With the advent of large-scale genetics and an

 

With
the advent of large-scale genetics and an increased consciousness of
polyploidization in plant diversification and evolution, attention in genome
size variation in eukaryotes has increased considerably over the past period (Oliver et al. 2007). Furthermore,
predominantly in plants, a great deal of research has been concentrated for
gene repetition and whole genome duplication events (De Storme and Mason 2014). Nonetheless,
information regarding the mechanisms involved in genome augmentation, and to
extent implementation for breeding, is scarce.

Polyploids
have a prominent breeding significance as they can lead to greater vegetative
harvests, higher quality, superior tolerance against biotic and abiotic
stresses and greater geographic dispersion (Dewitte et al. 2012; Younis et al. 2014). The two
central modes of polyploidization are asexual polyploidization via somatic cell
chromosome doubling and sexual polyploidization through the formation of
functional 2n gametes. In this respect, 2n
gametes are invaluable to the development of polyploids. As a consequence, 2n gamete exploitation is a significant method
to polyploidy as they produce ‘in one step’ novel (autopolyploids or
allopolyploids) species (Brownfield and Köhler 2011; Younis et al. 2014). Furthermore,
sexually (meiotic) formed polyploids, versus somatic (mitotic) polyploids, can
be of immense significance in breeding programs for they can associate genetic attribute
of polyploidy with sexual hybridization and meiotic crossovers (Dewitte et al. 2012; Younis et al. 2014). As a
consequence 2n gametes are invaluable
in terms of enrichment of genetic variability and heterosis.

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The
formation of 2n gametes is usually due to genetic or environmental influences that
lead to meiotic declinations during micro- and megasporogenesis (Brownfield and Köhler 2011). Consequently,
polyploids are formed after the union of two gametes (2n + 2n, bilateral
pathway), or the uneven ploidy level combination (2n + n, unilateral pathway), and
backcrossing to a diploid to form higher ploidy levels (den Nijs and Peloquin 1977; Husband 2004). Sources of 2n gametes ought to be properly
identified when utilized in breeding programs. Most of the detection procedures
concentrate on pollen, since it is far-off less elaborate to screen than egg
cells (Dewitte et al. 2012). Therefore,
detection of 2n pollen can be accomplished using four distinctive procedures: (i)
pollen grain size assessment, (ii) direct estimation of DNA content in gametes
via flow cytometry, (iii) cytogenetic investigation of the microsporogenesis,
and (iv) ploidy-level analysis of the offspring (Bretagnolle and Thompson 1995). Unfortunately,
even though there are ample reports of 2n
gametes in individual plants (ornamental, cultivars and hybrids), still assessments
of the occurrence and diversity of 2n
gametes in natural populations are limited (Kreiner et al. 2017).

Avena ventricosa Bal.
ex Coss. is an endemic C-genome diploid species (Cyprus is the only recorded region
in Europe) having plausible role in the evolution of Avena spp. polyploids via interspecific hybridization (Nikoloudakis and Katsiotis 2008; Liu et al. 2017). Nevertheless,
its populations remain largely uncharacterized, eventhough it encompass a vast
breeding potential due to the large genetic affinity to the cultivated
hexaploid oats (Katsiotis et al. 1995) and due to
its biotic stress tolerance (Loskutov 2001).

The
main objective of the current study was to identify genotypes of A. ventricosa populations, which have
the capacity of producing 2n gametes
as a first step for utilization in breeding schemes. For that reason, we screened
individuals for pollen grain size variability and flow cytometric analysis to
detect 2n gametes. After identifying
2n gamete producers, Pollen Mother
Cells (PMCs) were analyzed to possibly detect the underlined mechanism(s)
resulting in their development.

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