyli$).
• It is a xylem-limited bacterium, meaning it lives and multiplies in the water-conducting tissues of the plant.
• The disease results in reduced growth and 'stunting' of the crop, especially in ratoon (second or subsequent) crops, leading to significant yield loss without showing very obvious external symptoms.

Information Booster:
• RSD is primarily spread through contaminated harvesting tools (mechanical transmission).
• Hot Water Treatment (HWT) of sugarcane sets (seed pieces) at 50°C for 2 hours is a common control measure.

Additional Knowledge:
• Sugarcane Mosaic (Option A): Caused by a virus.
• Red Rot (Option B): Caused by the fungus $Colletotrichum$ $falcatum$, arguably the most famous sugarcane disease in India.
• Grassy Shoot Disease: Caused by Phytoplasma (spread by aphids).