Types and processes of Artificial Hybridization
Artificial hybridization is the process in which only desired pollen grains are used for pollination and fertilization.
Pollination is the process of reproduction in plants in which plants transfer pollen grains from another to stigma. Pollination can be of two types:
Cross-pollination
Self-pollination
Cross-pollination is the process when one plant pollinates a plant of another variety. The genetic material of two plants combine and the resulting seed from that pollination will have features of both varieties and a new variety will come out. Sometimes this method of cross-pollinating is intentionally used in the garden to create new varieties.
Self Pollination can be defined as the transfer of pollen from the anther of a flower to the stigma of the same flower or sometimes to that of a genetically identical flower.
For successful pollination to occur, pollen and stigma should be compatible. Incompatibility may lead to the rejection of pollen grains. This situation is undesirable, especially in commercial crop production. Therefore, artificial hybridization was developed.
Artificial Hybridization
Pollen-stigma compatibility is essential for successful pollination and fertilization. Once compatible pollen is accepted by pistil, events of fertilization proceed, whereas incompatible pollen will be rejected. This interaction where a pistol is able to recognize its pollen is the result of the long-term pollen-pistil interaction and the release of chemicals by pollen.
It is very important to understand how pollen-pistil interaction takes place in hybridization as it is one of the innovative methods of the crop production improvement program. Only the desired pollen grains are made to introduce to the stigma through pollination during the process of artificial hybridization. This process helps to avoid unwanted pollen rejection and saves time. This process helps to grow plants with the desired characteristics.
Steps in Artificial Hybridization
Hybridization involves two steps:
Emasculation
Bagging
Emasculation
We know hybridization is the method of selective breeding. Thus, before the anthers could release pollen grains, they need to be thrown off. This step of removal of another using forceps is termed emasculation. In the case of unisexual flowers, this step is not necessary.
Bagging
Bagging is the protection of emasculated flowers from contamination by undesirable pollen grains. Here, the flower is covered in a bag, still, the flower attains receptivity. Bagging is done before the flowers are open in unisexual flowers. A female flower is completely protected from contamination by the process of emasculation and bagging. Once the flower attains stigma receptivity, the desired pollens are dusted on the stigma. This is resealed for further developments.
Hence, artificial hybridization ensures that the right type of pollen has been transferred to the stigma of the flower. In addition, the chance of fertilization is high. Through this approach, a variety of strains of crops can be developed and it improves the quality of crops with desirable characteristics.
FAQs on Artificial Hybridization in Plants
1. What is meant by artificial hybridization in the context of plant breeding?
Artificial hybridization is a controlled plant reproduction technique used in crop improvement programs. It involves intentionally crossing two different plant varieties, species, or genera that possess distinct desirable traits. The primary goal is to combine these traits into a single, superior offspring or 'hybrid'. This is achieved by ensuring that only desired pollen grains are used for pollinating a specific stigma, preventing any unwanted pollination.
2. What are the two primary steps involved in performing artificial hybridization?
The two fundamental steps in artificial hybridization are:
- Emasculation: This is the removal of anthers or stamens from a bisexual flower before they mature and release pollen. This prevents self-pollination.
- Bagging: After emasculation (or for a selected female flower), the stigma is protected from contamination by unwanted pollen by covering it with a bag, usually made of butter paper. Once the stigma is receptive, desired pollen is dusted onto it, and the flower is re-bagged.
3. Why is emasculation a crucial step for bisexual flowers in artificial hybridization?
Emasculation is crucial for bisexual flowers because they contain both male (anthers) and female (pistil) reproductive parts. Without removing the anthers, the flower would likely self-pollinate. This would defeat the purpose of hybridization, which is to introduce pollen from a different, specifically chosen parent plant. Therefore, emasculation ensures the stigma is only fertilised by the desired pollen grains selected by the plant breeder.
4. What is the main purpose of bagging a flower after emasculation?
The main purpose of bagging is to prevent contamination of the stigma. After emasculation, the stigma is exposed and vulnerable to pollination by any unwanted pollen carried by wind, insects, or other agents. Covering the flower with a bag creates a physical barrier, ensuring that the stigma remains unpollinated until the breeder is ready to introduce the pollen from the desired male parent. It guarantees the integrity of the cross-breeding experiment.
5. How has artificial hybridization been used to improve crop varieties? Provide examples.
Artificial hybridization is a cornerstone of modern agriculture and the Green Revolution. It helps create new crop varieties by combining desirable characteristics from two different parents. For example, breeders can cross a high-yielding but disease-susceptible wheat variety with a lower-yielding but disease-resistant variety. The goal is to produce a hybrid that is both high-yielding and disease-resistant. Many modern varieties of wheat, rice, and maize are products of this technique.
6. What happens if incompatible pollen lands on the stigma during artificial hybridization?
If incompatible pollen—pollen from the wrong species or a genetically incompatible plant—lands on the stigma, fertilization will typically not occur. The pistil has a natural recognition mechanism, often called pollen-pistil interaction, which allows it to accept compatible pollen and reject incompatible pollen. This rejection can happen at several stages: the pollen grain may fail to germinate, or the pollen tube growth may be inhibited in the style. This natural barrier ensures that only appropriate genetic crosses succeed.
7. Is emasculation necessary for unisexual female flowers in hybridization experiments?
No, emasculation is not necessary for unisexual female flowers (pistillate flowers) in hybridization experiments. Since these flowers only contain the female reproductive parts (pistil) and lack the male parts (stamens), there is no risk of self-pollination. Therefore, the plant breeder can skip the emasculation step and proceed directly to bagging the flower bud to prevent contamination from unwanted pollen before the stigma becomes receptive.
