Plant Breeding
The application of art and science to improve plants for human benefit, such as increasing yield, making them more disease-resistant, and improving flavor. this is achieve by control through crossbreeding, genetic engineering, and so many methods.
Crop domestication
Crop domestication is the process that select the wild plant species that contains better suited characters such as easy to growth, diseases resistance cultivate these plants and creating new variety
Natural vs Human of plants selection
Naturally selected plants are evolve naturally, Human selection plants evolve under human influence or under domestication conditions.
In natural selection increases the genetic diversity, human selection cause to reduced the genetic diversity.
There are many characters that have been evolved due to human selection such as
- shattering to non-shattering
- toxic to non-toxic
- tall to dwarf
- Long age to short age
- seedy to seedless
- dormant to non-dormant seed
Human selection is has also resulted in the uniformity of the characters.
- Uniform seed germination
- Uniform maturity time
- Uniform size and shape
Objectives of the plant breeding
- Increased yield – grain yield, fiber yield, latex yield, sugar content.
- Improved quality – grain size, color, cooking time, milling quality
- Disease and pest resistance
- Abiotic stress resistance
- Early maturity
Thing that plant breeders check when selecting for yield in cereals
- Harvest Index – it is the ratio of the total above ground biomass produced by the crops that is useful for consumption to total above-ground biomass produced by the crop. (Grain : straw ratio)
- Grain size and weight – select the large grain for the next generation
- Number of tillers – select the plant that produced more tillers.
- Fertilizer responsiveness – select the plant that more responsive for the fertilizers.
- Pest and diseases resistance – selecting that plants more resistance to pests and diseases.
- Abiotic stress resistance – selecting the plant more resistance to abiotic stress.
Cultivar / Variety
Cultivar is derived from the cultivated variety. which means select the plants that contain desirable trait such as improved yield, disease resistance, bred for make a new variety . Cultivar should be different from already available variety (distinctiveness), phenotypically similar plant within the cultivar(uniformity) and stability
Types of cultivars
- Pure lines
- Hybrids
- Open pollinated populations.
- Clones
Pure lines
Pure lines are made through repeated self fertilization over many generation. these plant are highly homozygous
Hybrids
Produced by crossing inbred plants. highly heterozygous.
Open pollination
These plants are produced through the natural pollination, mainly form the cross pollination. plants have high degree of heterozygosity.
Clones
Produced through the asexual propagation, highly heterozygous genetically uniform and identical to parents.
Inbreeding VS out-breeding
Inbreeding the sexual reproduction within an individual or between closely related individuals, mating the same genotype. Outbreeding is sexual reproduction between genetical dissimilar individuals. inbred plants are genetically uniform and homozygous, outbred plants are genetically variable and heterozygous.
| Inbred plants | Outbred plants |
| sexual reproduction within an individual or between closely related individuals. | sexual reproduction between genetically dissimilar individuals. |
| plant are homozygous | plants are heterozygous |
| genetic uniformity | genetic variability. |
Advantages of inbreeding
- Increases the homozygosity
- Increases the uniformity – useful in large scale agricultural practices.
- Increases the efficiency – more effective when producing uniform plants compared to other methods like outbreeding.
- No need of pollinators.
- Preserves well adapted genotypes.
Disadvantages of the inbreeding
- Inbreeding can lead to inbreeding depression this cause to lower the yields, reduced the growth and development. susceptibility to diseases and pests.
- Limited the genetic diversity – inbred reduced the genetic diversity of the population. since population become less adapted to abiotic stress, diseases and pests.
- increased the expression of the deleterious alleles these alleles are associated with negative characters, such as susceptibility to diseases and pests.
Advantages of outbreeding
- Increased genetic diversity
- Reduced expression of deleterious alleles
- Strong evolutionary potential
- Successful long-term
Disadvantages of outbreeding
- Increased time and cost – relies on effective cross-pollination
- Reduced uniformity – problematic when large scale populations
- Increased the complexity – Produce diverse range of offspring with wide range of characters.