Majority of flowering plants are diploid (2n). The plants which possess more than two sets of chromosome are called polyploids. Polyploidy often exhibit increased hybrid vigour, increased heterozygosity, increase the tolerance to both biotic and abiotic stresses and buffering of deleterious mutations.

The superiority of the F1 hybrid in performance over its parents is called heterosis or hybrid vigour.

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.

Plant breeding is the science of improvement of crop varieties with higher yield, better quality, resistance to diseases and shorter durations which are suitable to particular environment.

Domestication is the process of bringing a plant species under the control of humans and gradually changing it through careful selection, genetic alteration and handling so that it is more useful to people.

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

(i) Hybridization, Mutation breeding, Polyploid breeding, Breeding for developing resistance to diseases, Biofortification, Breeding for resistance to insect pests, New Breeding Techniques (NBT) such as.
(ii) CRISPR/ Cas (Cutting and modifying the genome during the repair process by tool).
(iii) ODM: Oligonucleotide - directed mutagenesis
(iv) Transferring a gene from an identical or closely related species (Cisgenesis).
(v) Organising processes that alter gene activity without altering the DNA itself (Epigenetic methods).

i. Intravarietal hybridization
The cross between the plants of same variety.
ii. Intervarietal hybridization 
The cross between the plants belonging to two different varieties of the same species 
iii. Interspecific hybridization
The cross between the plants belonging to different species belonging to the same genus
Example: Gossypium hirsutum x Gossypium arboretum - Deviraj.
IV. Intergeneric hybridization
The crosses between the plants belonging to two different genera.
Example: Raphanobrassica and Triticale.

i) To increase yield, vigour, and fertility of the crop.
ii) To increase tolerance to environmental condition, salinity, temperature, and drought.
iii) To prevent the premature falling of buds and fruits, etc.
iv) To improve synchronous maturity.
v) To develop resistance to pathogens and pests.
vi) To develop photosensitive and thermos-sensitive varieties.

Green manuring is defined as the growing of green manure crops and use of these crops directly in the field by ploughing. One of the main objectives of the green manuring is to increase the content of nitrogen in the soil. Also, it helps in improving the structure and physical properties of the soil. The most important green manure crops are Crotalaria juncea, Tephrosia purpurea, and Indigofera tinctoria.

(a) Dr. M.S. Swaminathan
(b) C.T. Patel
(c) Dr. B.P. Pal

Euheterosis: True heterosis
(i) Mutational Euheterosis: Simplest type Often lethal, recessive mutant genes from cross pollinated genes.
(ii) Balanced Euheterosis: Well balanced gene combinations, more adaptive to environmental conditions and agricultural.
Pseudo heterosis: Also called luxuriance, has superiority over parents in vegetative growth but not in yield and adaptation, usually sterile or poorly fertile.