Chromosome Number, Genomic Variation, and Molecular Markers to Assess Genetic Diversity of Brachiaria Species
2016
Nitthaisong, Pattama | Ishigaki, Genki | Tanaka, Hidenori | Akashi, Ryo
The genus Brachiaria contains approximately 100 identified species, including economically important tropical grasses; however, there is not much accessible information about the genetics or genomes of the genus. In this study, we determined the chromosome number and genome size by cytological analysis and flow cytometry, respectively, and estimated the molecular variability using intersimple sequence repeat (ISSR) markers for 28 accessions representing 11 Brachiaria species. The chromosome number of 10 species agreed with previous reports, and the chromosome number for B. xantholeuca was evaluated (2n = 4x = 36) for the first time. Genome size expressed as C values differed among these species (0.89 to 4.02 pg/2C) and increased with increasing ploidy levels. In contrast, the genome size given as a Cx value tended to decrease with increasing ploidy levels in polyploid plants. A total of 441 ISSR fragments were generated with 10 primers to assess the molecular variability of Brachiaria species. All 11 Brachiaria species clustered into three groups with the neighbor-joining (NJ) method. We found no correlation between the clusters and the region from where the plants were collected. Nevertheless, the clustering of accessions was clearly correlated with ploidy level and reproductive mode (sexual and apomictic) except for a few accessions. Furthermore, evolution of the Brachiaria genome and genetic diversity within the genus were discussed.
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