Flowering plants primarily produce seeds through sexual reproduction , which drives genetic diversity . The meiosis for the formation of gametes male and female, and the fusion of gametes fertilization in the egg flower to form embryonic compartment of the seed, leads to the segregation of alleles of seedlings. Surprisingly, some flowering plants asexually form seeds by apomixis . Apomixis comprises a set of developmental processes that together alter the functions reproductive reproductions in the ovule, generating asexual reproduction . As a result, the embryo develops solely from cells in the maternal ovum tissues , and therefore the offspring of the plants are genetically identical to the mother .
What is apomixis?
Apomixis is a form of asexual reproduction for the formation of seeds that produces a clonal progeny or clones with a genotype identical to the maternal genotype . It mainly influences the reproductive events in the flower ovule .
- What is apomixis?
- Types of apomixis
- How Farmers Use the Apomixis Process
- Apomixis in citrus
What is apomixis?
It is a reproductive mechanism that bypasses the sexual process and allows a plant to clone itself through the seed . Apomixis comprises three components of development that deviate from the normal sexual pattern: avoidance of meiosis during cell development when it is in the egg stage , embryo formation independent of fertilization, and generation of viable endosperm with or without fertilization. In other words, it is asexual reproduction through seeds , and it is increasingly seen as a dysregulation of sexual reproduction.
The first time the subject of apomixis was discussed, it was in the year 1841 and it was used to refer to the Australian species Alchornea ilicifolia , a female specimen that was introduced to the Kew Botanical Gardens in London . This plant was isolated and flourished, producing a large number of seeds even without having any source to pollinate itself , showing that it had managed to produce seeds asexually .
The first experiments that were used inadvertently were carried out by Gregor Mendel who, when using crosses between species of the genus Hieracium to confirm his findings in the inheritance of garden peas, gave it the wrong name of self – pollination .
Types of apomixis
There are three different types or mechanisms of apomixis, which are:
- Diplosporia : occurs when the stem cell of the female embryo sac develops directly into an embryo . This process is also known as diploid parthenogenesis and the embryo that is produced through it is diploid .
- Aposporia : it happens when the embryo sac originates from one of the many somatic cells that surround the stem cell of the embryo sac. In this case the embryo is also diploid . Although a gametophyte develops , meiosis does not occur in this case and it does not have any observable consequences.
- Adventitious embryo : in this type of apomixis there is no development of the embryo sac . The embryo then develops from cells of the diploid sporophyte .
The main advantage of apomixis is the use that can be made of the technique as a technology to achieve plant improvement , increasing yield and food safety . In addition, it is possible to establish a specific genotype , which is capable of adapting perfectly to a specific environment.
The main disadvantage of apomixis is that by not presenting any type of genetic exchange , there is the possibility of a disturbance in the environment that could be, for example, a sudden change in temperature, salinity, water availability, and others, and the population that has reproduced by apomixis may become extinct because they do not have any interspecific variability .
How Farmers Use the Apomixis Process
Apomixis, or asexual reproduction through seeds, is a natural trait that could have a huge positive impact on crop production . Apomictic breeding strategies could allow indefinite fixation and propagation of any desired genotype.
Apomixis in citrus
Citrus rootstock propagation depends on the production of clonal nucellar seedlings . This makes apomixis one of the important host traits in programs used to achieve citrus rootstock breeding .
The importance of apomixis is that it manages to prevent the loss of specific characters in the hybrid. In addition, it is a very profitable method to produce seeds and at the same time produce new species in less time. It is possible, through this technique, to create hybrid varieties that have a better yield and a better quality . It is a mechanism that works perfectly to produce disease- free plants and achieve better crop yields.
The most common example that we can mention regarding apomixis is Taraxacum officinalis , a plant that we normally know by the name of Dandelion . We can also find some varieties of onion within this type of reproduction . Other examples can be seen in the genera Crataegus (“hawthorn”), Sorbus (” rowan “), Rubus (“bramble” or “blackberry”), Hieracium .
By grafting many plants it is also reproduced mainly type woody , fruity and citrus fruits such as oranges, tangerines, limes. The avocado or avocado, apples, pears, plums, are also examples of apomixis. As for the flowers we can mention the roses .