Nuclear DNA content and chromosome number in Brachiaria spp. genotypes

Abstract

Breeding programs for Brachiaria spp. use both intraspecies and interspecies crosses between sexual and apomictic plants in order to obtain new cultivars with the desired characteristics. As there are different ploidy levels both within and between species of this genus, it becomes necessary to evaluate the genotypes used in breeding programs, as a guide to breeders when adopting crossing strategies. In this work, DNA content and chromosome number were determined in order to characterise ploidy levels in Brachiaria spp. genotypes. In the analysis of 15 genotypes, DNA content varied with the ploidy levels (2x, 3x and 4x), and between species and/or taxon. The average DNA content was 1.74 pg (2x) in B. ruziziensis, 3.74 pg (4x) in B. decumbens and 3.52 pg (4x) for B. brizantha. For the genotype 86, 2.57 pg of DNA was obtained and 2n = 3x = 27, indicating a triploid accession, probably a natural hybrid. The variation in the total DNA content allowed the differentiation of Brachiaria ruziziensis (2n = 2x = 18) from the tetraploid species Brachiaria Brizantha and Brachiaria decumbens (2n = 4x = 36), as well as the probable hybrid triploid (2n = 3x = 18) of these species.