Polyploidy is a widespread phenomenon among higher plants and a major factor shaping the structure and evolution of plant genomes. The important ornamental chrysanthemum (Chrysanthemum indicum hybrid) possesses a hexaploid genome with 54 chromosomes and was classified based on its evolutionary origin and cytological methods as an allopolyploid. However, it is questionable whether cytological methods are sufficient to determine the type of ploidy, and there are more informative methods available based on molecular marker analyses. Therefore, we collected segregation data for 406 dominant molecular marker alleles [327 amplified fragment length polymorphism (AFLPs), 65 single-strand conformation polymorphism (SSCPs) and 14 microsatellites (EST-SSRs)] in a biparental F1 population of 160 individuals. We analyzed these data for the characteristics that differ between allopolyploids and autopolyploids, including the segregation ratio of each marker, the ratio of single-dose (SD) to multi-dose (MD) markers, the ratio of SD markers in coupling to those in repulsion and the banding patterns of the SSRs. Whereas the analysis of the segregation ratio of each polymorphic marker indicated disomic (13 markers) as well as hexasomic (eight markers) inheritance, the ratio of SD markers in coupling to those in repulsion was 1:0, which is characteristic of autopolyploids. The observed ratio of SD to MD markers was 0.67:0.33 which is significantly different to the expected segregation for auto- and allohexaploids. Furthermore, the three EST-SSR alleles were inherited in all possible combinations and were not independent of each other, as expected for fixed heterozygosity in allopolyploids. Combining our results with published cytological data indicates that cultivated chrysanthemums should be classified as segmental allohexaploids.

We developed 12 polymorphic microsatellite markers for the tetraploid halophyte Suaeda maritima (Chenopodiaceae). Population genetic parameters were estimated for three populations from different habitats (coastal and inland), using the program Tetrasat. Between two and 15 alleles per locus were observed. Mean expected heterozygosities (H(E) ) and Shannon-Wiener Diversity Indices (H') per locus and population ranged from zero to 0.852, and from zero to 2.990, respectively. The two inland populations were less diverse than the coastal one at most of the loci. All markers cross-amplified in the closely related Suaeda salsa, and all but one were transferable to Suaeda spicata and Suaeda salinaria.

In some plant genera that contain species with complex genomes, the level and type of ploidy are still unknown due to a lack of characterized reference species and contradictory results from genetic and cytogenetic studies. Herein, we present the analysis of the genome of garden dahlias using molecular markers; this species is one for which the genome ploidy has remained controversial. We generated simple-sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) data from two segregating populations of garden dahlias. The combined analysis of SSR marker segregation, the ratio of single-dose to multidose markers, the ratio of markers linked in coupling and repulsion, and map construction revealed a predominantly autooctoploid genome with a low degree of preferential pairing. This finding indicates that dahlias are segmental allooctoploids that originated from autotetraploid ancestral genomes. Our results demonstrate that marker analysis is a suitable method for ploidy analysis in nonmodel crops. Novel marker techniques, such as restriction site associated DNA, will make this analysis even more effective before whole genome sequencing can be realized for these crops.

We developed 11 polymorphic microsatellite markers for Spergularia media (Caryophyllaceae), a perennial halophyte of coastal salt meadows and continental areas of western Eurasia. The number of alleles per locus observed in a single population of 20 individuals from the German North Sea coast ranged from 3 to 20. Observed and expected heterozygosities ranged from 0.200 to 0.850 and from 0.278 to 0.936 respectively. Observed heterozygosities were lower than expected heterozygosities at all loci, presumably as a consequence of inbreeding. All markers cross-amplified in the closely related S. salina. Of these, nine were polymorphic in the heterologous species. Only two primer pairs generated PCR products in S. diandra.