Ploidy manipulation in guinea grass (Panicum maximum Jacq., Poaceae) utilizing a Hybridization‐supplemented Apomixis‐components Partitioning Approach (HAPA)

Abstract

Ploidy manipulations are achieved by utilizing unreduced gametes, somatic chromosome doubling or haploidization. Apomixis, the asexual mode of reproduction through seeds, involves two of these phenomena viz., apomeiosis (unreduced embryo-sac formation) and parthenogenesis (fertilization-independent embryogenesis). The two components when partitioned may yield high frequencies of triploids and haploids, and thus, serve as a tool to manipulate ploidy levels when appropriately supplemented with hybridization schemes. Utilizing this Hybridization-supplemented Apomixis-components Partitioning Approach (HAPA), the largest ploidy series in a crop plant was generated in guinea grass (Panicum maximum Jacq.). Eighty-nine diverse guinea grass accessions were characterized for their reproductive capacities to identify tetraploid (2n = 4x = 32) accession(s) with high apospory but reduced parthenogenetic capacity, thereby producing a high frequency of hexaploid seeds. Seeds from accession IG 04-164 were utilized to produce a ploidy series by appropriately combining partitioned apomixis components and hybridizations in two seasonal cycles. We successfully obtained plants representing ploidies 3x, 4x, 5x, 6x, 8x and 9x, all derived from a single 4x progenitor. Production methodology, reproducibility and utilization of HAPA in cytogenetic and molecular studies are discussed.

Development and Characterization of a Hexaploid <i>Pennisetum orientale</i> (2<i>n</i>=6<i>x</i>=54) Cytotype Recovered through B_III Hybridization

“…Uncoupling apomeiosis from parthenogenesis would require fertilization of an unreduced egg cell to develop an embryo and thus yielding 3n progeny through 2n+n hybridization and are termed as B III hybrids (Ozias-Akins and van Dijk 2007, Kaushal et al 2008). Such hybrids with 3n genomic constitution have already been reported in crops such as Poa pratensis (Albertini et al 2001), Panicum maximum (Kaushal et al 2009), Cenchrus ciliaris (Conner et al 2013) and Pennisetum spp. (Bashaw et al 1992), whereby they offer advantages for gene transfer in otherwise apomictic crops and means to manipulate ploidy Hignight 1990, Kaushal et al 2009).…”

“…apomeiosis, parthenogenesis and functional endosperm development, are linked functionally and maintain clonal reproduction in apomictic seed development. However, uncoupling of these components has been demonstrated recently in several crops, thereby generating modified ploidies and diversity in pathways of seed development (Matzk et al 2005, Kaushal et al 2008, 2009). Uncoupling apomeiosis from parthenogenesis would require fertilization of an unreduced egg cell to develop an embryo and thus yielding 3n progeny through 2n+n hybridization and are termed as B III hybrids (Ozias-Akins and van Dijk 2007, Kaushal et al 2008).…”

“…Cytological analysis on meiosis (diakinesis stage) and pollen fertility was done by staining pollen mother cells and pollen grains, respectively, at appropriate stages of development, in 2% acetocarmine. Estimation of DNA quantity was done by measuring relative DNA content using flow cytometry from leaf tissues (Kaushal et al 2009). …”

“…However, owing to recent knowledge on uncoupled apomixis components, fertilization of unreduced egg cell with reduced pollen (known as 2n+n or B III hybridization) (Rutihauser 1948) is one of the possible approaches to obtain gene transfer. Uncoupling of the apomixis components (apomeiosis, parthenogenesis and functional endosperm development) has been recently reported in several agamic species (Kaushal et al 2009). Objectives of this study were to provide evidence of B III hybridization in P. orientale and characterization of 6x cytotype (2n=54) recovered through such uncoupling events in 4x cytotype (2n=36).…”

Morphological, cytological and reproductive characterization of tri-species hybrids (GOS) between Pennisetum glaucum, P. orientale and P. squamulatum

“…However, uncoupling of these components has now been demonstrated in several taxa, such as Poa pratensis (Albertini et al 2001), Erigeron (Noyes 2006), Taraxacum (van Dijk et al 2003Zavesky et al 2007), Hieraceum (Okada et al 2007), Boechera holboellii (Kantama et al 2007) and Panicum maximum (Kaushal et al 2008b). Partitioning of apomeiosis and parthenogenesis enhances the frequency of M I and/or B III hybrids (Matzk et al 2005;Zavesky et al 2007;Kaushal et al 2009), and may also lead to autonomous endosperm development in crops otherwise characterized by pseudogamous development (van Dijk et al 2003;Noyes 2005;Kaushal et al 2008b).…”