Desired improved varieties of economically useful crops are raised by

Options

A. Natural selection
B. Hybridisation
C. Mutation
D. Biofertiliser

Answer

**Step-by-Step Solution:**

1. **Understanding the Question:**
The question asks about the methods used to raise desired improved varieties of economically useful crops.

2. **Natural Selection:**
One method is natural selection, where plants that have desirable traits are naturally favored to survive and reproduce. Over time, this leads to the development of improved varieties.

3. **Hybridization:**
Another method is hybridization, which involves crossing two different varieties or species to produce offspring with desirable traits from both parents. This can lead to improved yield, disease resistance, and other beneficial characteristics.

4. **Cross-Hybridization:**
Cross-hybridization is a specific type of hybridization where two different varieties of the same species are crossed. This method is often used to combine the best traits of both parent varieties.

5. **Mutations:**
Mutations can also play a role in developing new varieties. Inducing mutations through chemical or physical means can lead to new traits that may be beneficial for crop improvement.

6. **Chemical Changes:**
Chemical changes, often induced through mutagenesis, can create new genetic variations that can be selected for desirable traits.

7. **Bio-Fertilizers:**
While bio-fertilizers themselves do not directly create new crop varieties, they can enhance the growth of existing varieties, leading to improved yields and better quality crops.

8. **Conclusion:**
In conclusion, desired improved varieties of economically useful crops are raised through methods such as natural selection, hybridization, cross-hybridization, and inducing mutations.

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