A preliminary molecular phylogeny of Pennisetum and Cenchrus (Poaceae‐Paniceae) based on the trnL‐F, rpl16 chloroplast markers

Abstract

Pennisetum (80–140 species) and Cenchrus (16–22 species) are closely related genera of Paniceae, both distributed in tropical and sub‐tropical regions. The distinction between Pennisetum and Cenchrus is not clearly defined, and currently no comprehensive taxonomic treatment is available for either genus. Chloroplast DNA sequence data (rpl16, trnL‐F region) were analyzed to test their monophyly, species relationships, and infrageneric classifications. Phylogenetic analyses of individual genomic regions, and a combined dataset, including indel‐coded information, were performed under parsimony and Bayesian inference. Selected geographical, chromosomal and morphological characters were mapped onto the phylogeny to investigate evolutionary trends. Our results support a monophyletic bristle clade and the close relationship between Pennisetum and Cenchrus. Excluding Pennisetum lanatum, Pennisetum is paraphyletic because Cenchrus is nested within it. Sections Pennisetum and Gymnotrix are polyphyletic. Our molecular phylogenetic results show a close relationship among the domesticated species P. glaucum, P. purpureum, P. squamulatum, P. nervosum, and P. sieberianum, suggesting the potential use of these species in crop improvement. The Pennisetum‐Cenchrus clade shows an independent reduction (x = 5, 7, 8) or duplication (x = 17) of the basic chromosome number from the ancestral x = 9. American Pennisetum and Cenchrus species appear to have originated from Old World species more than once. A core group of American species of Cenchrus with a basic chromosome number of x = 17 and retrorsely barbed bristles could be restricted to Cenchrus s. str.

Evolution of the apomixis transmitting chromosome in Pennisetum

“…Polyphyly in Cenchrus was supported by additional chloroplast sequence data and taxon sampling [27]. Our data support the placement of Cenchrus within Pennisetum , but are incongruent with the result of Donadio [27] and Chemisquy [26] that showed a close relationship between one accession of P. purpureum , P. setaceum , and Cenchrus spp .…”

“…Polyphyly in Cenchrus was supported by additional chloroplast sequence data and taxon sampling [27]. Our data support the placement of Cenchrus within Pennisetum , but are incongruent with the result of Donadio [27] and Chemisquy [26] that showed a close relationship between one accession of P. purpureum , P. setaceum , and Cenchrus spp . In the ITS-based phylogeny of Martel [24], P. setaceum and P. villosum grouped with species from section Brevivalvula in a clade that included Cenchrus ciliaris ; therefore, their placement of P. setaceum , but not P. villosum , was more consistent with Donadio [27].…”

“…Earlier attempts to resolve phylogenetic relationships among different species in the genus Pennisetum or higher taxonomic levels including Pennisetum were based on multiple approaches such as genome size variation [39], molecular markers [40,41], and DNA sequence information from a) the internal transcribed spacer region of ribosomal DNA [24], b) the nuclear gene knotted [42,26], and c) the chloroplast genes ndh F [25,26,42-44], rpo C2 [45], and rpl16 / trn L-F [26,27]. The present study, focused on apomixis, included twelve apomicts and eight sexual species.…”

“…Br., and at least 17 aposporous species [18]. Relationships have been inferred among some of these species using basic chromosome numbers, ITS (the internal transcribed spacers of ribosomal RNA genes) DNA data [24] and sequences from chloroplast genes such as ndh F (F subunit of NADH dehydrogenase) [25], ndh F and trn L-F [26], trn L-F and rpl 16 [27]. Chemisquy [26] also used a nuclear gene ( knotted ) to study the phylogeny in Cenchrus , Pennisetum and related genera.…”

Phylogenetic relationships of Echinolaena and Ichnanthus within Panicoideae (Poaceae) reveal two new genera of tropical grasses

“…However, it is worth pointing out that the ndhF gene and the rpl16 region (almost entirely composed of the rpl16 intron) were the most variable among plastid data sets. The ndhF gene has been widely used in phylogenetic studies within Panicoideae (e.g., Giussani et al, 2001;Aliscioni et al, 2003;Sánchez-Ken and Clark 2010;Morrone et al, 2012), as well as the rpl16 region (e.g., Donadío et al, 2009;Giussani et al, 2009;Salariato et al, 2010;Scataglini et al, 2014a), proving to be very useful for phylogenetic reconstruction within the subfamily. The transition/transversion ratio (ts : tv) was high for coding regions and low for noncoding regions as expected (Table 3), because transitions are less likely to result in amino acid substitutions.…”