What is Apomixis?
Apomixis can be defined as a means of asexual reproduction where fertilisation. The term was first coined by botanist Hans Winkler. The seed of a plant is developed without fertilisation.
Apomixis is the process of identifying and developing diploid embryos or seeds found in a plant without fertilization or the term Apomixis can also be explained as a form of asexual reproduction that occurs via seeds, in which embryos develop without fertilization that occurs naturally in other plants.
Apomixis is also known as asexual seed formation which is obtained as the result of a plant gaining the ability to the most important process through bypassing the most fundamental and basic aspects of sexual reproduction, meiosis, and fertilization. Without the requirement for male fertilization, the resulting seed germinates a plant that develops which will be as exactly as a maternal clone.
What Are The Characteristics of Apomixis?
The characteristics of Apomixis are:
It is an asexual means of plant reproduction and is found in many species especially in fruit crops.
The process does not involve the union of male and female gametes and therefore there is no genetic recombination. Apomixis does not lead to the generation of variability in a population.
Apomixis does not permit gene flow which means it does not permit the combination of genes from different sources.
It helps in the rapid development of pure lines and can be achieved by haploid parthenogenesis.
Apomixis can be genetically controlled and is useful in conserving superior genotypes and hybrid vigor.
It has been reported in more than 300 plant species of 35 families.
Apomixis Classification
Apomixis can be classified based on:
Cell involved
Occurrence
Frequency
Apomixis Types:
Apomixis Examples:
Apomixis can be observed in hawthorns, shadbush, Sorbus, brambles, and blackberries, meadow grasses, mat grass, hawkweeds, etc.
Applications of Apomixis
Apomixis has many applications in the produce sector. Some of them are explained below:
Development of Pure Lines: Apomixis is a means of rapid production of pure lines in plants. Haploid apogamy and parthenogenesis give rise to haploid plants which after being treated by colchicine treatment can produce diploid pure lines. These pure lines can be used in the production of high yielding cultivars and hybrids.
Maintenance of Purity: Obligate apomixis breeds retain the characteristics of the mother plant which are useful in maintaining genetic purity from generation to generation. It can maintain a genotype for several generations.
Conservation of Heterosis: Obligate recurrent apomixis is useful in conserving hybrid vigor for numerous generations. As apomixis does not permit segregation, heterosis can be easily conserved.
Easy Hybrid Seed Production: Apomixis offers a simple way of hybrid seed production. These seeds are automatically produced by apomictic means and there is no need for crossing. Once a hybrid is developed using an apomictic line as one of the parents, the hybrid seed production will occur automatically. It is also more affordable than conventional methods of hybrid seed production.
Advantages of Apomixis:
Apomictic plants conserve the genetic structure of their carriers which enables them to maintain heterozygote advantages for many generations. It offers a great advantage in plant breeding where genetic uniformity is maintained for both homo and heterozygosity. The advantages of apomixis are:
Rapid multiplication of genetically uniform progenies without the risk of segregation.
Hybrid vigor or heterosis can be fixed permanently in crop plants.
If maternal characteristics are present in resultant progenies then it can be exploited from generation to generation.
The significance of Apomixis
The significance or the importance of apomixis in the plant breeding industry is massive. It is a method that develops seeds without fertilization. It can be referred to as a means of asexual reproduction which mimics sexual reproduction. It helps in the production of hybrid seeds and is cost-efficient when it comes to large-scale production. There is an increase in yield as well. Also, since there is no cross-fertilization, apomixis helps in preserving the good characteristics of a crop plant.
FAQs on Apomixis
1. What is apomixis in plants, and how does it relate to sexual reproduction?
Apomixis is a unique form of asexual reproduction in plants that mimics sexual reproduction by producing seeds without fertilisation. Essentially, the embryo develops without the fusion of male and female gametes. While it results in a seed, a typical outcome of sexual reproduction, the process itself is asexual, creating offspring that are genetically identical clones of the parent plant.
2. What are some common examples of plants that exhibit apomixis?
Apomixis is naturally found in several plant families. Some of the most common examples studied under the CBSE syllabus include:
- Certain species of Grasses (Poaceae family)
- Plants from the Asteraceae family (e.g., Dandelions)
- Citrus fruits (like oranges and lemons)
- Certain varieties of Mango
3. What is the fundamental difference between recurrent and non-recurrent apomixis?
The key difference lies in the ploidy (chromosome number) of the embryo sac and the resulting plant.
- Recurrent Apomixis: The embryo sac is developed from a diploid (2n) cell, meaning it does not undergo meiotic reduction. The resulting embryo is also diploid, and the plant is fertile.
- Non-recurrent Apomixis: The embryo sac develops from a haploid (n) cell, typically after meiosis. The resulting embryo is haploid, leading to sterile plants.
4. How does apomixis differ from parthenocarpy?
These are two distinct processes often confused. The primary difference is the final product:
- Apomixis results in the formation of a viable seed (with an embryo) without fertilisation.
- Parthenocarpy results in the development of a fruit without fertilisation, which is why these fruits (like bananas) are typically seedless.
5. What is the connection between apomixis and the phenomenon of polyembryony?
Apomixis can directly lead to polyembryony, which is the occurrence of more than one embryo in a single seed. In some apomictic plants like Citrus, embryos can develop not only from the egg cell but also from other diploid cells in the ovule, such as the nucellus or integuments. These additional apomictic embryos grow alongside the zygotic embryo (if one forms), resulting in multiple embryos within one seed.
6. Why is apomixis considered a highly desirable trait in agriculture and the hybrid seed industry?
Apomixis offers significant advantages for crop improvement:
- Preservation of Hybrid Vigour: Hybrids often have superior traits (heterosis), but these traits segregate and are lost in the next generation. Apomixis creates clonal seeds, preserving the desirable hybrid characteristics indefinitely.
- Cost-Effective for Farmers: If hybrid crops were apomictic, farmers could save seeds from their harvest to plant the next year, eliminating the need to buy expensive new F1 hybrid seeds each season.
- Rapid Multiplication: It allows for the rapid cloning of genetically uniform plants with desirable traits.
7. If apomixis is so beneficial, what are its main limitations or disadvantages in nature?
Despite its agricultural benefits, apomixis has major evolutionary drawbacks. The primary limitation is the lack of genetic diversity. Since offspring are clones of the parent, there is no genetic recombination. This uniformity makes the entire plant population highly vulnerable to new diseases, pests, or sudden environmental changes, as they lack the genetic variation needed to adapt.
8. How can a botanist or researcher determine if a plant is reproducing via apomixis?
Identifying apomixis requires careful scientific investigation. The primary method is through cytoembryological studies, which involve microscopically examining the plant's ovules. Researchers look for evidence that key sexual processes are being bypassed, such as the development of an embryo sac from a somatic cell instead of a megaspore or the formation of an embryo without any sign of pollen tube entry or fertilisation. Genetic analysis can also be used to confirm that the offspring are genetically identical to the maternal parent.
