Apomixis: new horizons in plant breeding

Abstract

IntroductionApomixis is a mechanism of seed formation without fertilization and is observed in more than 300 species in 30 out of 460 angiosperm families, but it is not common in crop species (Bashaw, 1980). It was considered as an obstacle for plant breeding. Indeed, the presence of apomixis in the species Hieracium, in which Mendel was asked to prove the genetic principles he had developed in peas, caused him to withdraw from the scientific world due to his failure to do so (Carneiro et al., 2006). In recent years, however, apomixis is seen as a way to maintain superior genotypes as clones of seeds. As such, apomixis has been a major area of investigation in plant genetics.Unlike in animals where it is a hot topic nowadays, cloning is an ordinary process in plants. Many plant species can be propagated using various plant parts. Clonal propagation has some advantages as well as disadvantages. Apomixis combines the advantages of propagation by seed (higher multiplication rate, easier storage and planting, suitability for machine planting, less seed material use, and less bearing of diseases) with those of propagation by clone (maintaining genetic structure and hence fixing superior genotypes after crossing). However, apomixis manifests itself in different mechanisms that have not yet been fully elucidated. Genetic studies reveal that, though complicated, the trait is controlled by a few genes (Barcaccia and Albertini, 2013). In addition, different phases of apomictic reproduction have been achieved artificially (d'Erfurth et al., 2009). Apomictic reproduction of crop species would lead to revolutionary developments in terms of crop improvement. The benefits of apomixis are estimated to surpass those of the green revolution (Grossniklaus et al., 1998).The aim of this review paper is to discuss the use of apomixis in plant breeding. Our main attention is on its benefits in crop improvement rather than its physiological nature or molecular mechanisms. Methods to achieve apomixis in crop species and its economic advantages are also discussed. Mechanisms of apomixisThere are various mechanisms of apomixis, some of which result in unstable chromosome numbers (Naumova, 1993). Here we only discuss the ones with stable chromosome numbers and those that are important for plant breeding purposes without going into much detail.Development of apomictic seed formation takes place in three stages: a) suppression of meiosis (apomeiosis), b) endosperm formation without fertilization (parthenogenesis), and c) seed formation with (pseudo-Abstract: Apomixis is seed formation without fertilization, commonly observed in wild plant species. It has the advantages of clonal reproduction and propagation by seeds. Although it has a complex inheritance, genes controlling apomictic reproduction are being identified. Transfer of apomixis to crop species through wide crosses has not been successful so far, but transgenic technology offers a more powerful way to introgress apomixis into crop species. When crop species acquire this trait, superi...

Status of Global Pearl Millet Breeding Programs and the Way Forward

“…Apomixis is a form of asexual reproduction where maternal clones are produced through seeds (Nogler, 1984). Apomixis is commonly observed in wild plant species and can be transferred to cultivated species through crossing with apomictic wild relatives, mutation, or genetic transformation (Kandemir and Saygili, 2015). Apomixis occurs in three major forms: adventitious embryony (seeds develop directly from somatic cells, usually nucellar), diplospory (development of a 2 n embryo sac from the megaspore mother cell), and apospory (one or more nucellar cells develop into 2 n embryo sacs with either seven cells [Hieracium type] or four cells [Panicum type]) (Morgan et al, 1998).…”

“…Successful transfer of apomixis into crop species, which naturally reproduce through sexual means, holds great promise for improving seed production (Vielle et al, 1996). The development of apomictic seed has three stages: (i) suppression of meiosis (apomeiosis), (ii) endosperm formation without fertilization (parthenogenesis), and (iii) seed formation with fertilization (pseudo‐apomixis) or without fertilization (autonomous apomixis) (Kandemir and Saygili, 2015). In pseudo‐apomixis, the young embryo is aborted before mature embryo sac formation and replaced by developing aposporous sacs (Barcaccia and Albertini, 2013).…”

Synthetic Apomixis an Old Enigma to Preserve Hybrid Vigor

“…Sexual hybridization to transfer apomixis through interspecific hybridization rely heavily on the availability of wild relatives. In maize the apomixis was transferred from its wild relative Tripsacum through hybridization whereas, the produced hybrid after series of backcrosses was sterile in nature and facultative apomicts were not produced to recover maize genome [46]. So far, it is generally believed the transfer of apomixis through wide crosses is not a successful approach.…”

Yield Evaluation of Selected Clones Apomictic Iles-Iles (Amorphophallus muelleri Blume) on Second Growing Period

“…Developing new variety in A. muelleri is rarely studied because it produces apomictic seed (agamosporous) that set without fertilization (Dani, 2008). It is known that apomict causes low genetic variation in many plants (Barcaccia and Albertini, 2013;Kandemir and Saygili, 2015). Nevertheless genetic variation in the A. muelleri has been noted (Poerba dan Martanti, 2008;Sedayu et al, 2010;Mekkerdchoo et al, 2011;Rosidiani et al, 2013;Nikmah et al, 2016;Santosa et al, 2018).…”