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:
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It is an asexual means of plant reproduction and is found in many species especially in fruit crops.
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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.
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It helps in the rapid development of pure lines and can be achieved by haploid parthenogenesis.
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Apomixis can be genetically controlled and is useful in conserving superior genotypes and hybrid vigor.
Apomixis Classification
Apomixis can be classified based on:
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Cell involved
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Occurrence
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Frequency
Apomixis Types:
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Classification |
Types of apomixis |
Description |
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Cell involved apomixis |
Parthenogenesis |
The embryo develops from an egg cell |
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Apogamy apomixis |
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Diplospory |
The unreduced embryo sac is derived from a megaspore mother cell by aborted meiotic division or a direct mitotic division. The major types of diplospory apomixis are Taraxacum, Ixeris, and Antennaria. In Taraxacum, the meiotic prophase starts but then the phase is aborted which results in two unreduced dyads one of which gives rise to the embryo sac by mitosis In Ixeris, two further mitotic divisions of the nuclei give rise to an octa-nucleate embryo sac which follows an equational division following meiotic prophase. In Antennaria, a total of three mitotic divisions form the megagametophyte. |
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Apospory |
The nuclear cells that give rise to apomictic embryo sacs which are known as aposporos initials are distinct from the ameiotic megasporocyte. The aposporos initial cells may differentiate close to the ameiotic megasporocyte and transform into an apomictic embryo sac. After they differentiate then enter mitotic cell division to produce an embryo sac. Some ovules can contain several embryo sacs and, depending on the plant species, the form of the embryo sac may be – different from that seen in the sexual reproduction process. The initiation apospory embryo sac can occur alongside a sexual one or it can inhibit sexual embryo sac formation. |
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Adventive embryony |
It is also known as sporophytic apomixis. In this type of apomixis, there may be a megagametophyte in the ovule. However, the embryos do not rise from the cells of the gametophyte. They rise from the cells of the nucleus. It can be observed in species of Garcinia, Mangifera indica, etc |
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Occurrence |
Recurrent apomixis |
It is also called gametophytic apomixis The megagametophyte has the same number of chromosomes as the mother plant. This is due to incomplete meiosis. It generally arises from an archesporial cell or some other part of the nucleus. |
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Non-recurrent apomixis |
The embryo sac consists of haploid cells and the embryo develops from a haploid cell. |
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Frequency |
Obligate apomixis |
The reproduction takes place by apomictic means |
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Facultative apomixis |
The process of reproduction is carried out by both apomictic and sexual means. |
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:
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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.
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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:
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Rapid multiplication of genetically uniform progenies without the risk of segregation.
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Hybrid vigor or heterosis can be fixed permanently in crop plants.
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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.