Ortiz Alejandra Marcela, Robledo Germán, Seijo Guillermo, Valls José Francisco Montenegro, Lavia Graciela Inés
Instituto de Botánica del Nordeste (CONICET-UNNE), CC 209, Sargento Juan Bautista Cabral 2131, 3402BKG, Corrientes, Argentina.
Facultad de Ciencias Exactas y Naturales y Agrimensura (UNNE), Av. Libertad 5000, 3402BKG, Corrientes, Argentina.
J Plant Res. 2017 Sep;130(5):791-807. doi: 10.1007/s10265-017-0949-x. Epub 2017 May 23.
Rhizomatosae is a taxonomic section of the South American genus Arachis, whose diagnostic character is the presence of rhizomes in all its species. This section is of particular evolutionary interest because it has three polyploid (A. pseudovillosa, A. nitida and A. glabrata, 2n = 4x = 40) and only one diploid (A. burkartii, 2n = 2x = 20) species. The phylogenetic relationships of these species as well as the polyploidy nature and the origin of the tetraploids are still controversial. The present study provides an exhaustive analysis of the karyotypes of all rhizomatous species and six closely related diploid species of the sections Erectoides and Procumbentes by cytogenetic mapping of DAPI/CMA heterochromatin bands and 5S and 18-26S rDNA loci. Chromosome banding showed variation in the DAPI heterochromatin distribution pattern, which, together with the number and distribution of rDNA loci, allowed the characterization of all species studied here. The bulk of chromosomal markers suggest that the three rhizomatous tetraploid species constitute a natural group and may have at least one common diploid ancestor. The cytogenetic data of the diploid species analyzed evidenced that the only rhizomatous diploid species-A. burkartii-has a karyotype pattern different from those of the rhizomatous tetraploids, showing that it is not likely the genome donor of the tetraploids and the non-monophyletic nature of the section Rhizomatosae. Thus, the tetraploid species should be excluded from the R genome, which should remain exclusively for A. burkartii. Instead, the karyotype features of these tetraploids are compatible with those of different species of the sections Erectoides and Procumbentes (E genome species), suggesting the hypothesis of multiple origins of these tetraploids. In addition, the polyploid nature and the group of diploid species closer to the tetraploids are discussed.
根状花生组是南美洲花生属的一个分类学组，其诊断特征是所有物种都有根状茎。该组具有特殊的进化意义，因为它有三个多倍体物种（拟绒毛花生、光亮花生和光叶花生，2n = 4x = 40），而只有一个二倍体物种（布尔卡花生，2n = 2x = 20）。这些物种的系统发育关系以及多倍体性质和四倍体的起源仍存在争议。本研究通过DAPI/CMA异染色质带以及5S和18 - 26S rDNA位点的细胞遗传学定位，对所有根状茎物种以及直立花生组和匍匐花生组的六个近缘二倍体物种的核型进行了详尽分析。染色体带型显示DAPI异染色质分布模式存在差异，这与rDNA位点的数量和分布一起，使得能够对这里研究的所有物种进行特征描述。大量的染色体标记表明，三个根状茎四倍体物种构成一个自然群体，并且可能至少有一个共同的二倍体祖先。对所分析的二倍体物种的细胞遗传学数据表明，唯一的根状茎二倍体物种——布尔卡花生——具有与根状茎四倍体不同的核型模式，这表明它不太可能是四倍体的基因组供体，且根状花生组具有非单系性质。因此，四倍体物种应被排除在R基因组之外，R基因组应仅保留给布尔卡花生。相反，这些四倍体的核型特征与直立花生组和匍匐花生组的不同物种（E基因组物种）的核型特征相符，这暗示了这些四倍体多起源的假说。此外，还讨论了多倍体性质以及与四倍体更接近的二倍体物种组。
