Sequential Reduction of Pennisetum squamulatum Genome Complement in P. glaucum (2n=28)*P. squamulatum (2n=56) Hybrids and their Progenies Revealed its Octoploid Status

Abstract

Summary P. squamulatum Fresen. is an important Pennisetum species by virtue of its characters, such as, apomixis, perenniality and stress tolerance, which can be utilized for pearl millet improvement. This species is hitherto believed to be 2nϭ6xϭ54, however, recent reports of 2nϭ56 cytotypes rendered to recheck the ploidy status. In present study, meiotic system of F 1 and advanced hybrids, such as F 2 , F 1 sibs, and BC 1 , involving P. squamulatum (2nϭ56) and P. glaucum (2x and 4x) were investigated following a scheme to sequentially reduce P. squamulatum chromosome complement to half, in order to determine its ploidy. The cytological results indicating high bivalent frequencies in these generations confirmed octoploid (instead of 6x) nature of P. squamulatum, alongwith its basic chromosome number as 7 (similar to pearl millet) with its allo-octoploid (or auto-allo octoploid) status. On the basis of cytogenetical studies viz. crossability, DNA content, genetic relatedness and cytology of advanced hybrids, placement of P. squamulatum in secondary gene pool of pearl millet is supported.

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

“…The variation between GOS hybrids for several characters (Table 2) might be because of the male gametes (GSH1/GSH2), as origin of female gametes was apomeiotic (aposporous). That GSH1 and GSH2 produce genetically variable and reduced pollen has previously been demonstrated in a segregating back-cross population from P. squamulatum using tetraploid pearl millet as recurrent parent (Kaushal et al 2008a).…”

“…Further, a rare hybrid with 2n = 28 (14G ? 14S, GGSS) exhibited all bivalents (14IIs) (Kaushal et al 2008a). Thus, it provides sufficient evidence that the two wild genomes differ significantly from the P. glaucum cultivated genome.…”

“…Peak 1 represented BC1GO while peaks from GSH1/ GSH2 and GOS overlapped because of similar DNA contents (peak 2). Smaller peaks in some histograms arose from cells at G2 phase Kaushal et al 2008a). However, we noticed additive effects of doses from annual parent in determining 'perenniality vigour'.…”

“…9O chromosomes (genomic status GGGSSO). The chromosomes representing different species can be well identified in the hybrid background owing to differences in their sizes and stainability (Zadoo and Singh 1986;Dujardin and Hanna 1983b;Kaushal et al 2008a). The cytological analysis of GOS hybrids at meiosis exhibited highly irregular features.…”

“…P. squamulatum is another perennial grass with tolerance to biotic and abiotic stresses and is obligate apomictic. The species was hitherto believed to be 2n = 9x = 54 (Patil et al 1961), however, recent discovery of 2n = 56 cytotypes (Roy et al 2003;Goel et al 2003), their hybrids with pearl millet (Kaushal et al 2008a) and molecular cytogenetics studies (Akiyama et al 2006) has suggested the species with 2n = 8x = 56 genomic status and a placement in secondary rather than tertiary genepool.…”