Apomixis occurs in more than 35 plant families, including grains such as corn and wheat. The word ‘apomixis’ has a Greek origin – ‘APO’ means “away from” and ‘MIXIS’ means “act of mixing or blending”. Antonie van Leeuwenhoek discovered the phenomenon of apomixis in orange seed in 1719.
Special mode- apomixis involves the formation of seeds without fertilization. Genetic reunification is not found in apomixis as there is no mixing between male and female gametes. This procedure appears to be effective in maintaining a hybrid seed as there is no meiosis involved. Apomixis is a relatively inexpensive and time-efficient seed production process that assists farmers to plant hybrid seeds. In addition, it may seem commercially viable as high-end features can be passed on to new generations.
Apomixis in plants refers to the reproductive process that occurs in a seed, in which embryos develop without fertilization. That means the reproductive organs of related structures are involved, but no zygote is formed by gametic integration. Therefore, Apomixis is a special breed of asexual reproduction that replaces normal reproduction. The resulting embryo, including a baby plant, resembles its mother’s genetic code. In addition, these plants are virtually free of harmful bacteria.
Certain types of plants may produce embryos without fertilization of eggs and pollen. This condition is called apomixis in plants, and the seedlings produced by this process are known as ‘apomicts’. The term, ‘apomixis’ was coined by botanist Hans Winkler in 1908, as a special form of asexual reproduction ‘without fertilization’. It should be noted that the normal production of asexual plants, such as dispersal from leaves, cannot be considered apomixis. However, replacing plants or replacing bulbil with flowers is considered apomixis.
Depending on the cell involved, the occurrence, and the frequency, Apomixis is divided into four groups.
In this apomixis, the embryonic stem grows without meiosis from diploid cells. The deployed cell has paired chromosomes. Both egg and fetus are diploid. Thus, this new egg has a normal number of chromosomes the size of a mother plant. The embryo evacuates from the egg nucleus without fertilization. Examples of plant species are ‘Crrepis’ and ‘Allium’.
In the recurrent apomixis, the embryo develops directly into the egg cell of the haploid sac or other haploid cells without fertilization. The haploid cell has a single set of organic chromosomes. Therefore, the embryonic embryo is also haploid and infertile. This type of apomixis is uncommon in plant species and is highly dependent on genetic interest. Examples of plant species are ‘Solanum nigrum’ and ‘Lilium’.
Also known as sporophytic budding or nucellar embryonic. It is a type of sporophytic apomixis. The embryo grows directly from a nucellus or a group of nucellus cells or integuments, leading to the formation of a shoot-like structure. The resulting embryonic stem cells are diploid just as the nucleus cells are diploid. Nucellar embryonic usually occurs in tropical and subtropical climates, including citrus and mango.
In this type of apomixis, vegetative buds are called bulbils that grow instead of flowers. These bulbs are easy to produce and may grow into new plants while attached to the mother plants. This type of apomixis is most common in ‘Allum’, ‘Poa’, ‘Bulbosa,’ and other grasses.
Apomixis occurs most commonly in sweet oranges, grapes, lemons, dandelions, hawthorn, blackberries, meadow grasses, and hawkweed.
Apomictic plants inherit the genes of their mother plants, enabling them to maintain genetic similarity for many generations. The main advantages of apomixis are as follows:
The main disadvantages of special-apomixis methods are as follows:
Special methods of apomixis have been shown to be beneficial in the plant breeding industry. This method helps to improve the seed without adding fertilizer. Since there is no meiosis during seed formation, high seed characteristics remain the same. These positive traits are passed on to the next generation, thus maintaining the hygiene of the hybrid seed.
Hybrid seeds are expensive to plant. However, special modes-apomixis help farmers to grow crops all year round without having to buy hybrid seeds. Therefore, the apomixis process proves to be costly for farmers. Apomixis is also a time-saving process. Hybrid seeds allow farmers to plant crops every year because they give a higher yield in a shorter time.
In all production methods, specialized methods – apomixis and polyembryony are very common in both plants and animals. In animals, apomixis occurs when a young person grows into an unfertilized egg.
Among the asexual methods of reproduction, the special methods-apomixis and parthenocarpy are remarkably similar. In either case, fertilization is not involved. In addition, they both use the genitals of plants.
Sexual reproduction is suppressed or absent from a variety of apomictic plants. Facultative apomixis means that apomixis does not always happen and that sexual intercourse also occurs. On the other hand, when sexual reproduction is completely suppressed or absent, it is called apomixis bound to plants.