The Dilatata group of Paspalum includes species and biotypes native to temperate South America. Among them, five sexual allotetraploids (x = 10) share the same IIJJ genome formula: P. urvillei Steud, P. dasypleurum Kunze ex Desv., P. dilatatum subsp. flavescens Roseng., B.R. Arrill. & Izag., and two biotypes P. dilatatum Vacaria and P. dilatatum Virasoro. Previous studies suggested P. intermedium Munro ex Morong & Britton and P. juergensii Hack. or related species as their putative progenitors and donors of the I and J genome, respectively, and pointed to a narrow genetic base for their maternal origin. It has not yet been established whether the various members of the Dilatata group are the result of a single or of multiple allopolyploid formations. Here, we aimed to study the evolutionary dynamics of rRNA genes after allopolyploidisation in the Dilatata group of Paspalum and shed some light into the genome restructuring of the tetraploid taxa with the same genome formula. We used double target fluorescence in situ hybridisation of 35S and 5S rDNA probes and sequenced the nrDNA internal transcribed spacer (ITS) region. A variable number of loci at the chromosome ends were observed for the 35S rDNA, from 2 to 6, suggesting gain and loss of sites. For the 5S rDNA, only one centromeric pair of signals was observed, indicating a remarkable loss after polyploidisation. All ITS sequences generated were near identical to the one found for P. intermedium. Although sequences showed a directional homogeneisation towards the putative paternal progenitor in all tetraploid species, the observed differences in the number and loss of rDNA sites suggest independent ongoing diploidisation processes in all taxa and genome restructuring following polyploidy.

中文翻译：

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二倍体化过程对雀稗（禾本科、禾本科）异源多倍体物种 5S 和 35S rDNA 序列的影响

雀稗的 Dilatata 组包括原产于南美洲温带的物种和生物型。其中，五个有性异源四倍体 (x = 10) 共享相同的 IIJJ 基因组公式：P. urvillei Steud、P. dasypleurum Kunze ex Desv.、P. dilatatum subsp.。苦参 Roseng., BR Arrill。& Izag.，以及两种生物型 P. dilatatum Vacaria 和 P. dilatatum Virasoro。以前的研究表明 P. intermedium Munro ex Morong & Britton 和 P. juergensii Hack。或相关物种分别作为 I 和 J 基因组的推定祖先和供体，并指出其母系起源的狭窄遗传基础。尚未确定 Dilatata 组的各个成员是单个还是多个异源多倍体形成的结果。这里，我们旨在研究雀稗 Dilatata 组异源多倍化后 rRNA 基因的进化动力学，并为具有相同基因组公式的四倍体分类群的基因组重组提供一些启示。我们使用了 35S 和 5S rDNA 探针的双靶荧光原位杂交，并对 nrDNA 内部转录间隔区 (ITS) 区域进行了测序。对于 35S rDNA，在染色体末端观察到不同数量的基因座，从 2 到 6，表明位点的获得和损失。对于 5S rDNA，仅观察到一对着丝粒信号，表明多倍化后显着损失。生成的所有 ITS 序列与为中间假单胞菌发现的序列几乎相同。尽管序列在所有四倍体物种中都表现出对推定父系祖先的定向同质化，