1. Selection:
- Selection involves choosing plants with desirable traits and allowing them to reproduce.
- It is a simple and widely used technique for improving crop plants.
- Natural selection, mass selection, and pedigree selection are common methods.

2. Hybridization:
- Hybridization is the crossing of two genetically different plants to obtain offspring with desirable traits.
- It is a powerful tool to introduce new genes into a crop variety.
- Hybrid vigor or heterosis is often observed in the first generation of hybrids.

3. Mutation Breeding:
- Mutation breeding involves the induction of mutations in plants using physical or chemical agents.
- Mutations can lead to the development of new traits or enhance existing ones.
- It is used to create variability and has been successful in developing new crop varieties.

4. Polyploidy:
- Polyploidy is the presence of more than two sets of chromosomes in an organism.
- It can occur naturally or induced through the use of chemicals or other techniques.
- Polyploid plants often exhibit improved traits such as larger flowers, fruits, or increased vigor.

5. Tissue Culture:
- Tissue culture involves the growth of plant cells, tissues, or organs in an artificial medium.
- It allows the production of large numbers of identical plants from a single parent plant.
- Tissue culture has applications in micropropagation, embryo rescue, and somatic hybridization.

6. Genetic Engineering:
- Genetic engineering involves the manipulation of an organism's genetic material to introduce desirable traits.
- It allows for the transfer of specific genes from one organism to another.
- Genetic engineering has been used to develop genetically modified crops with improved traits such as pest resistance or increased yield.

7. Marker-Assisted Selection:
- Marker-assisted selection involves the use of molecular markers to identify and select plants with desired traits.
- It allows for more efficient and precise breeding by selecting plants based on their genetic makeup.
- Marker-assisted selection is widely used in plant breeding programs to improve traits such as disease resistance or quality.

These plant breeding techniques have revolutionized agriculture by providing tools to develop improved crop varieties with higher yield, better resistance to diseases and pests, and enhanced nutritional content. Familiarity with these techniques and their applications is essential for candidates appearing for the UPSC Botany Optional Paper II.