An apomictic tetraploid Paspalum chaseanum cytotype and its cytogenetic relationship with P. plicatulum (Poaceae): taxonomic and genetic implications

Abstract

Paspalum chaseanum Parodi (Poaceae) is a rare species seldom found in the vast phytogeographic Chaco region of South America. It occurs in some localities as a diploid with 20 somatic chromosomes, reproduces sexually and is self-incompatible. A tetraploid cytotype was recently collected in this geographic region. This accession was determined to reproduce of aposporous apomixis and was crossed, as pollen donor, onto a sexual autotetraploid plant of P. plicatulum Michx. The meiotic chromosome pairing behaviour of both parents and their hybrids was primarily as bivalents and quadrivalents, indicating that tetraploid P. chaseanum is likely to have an autoploid origin, and that both species share basically the same genome. Although some controversies exist regarding the subgeneric taxonomic classification of P. chaseanum, these results support its inclusion in the informal Plicatula group of Paspalum. The P. plicatulum × P. chaseanum hybrids segregated for apomixis. The amount of seed set in some hybrids (up to 17%) and the presence of sexual as well as facultative apomictic individuals in the progeny suggest that gene transfer through hybridisation is a feasible tool in genetic-improvement programs concerning these forage grass species.

Interspecific hybrids between Paspalum plicatulum and P. oteroi: a key tool for forage breeding

“…This might affect the transmission and expression of some genes in the F 1 interspecific progeny. A similar situation occurred with the inheritance of the pubescent-spikelet trait of P. chaseanum Parodi that was transmitted to the entire progeny when the species was hybridized with accession 4PT of P. plicatulum (Novo et al, 2013), while none of the hybrids has pubescent spikelets when we crossed the same P. plicatulum genotype with P. oteroi, a species also characterized by pubescent spikelets. Cytologically, P. plicatulum and P. chaseanum are autotetraploid, share homologous genomes and their interspecific hybrids show patterns of cytogenetic behavior very similar to autotetraploids while the P. plicatulum × P. oteroi hybrids showed meiotic chromosome configurations of allotetraploids or segmental allotetraploids.…”

“…There is a large list of previous reports indicating that segregation for reproductive mode occurs among individuals of an F 1 progeny when a sexual plant is crossed with an apomictic one in several species of Paspalum (e.g., Martínez et al, 2001;Stein et al, 2004;Aguilera et al, 2011;Novo et al, 2013). Consequently, segregation for the reproductive mode was also expected among the P. plicatulum × P. oteroi hybrids.…”

“…Mature ovaries collected at anthesis were clarified and observed with a differential interference contrast microcopy (DIC) following the same procedures that were used before (Novo et al, 2013). Because, in Paspalum, the sexual and the aposporous embryo sacs differ in their internal structure and structure, this technique allows assessing the reproductive mode by observing the type of embryo sac in mature ovules.…”

“…This obstacle may be overcome by doubling the number of chromosomes of diploid plants to produce sexual tetraploids (Forbes and Burton, 1961;Sartor et al, 2009). Sexual induced-tetraploid germplasm of P. plicatulum is currently available (Sartor et al, 2009) and easily hybridizes with other species of the Plicatula group as pollen donors (Aguilera et al, 2011;Novo et al, 2013). This study aimed to hybridize sexual tetraploid P. plicatulum with apomictic tetraploid P. oteroi to establish their cytogenetic relationship and to determine the reproductive behavior and fertility of the hybrids in order to explore the possibility of gene exchange in breeding programs of these species.…”

Reproductive Systems in Paspalum: Relevance for Germplasm Collection and Conservation, Breeding Techniques, and Adoption of Released Cultivars

“…The use of hybridization between related species is a suitable approach for breeding in the genus Paspalum . Inter-specific hybrids were generated in the Plicatula group of Paspalum using a chromosome-doubled sexual plant of P. plicatulum and apomictic ecotypes of different species of the Plicatula group (Novo et al, 2013; Pereira et al, 2015; Novo et al, 2016; Novo et al, 2017). New highly apomictic hybrids were generated, and several were characterized as superior for forage yield, cold tolerance, and cattle preference with respect to the apomictic male parent (Da Costa Huber et al, 2016; Motta et al, 2017; Novo et al, 2017).…”