Question

Replacing old seeds with new ones is important in maintaining or enhancing the production of a crop. Usually, the higher the seed replacement rate, the better the production. In the case of a hybrid of a crop, the seed replacement rate is -

• A. 25%
• B. 50%
• C. 75%
• D. 100%

Hint:

While self-pollinated crops have an SRR of 25–33% (can be reused for 3–4 seasons), hybrids must be replaced completely every season (100% SRR) to avoid the yield loss and uneven growth caused by $F_2$ genetic segregation.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Seed Replacement Rate (SRR) is the percentage of total cropped area sown with certified/quality seeds instead of farm-saved seeds.
For self-pollinated crops, farmers can save and reuse seeds for a few generations, but for hybrid varieties, the genetic properties change dramatically in subsequent generations.

Step 2: Detailed Explanation:
Hybrid seeds ($F_1$ generation) are produced by crossing two genetically distinct, homozygous inbred parental lines to exploit maximum heterosis (hybrid vigor).
If a farmer saves seeds from a harvested hybrid crop ($F_2$ generation) and sows them in the next season:
- The $F_2$ generation undergoes massive genetic segregation and recombination according to Mendelian laws.
- This segregation leads to a rapid loss of hybrid vigor (typically a 20–30% reduction in yield) and high phenotypic non-uniformity in plant height, maturity, and quality.
- To maintain maximum productivity and uniform crop performance, farmers must buy fresh $F_1$ hybrid seeds from seed producers every single cropping season.
- This means that for any hybrid crop, the required and recommended seed replacement rate is strictly 100%.
Therefore, Option (D) is the correct answer.

Step 3: Final Answer:
The seed replacement rate for a hybrid crop is 100%.