The subdivision found with FISH is consistent with the clades recovered with cpDNA data and both analyses suggest that the Quadrifaria group, as presently defined, is not monophyletic and its species belong in at least two clades.

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Wild potato relatives are rich sources of desirable traits for introgressive hybridisation into cultivated potato. One of them, Solanum commersonii (2n = 2x = 24, 1EBN, endosperm balance number), is an important species belonging to the potato tertiary genepool. It can be used in potato breeding through bridge crosses and 2n gamete production. Triploid F 1 hybrids between S. commersonii (through spontaneous 2n egg formation) and diploid 2EBN Solanum tuberosum Group Phureja were crossed with S. tuberosum Group Tuberosum, resulting in successive backcross 1, 2 and 3 progenies. The main aim of this study was to determine if there are any barriers to homoeologous pairing and recombination in the allotriploid (S. commersonii 9 potato) hybrids and their backcrosses, and so to predict if S. commersonii chromosomes can be transmitted to the next generation and introgressed into their recipient potato chromosomes. Microscopic observations of spread pollen mother cells suggested no preferential pairing in the triploid hybrids, while chromosome transmission and segregation in further meiotic stages were fairly balanced. Fluorescent in situ hybridisation with BAC probes (BAC FISH) was used to obtain markers to trace the meiotic behaviour of specific chromosome pairs. Moreover, genomic in situ hybridisation (GISH) demonstrated no obvious differences in fluorescence signals between the homoeologues suggesting that repetitive sequences did not diverge much between the parental species. As a consequence, we were not able to trace the course of the S. commersonii chromosomes in the successive introgressive hybridisation backcross generations. Our results strongly point at a high genomic similarity between the homoeologous chromosomes promising high suitability of S. commersonii in introgressive hybridisation breeding of potato.

Many Achyrocline (Asteraceae, tribe Gnaphalieae) species are widely used in Argentina, Brazil and Uruguay as popular medicinal and aromatic plants. Achyrocline flaccida, A. satureioides, A. alata, and A. crassiuscula are distributed in Uruguay and popularly known as ‘marcelas’. In order to characterize them, we performed chromosome counts, compared the karyotypes, mapped the 5S and 45S rDNA sites by fluorescent in situ hybridization, and estimated their DNA content. All species were diploid with 2n = 28 chromosomes, this being the first report for A. flaccida and A. crassiuscula. All species showed symmetrical karyotypes composed exclusively of biarmed chromosomes. DNA content estimated by flow cytometry revealed 2C values ranging from 5.73 to 6.03 pg, the amounts for A. alata and A. crassiuscula being higher than those for the other species. Cytogenetic mapping of 5S and 45S rDNA sequences in three species, A. flaccida, A. satureioides and A. alata, showed that in these species both sites co-localized in the pericentromeric region of chromosome 10. This site corresponds to the only DAPI^– and CMA⁺ band of their genomes. Southern blot hybridization of 5S and 45S rDNA on BamHI digested genomic DNA confirmed the tight linkage of these rDNA families into a single unit. Cytological data indicate that Achyrocline species are karyologically poorly differentiated, whereas the uncommon distribution of 5S and 45S rDNA suggests a close relationship with other genera of the Anthemidae tribe.

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