Allopolyploid Origin of Chenopodium album s. str. (Chenopodiaceae): A Molecular and Cytogenetic Insight

Abstract

Reticulate evolution is characterized by occasional hybridization between two species, creating a network of closely related taxa below and at the species level. In the present research, we aimed to verify the hypothesis of the allopolyploid origin of hexaploid C. album s. str., identify its putative parents and estimate the frequency of allopolyploidization events. We sampled 122 individuals of the C. album aggregate, covering most of its distribution range in Eurasia. Our samples included putative progenitors of C. album s. str. of both ploidy levels, i.e. diploids (C. ficifolium, C. suecicum) and tetraploids (C. striatiforme, C. strictum). To fulfil these objectives, we analysed sequence variation in the nrDNA ITS region and the rpl32-trnL intergenic spacer of cpDNA and performed genomic in-situ hybridization (GISH). Our study confirms the allohexaploid origin of C. album s. str. Analysis of cpDNA revealed tetraploids as the maternal species. In most accessions of hexaploid C. album s. str., ITS sequences were completely or nearly completely homogenized towards the tetraploid maternal ribotype; a tetraploid species therefore served as one genome donor. GISH revealed a strong hybridization signal on the same eighteen chromosomes of C. album s. str. with both diploid species C. ficifolium and C. suecicum. The second genome donor was therefore a diploid species. Moreover, some individuals with completely unhomogenized ITS sequences were found. Thus, hexaploid individuals of C. album s. str. with ITS sequences homogenized to different degrees may represent hybrids of different ages. This proves the existence of at least two different allopolyploid lineages, indicating a polyphyletic origin of C. album s. str.

Human‐mediated dispersal of weed species during the Holocene: A case study of Chenopodium album agg.

“…The results of the present study further corroborate those of Krak et al. (), showing that not only C. betaceum ( C. strictum auct.) and C. striatiforme but also C. novopokrovskyanum may have been involved as putative tetraploid parents of hexaploid taxa.…”

“…has already been demonstrated by Krak et al. (). They distinguished several rDNA ribotypes within this species, two of these were also found in tetraploids.…”

“…Nevertheless, the number of shared haplotypes between the tetraploid and hexaploid taxa indicates that the number of independent origins of the hexaploid taxa is probably higher than two, as was found by Krak et al. ().…”

“…and C. striatiforme but also C. novopokrovskyanum may have been involved as putative tetraploid parents of hexaploid taxa. Nevertheless, the number of shared haplotypes between the tetraploid and hexaploid taxa indicates that the number of independent origins of the hexaploid taxa is probably higher than two, as was found by Krak et al (2016).…”

“…The origins of the cpDNA clade “C” hexaploids via hybridisation of clade “C” tetraploid and clade “A” or “B” diploid species have already been confirmed (Krak et al., ; Mandák et al., , ). In this study, we found seven haplotypes shared among tetra‐ and hexaploid taxa (Figure ).…”