Question

When farmers of a particular region were concerned that pre-mature yellowing of leaves of a pulse crop might cause decrease in the yield. Which treatment could be most beneficial to obtain maximum seed yield in pulse crop

• A. Application of iron and magnesium to promote synthesis of chlorophyll content
• B. Frequent irrigation of the crop
• C. Treatment of the plants with cytokinins along with a small dose of nitrogenous fertilizer
• D. Removal of all yellow leaves and spraying the remaining green leaves with 2, 4, 5 trichlorophenoxy acetic acid

Hint:

Remember the Richmond-Lang Effect: Cytokinins delay senescence by preventing chlorophyll breakdown and mobilizing nutrients toward the leaves. This is a common topic in plant physiology exams.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Premature yellowing of leaves is a sign of leaf senescence, which leads to chlorophyll degradation, reduced photosynthesis, and lower crop yields. Plant hormones and key nutrients can be used to delay this process.

Step 2: Detailed Explanation:
Let us analyze the physiological treatments for leaf yellowing:

Cytokinins are plant growth regulators that delay leaf senescence (the Richmond-Lang effect). They preserve chlorophyll, maintain cellular proteins, and promote nutrient mobilization toward treated leaves, keeping them green and photosynthetically active for a longer duration.

For a pulse crop (legume), nitrogen is essential for protein synthesis and grain development. Although legumes fix nitrogen symbiotically, premature yellowing often indicates a temporary nitrogen deficiency due to inefficient root nodules or high reproductive demand.

Applying a small starter dose of nitrogenous fertilizer along with cytokinins provides the raw material needed for protein synthesis, while the hormone maintains photosynthetic activity, directly improving seed yield.

Let us evaluate the other options:
-Option (A): While Fe and Mg are structural components of chlorophyll, applying them will not resolve leaf yellowing if it is caused by hormone-driven senescence or nitrogen deficiency.
-Option (B): Frequent irrigation does not directly address nutrient-driven senescence and can cause waterlogging.
-Option (D): Removing leaves reduces the plant's photosynthetic area, and applying 2,4,5-T (a synthetic auxin/herbicide) is toxic and would harm the crop.
Therefore, treatment with cytokinins and nitrogen is the most beneficial approach.

Step 2: Final Answer:
The correct option is (C).