The first natural hybridization was done by Cotton Mather in maize.

Breeding crops with high vitamin, mineral, protein and fat.

Advantage: Polyploidy often exhibit hybrid vigour and increased tolerance to biotic and abiotic stresses.
Disadvantage: Polyploidy results in reduced fertility due to meiotic error resulting in seedless varieties.

Atomic Garden: Is a form of mutation breeding where plants are exposed to radioactive sources typically cobalt-60 or caesium-137 in order to generate desirable mutation in crop plants

UV short waves, X-rays - Physical mutagens.
Nitromethyl, Urea - Chemical mutagens.

Johannsen in 1903 coined the word pureline. It is a collection of plants obtained as a result of repeated self-pollination from a single homozygous individual.

The newly introduced plant has to adapt itself to the new environment. This adjustment or adaptation of the introduced plant in the changed environment is called acclimatization.

Bio-pesticides are biologically based agents used for the control of plant pests. They are in high use due to their non-toxic, cheaper and eco-friendly characteristics as compared to chemical or synthetic pesticides.

Micro organisms are efficient in fixing nitrogen, solubilizing phosphate and decomposing cellulose. They improve soil fertility, plant growth. They are ecofriendly and cost-effective than chemical fertilizers. Example. Azospirillum.

Primary Introduction Secondary Introduction (i) No alternation of genes (i) Alternation by hybridization (ii) Adaptation capability is more (ii) Adaptation capability is more after hybridization