Breeding of asexual propagated crops are divided into four main groups.
- Flowerless or sterile
- Flowers but rarely set seed
- Normally seeds produce but propagated vegetatively
- Apomicts – reproduce asexually through the process of apomixis.
Breeding methods of asexual propagated plants.
- Clone selection
- Hybridization and Clonal selection.
- Mutation breeding
Clone selection
Clones are always propagated and maintained vegetatively.
steps
- Collection of all clonal variability from local selections, gene banks, commercially grown cultivars.
- Test these clones to disease resistance, yield, abiotic, biotic stress resistance.
- Clones with the desired characters are selected and produce new variety.
Advantages
- Rapid development of the variety compare to the hybridization and selection methods.
- Production permanent hybrid
- Easy to maintenance the variety.
- propagate plants can not do sexual propagation.
Limitation
- Not produce new variability.
- Extreme uniformity and causes susceptibility to epidemics
- Low multiplication ratio (Multiplication ratio number of plant parts or propagules, due to vegetative reproduction plant parts are continuously removed therefore these plants have low multiplication ratio.)
Hybridization and clonal selection
- Hybridized the two different clones (clone A, clone B), then evaluate performance (yield, diseases, biotic stress, abiotic stress) of the progenies with desired characters and select the progeny with the desired and do further testing, regional performance variability and introduce new variety.
Hybridization and clonal selection – Tea Breeding
- First tea breeding was done by clone selection only, then hybridization and clone selection both are used. hybridized to approved clones (these clones should be complement each other with desirable characters.)
- Progeny development through this process are tested for the yield, quality, adaptability, and vegetative propagation ability are tested.
- Best progenies are propagated vegetatively to produce new clones.
Hybridization and clonal selection – Potato Breeding
Potato breeding through vegetative propagation – seed potato.
- Hybridization – Pollen of the male parent is apply to the stigma of the emasculated female plant. Seeds are harvest from the female plants and grown into new plants.
- Selection – plant with desirable characters are selected. (yield, quality, adaptability, and vegetative propagation ability are tested.)
- Clonal propagation : Selected plants are propagated through the plant tubers (Tuber Propagation)
Potato breeding through sexual propagation – true seeds.
Ture seeds are seeds of the F1 hybrid seeds, F1 generations is developed from the crossing two inbred lines
sexual propagated potato vs asexual propagated potato
| sexual propagated potato | asexual propagated potato |
| Transmission of diseases – tuber-borne diseases | Low disease transmission |
| Bulky and heavy | Ease of transport and storage |
Mutation Breeding
Types of mutations
- Point mutations
- Chromosomal aberrations (deletions, duplications, translocations, inversions)
- Ploidy changes (aneuploidy, polyploidy)
- Plastid mutations (variegated or albino plants)
Mutation induction can be occured physically, chemically and callus growth in tissue culture ( somaclonal variation, chromosomal aberrations or point mutations)
In cloning sometimes variations occurred due to genetic mutations E.g. – Mosaics, Sport – a sport or bud sport is a part of a plant that shows morphological differences from the rest of the plant. Sports may differ by foliage shape or color, fruit. Due to genetic mutation. (Sport (Botany) – Wikipedia, 2014)
Phenotypical mutation is important in ornamental plants
References
- Sport (botany) – Wikipedia. (2014, September 1). Sport (Botany) – Wikipedia. https://en.wikipedia.org/wiki/Sport_(botany)