Question

Brown leaf spot on paddy is caused by the deficiency of

• A. Zn
• B. Fe
• C. Cu
• D. Mo

Hint:

Khaira disease of rice is a classic exam question; it is caused by Zinc (Zn) deficiency and can be cured by spraying zinc sulfate (\(\text{ZnSO}_4\)) mixed with lime.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Nutritional disorders in paddy (rice) are common in various soil types and significantly affect crop yields.
A well-known physiological disorder in rice characterized by the appearance of brown, rust-colored spots on the leaves is Khaira disease, which is caused by the deficiency of zinc (Zn).
Detailed Explanation:
Zinc is an essential micronutrient required by plants for various enzymatic activities, hormone regulation (especially auxin synthesis), and protein synthesis.
When paddy fields are deficient in zinc, typically under calcareous, waterlogged, or sandy soils with high pH, plants exhibit characteristic deficiency symptoms.
These symptoms, known as Khaira disease (first discovered by Dr. Y. L. Nene in Pantnagar, India), typically appear 10 to 15 days after transplanting.
The lower leaves develop chlorotic areas that rapidly turn into brown, bronze, or rust-colored spots.
These spots eventually coalesce, covering entire leaf blades and causing them to dry up.
This condition is often referred to as brown leaf spot or bronzing of paddy due to nutrient deficiency, distinguishing it from the fungal brown spot disease caused by Bipolaris oryzae.
Therefore, zinc deficiency is the primary cause of these physiological brown spots on paddy.

Step 2: Final Answer:
The brown leaf spot/bronzing (Khaira) on paddy is caused by the deficiency of Zn.