An investigation of chromosome numbers in the genus Brachiaria (Poaceae: Paniceae) in relation to morphology and taxonomy

Abstract

Determinations of chromosome number and morphological studies of 260 populations, belonging to 32 taxa, of the genus Brachiaria from the Indian subcontinent reveal that all sexually reproducing taxa have no chromosome races. Six agamic taxa, viz., B. brizantha var. brizantha (n = 27), B. brizantha var. ciliata (n = 18), B. decumbens (n = 18), B. hybrida (n = 27), B. mutica (n = 18), and B. setigera var. albistyla (n = 14), have consistently shown uniformity in chromosome numbers, based on x = 7, 8, and 9. Brachiaria setigera var. setigera, a genetically unstable apomict, is the only taxon that tends to have a heteroploid series (n = 16, 17, 18, 21, and 32). The population of B. setigera var. setigera with n = 17 is based on a secondary base number of x = 17. There are 6 diploids, 20 tetraploids, 5 hexaploids, and 3 octoploids in the genus. Aneuploidy and triploidy are characteristically absent in the genus, although their plausible existence in the B. setigera complex cannot be ruled out. In several species certain previously reported chromosome numbers that deviate from the present study are found to be the result of erroneous identifications or the result of taxonomically complex situations such as those found in B. brizantha, the B. distachya complex, and the B. ramosa complex.

Microsporogenesis in Brachiaria brizantha (Poaceae) as a selection tool for breeding

“…The same basic chromosome number (x = 9) was recorded for this species by other authors (see Valle and Pagliarini, 2009). Diploidy (2n = 2x = 18) was reported in only a few accessions (Basappa et al, 1987;Mendes-Bonato et al, 2002), but tetraploids always prevail (see Valle and Pagliarini, 2009). In attempt to aid the Brachiaria breeding program underway at Embrapa Beef Cattle and to determine the ploidy level of the accessions of different species to initiate an interspecific hybridization program, DNA content was measured by flow cytometry (Penteado et al, 2000).…”

Meiotic behavior of a nonaploid accession endorses x = 6 for Brachiaria humidicola (Poaceae)

“…The data on the meiotic behavior of H003 and H030 ascertained that they are heptaploids derived from x = 6. Two basic chromosome numbers, x = 7 and x = 9, have been reported for the genus Brachiaria, with a large prevalence of x = 9 (Basappa et al, 1987;Honfi et al, 1990;Valle and Savidan, 1996;Bernini and Marin-Morales, 2001;Utsunomiya et al, 2005;Mendes-Bonato et al, 2002. However, recently, a new basic chromosome number, x = 6, was determined for several accessions in the germplasm collection of B. dictyoneura at Embrapa (Risso-Pascotto et al, 2006c), a species belonging to the same taxonomic group and closely related to B. humidicola, according to Renvoize et al (1996).…”

“…Polyploidy is widespread in the genus Brachiaria (Basappa et al, 1987;Honfi et al, 1990;Valle and Savidan, 1996;Bernini and Marin-Morales, 2001;Utsunomiya et al, 2005;Mendes-Bonato et al, 2002). An analysis of the DNA content of 435 accessions of 13 species of Brachiaria in the Brazilian collection, maintained at Embrapa Beef Cattle (Campo Grande, MS), revealed that only 13.04% are 2n whereas the others are polyploid, with a large predominance of tetraploids (58.13%) (Penteado et al, 2000).…”

Genome elimination during microsporogenesis in two pentaploid accessions of Brachiaria decumbens (Poaceae)

“…Previous studies in the genus Brachiaria revealed that most species and accessions within the species are polyploid (Pritchard 1967;Nassar 1977;Ndikumana 1985;Basappa et al 1987;Valle and Savidan, 1996;Utsunomiya et al, 2005;Mendes-Bonato et al, 2002Pagliarini et al, 2008;Risso-Pascotto et al, 2003. Among the polyploid accessions there is evidence that some of them evolved from autopolyploidy (MendesBonato et al, 2002) and others from allopolyploidy (Mendes et al, 2006;Boldrini et al, 2009aBoldrini et al, ,b, 2010.…”