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
What are the salient features of recurrent and non-recurrent apomixis?
Recurrent apomixis
The embryo-sac is developed from diploid cells without a reduction in chromosome number.
The plants produced by recurrent apomixis have diploid (2n) number of chromosomes.
All recurrent apomixis produced plants are fertile
Non-recurrent apomixis
The embryo-sac has haploid cells (n).
Plants produced by non-recurrent apomixis are haploid and sterile.
The method includes haploid apogamy and haploid parthenogenesis
This method is used in the development of inbred lines.
What are the limitations of apomixis?
The limitation of apomixis are:
Genetic diversity: Other than obligate apomictic lines that show low genetic diversity, apomictic lines are genetically highly uniform. The diversity shows through mutation.
Lack of gene flow: Re-combinations do not occur in such apomictic populations, therefore there is a lack of gene flow.
Selection is ineffective: Selection is ineffective in obligate apomictic lines due to lack of heritable variation. All the plants of an apomictic line have the same genotype. It can either be homozygous or heterozygous.
Low frequency: Apomictic lines have very low frequency and are available in limited crop plants. However, these lines are more frequent in fruit crops.
What are the major uses of Apomixis in plant breeding?
Apomixis is used vastly in plant breeding because:
Rapid multiplication of genetically uniform individual plants can be achieved without the risk of segregation of varieties.
Heterosis or hybrid vigor can permanently be fixed in crop plants, thus no problem for recurring seed production of F1 hybrids.
Efficient exploitation or the destruction process of the available maternal effect, if present, is possible to be passed on from generation to generation.
Homozygous inbred lines, that are identified in every possible corn variety, can be rapidly developed as they produce sectors of diploid tissues and occasional fertile cells or seeds.
How is Apomixis exploited in the process of crop improvement?
The use of apomixis in any variety of plants or crops in a follow-up process, after a variety or hybrid is evolved, is reflected by the benefits it renders after the final process. Apomixis is dealt with only as a tool to plant breeding and developing the parent plant. With a view to exploiting apomixis in sexual crops, it needs to detect and identify an apomictic phenomenon, occurring spontaneously in any plant, or, incorporate it artificially, perhaps through hybridization between apomicts and amphimixis.
How can you detect the presence of Apomixis?
Positive evidence for the presence or absence of apomixis in a plant can be obtained only from an intensive screening of a large variety of different plants or a varied hybrid of plants. The final screening process involves a careful and systematic tracing of necessary steps for the development of embryo-sac and embryo in a plant, through microtomy of the ovule, right from megaspores to embryonic development.
