Abstract
BackgroundInterspecific hybridisation resulting in polyploidy is one of the major driving forces in plant evolution. Here, we present data from the molecular cytogenetic analysis of three cytotypes of Elytrigia ×mucronata using sequential fluorescence (5S rDNA, 18S rDNA and pSc119.2 probes) and genomic in situ hybridisation (four genomic probes of diploid taxa, i.e., Aegilops, Dasypyrum, Hordeum and Pseudoroegneria).ResultsThe concurrent presence of Hordeum (descended from E. repens) and Dasypyrum + Aegilops (descended from E. intermedia) chromosome sets in all cytotypes of E. ×mucronata confirmed the assumed hybrid origin of the analysed plants. The following different genomic constitutions were observed for E. ×mucronata. Hexaploid plants exhibited three chromosome sets from Pseudoroegneria and one chromosome set each from Aegilops, Hordeum and Dasypyrum. Heptaploid plants harboured the six chromosome sets of the hexaploid plants and an additional Pseudoroegneria chromosome set. Nonaploid cytotypes differed in their genomic constitutions, reflecting different origins through the fusion of reduced and unreduced gametes. The hybridisation patterns of repetitive sequences (5S rDNA, 18S rDNA, and pSc119.2) in E. ×mucronata varied between and within cytotypes. Chromosome alterations that were not identified in the parental species were found in both heptaploid and some nonaploid plants.ConclusionsThe results confirmed that both homoploid hybridisation and heteroploid hybridisation that lead to the coexistence of four different haplomes within single hybrid genomes occur in Elytrigia allopolyploids. The chromosomal alterations observed in both heptaploid and some nonaploid plants indicated that genome restructuring occurs during and/or after the hybrids arose. Moreover, a specific chromosomal translocation detected in one of the nonaploids indicated that it was not a primary hybrid. Therefore, at least some of the hybrids are fertile. Hybridisation in Triticeae allopolyploids clearly and significantly contributes to genomic diversity. Different combinations of parental haplomes coupled with chromosomal alterations may result in the establishment of unique lineages, thus providing raw material for selection.
Highlights
Interspecific hybridisation resulting in polyploidy is one of the major driving forces in plant evolution
After genomic in situ hybridisation (GISH), we observed identical hybridisation patterns in both analysed plants, which consisted of 21 St (Pseudoroegneria) + 7 H (Hordeum) + 7 D (Aegilops) + 7 V (Dasypyrum) chromosomes (Fig. 2a and c; Table 2)
GISH analysis of the latter hybrid revealed the presence of four haplomes within this nonaploid, which consisted of four chromosome sets from Pseudoroegneria, two chromosome sets from Agropyron, two chromosome sets from Thinopyrum and one chromosome set from Hordeum
Summary
Interspecific hybridisation resulting in polyploidy is one of the major driving forces in plant evolution. Hybridisation and polyploidisation are the major driving forces underlying plant evolution [1,2,3,4]. While hybridisation through genome merging may lead to the formation of new hybrid species, polyploidisation can stabilise hybrid breeding behaviour [5]. The formation of new hybridogenous species in sympatry requires the presence of reproductive barriers between the hybrid and its parents. In the absence of reproductive barriers, newly formed hybrids can backcross with one or both parental species and form hybrid swarms [6]. The newly formed hybrid possesses a novel combination of genomes, which can manifest improved or enhanced
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