Genetic and sexual separation between insect resistant and susceptible Barbarea vulgaris plants in Denmark.

Co-evolution between herbivores and plants is believed to be one of the processes creating Earth's biodiversity. However, it is difficult to disentangle to what extent diversification is really driven by herbivores or by other historical-geographical processes like allopatric isolation. In the cruciferous plant Barbarea vulgaris, some Danish individuals are resistant to herbivory by flea beetles (Phyllotreta nemorum), whereas others are not. The flea beetles are, in parallel, either resistant or susceptible to the plants defenses. To understand the historical-evolutionary framework of these interactions, we tested how genetically divergent resistant and susceptible plants are, using microsatellite markers. To test whether they are reproductively fully compatible, resistant and susceptible plants were grown intermixed in an outdoor experiment, and the paternity of open-pollinated offspring was determined by analysis of molecular markers. Resistant and susceptible Danish plants were genetically strongly differentiated and produced significantly fewer hybrids than expected from random mating or nearest neighbour mating. Our results suggest that the two types belong to different evolutionary lineages that have been (partly) isolated at some time, during which genetic and reproductive divergence evolved. A parsimonious scenario could be that the two plant types were isolated in different refugia during the previous ice age, from which they migrated into and met in Denmark and possibly neighbouring regions. If so, resistance and susceptibility has for unknown reasons become associated with the different evolutionary lineages.

The genomic organization and evolutionary distribution of a tandemly repeated DNA sequence family in the genus Crocus (Iridaceae).

From a recombinant DNA-library from Crocus vernus, two closely related clones of highly repetitive DNA, pCvKB7 and pCvKB8, were sequenced and their genomic distribution and organization were investigated by Southern and in situ hybridization. The lengths of the clones were 181 and 178 bp respectively; the sequences were approximately 85% identical, and thus belonged to a sequence family, named the pCvKB8-family. No homologous sequences were found in the databases (BLAST made may 2004). The presence of pCvKB8 in 52 Crocus species and six species from other genera were analyzed by Southern hybridization. The sequence family was essentially Crocus-specific. However, the distribution of hybridization signal across the genus showed poor agreement with the taxonomic structure of the Crocus genus, suggesting that the subdivision does not follow the phylogeny of this sequence family. The chromosomal distribution on three Crocus species was essentially identical: tandem organization close to all telomeres and most centromeres, with a few additional intercalary sites.

Genome discrimination by in situ hybridization in Icelandic species of Elymus and Elytrigia (Poaceae: Triticeae).

The genome constitution of Icelandic Elymus caninus, E. alaskanus, and Elytrigia repens was examined by fluorescence in situ hybridization using genomic DNA and selected cloned sequences as probes. Genomic in situ hybridization (GISH) of Hordeum brachyantherum ssp. californicum (diploid, H genome) probe confirmed the presence of an H genome in the two tetraploid Elymus species and identified its presence in the hexaploid Elytrigia repens. The H chromosomes were painted uniformly except for some chromosomes of Elytrigia repens which showed extended unlabelled pericentromeric and subterminal regions. A mixture of genomic DNA from H. marinum ssp. marinum (diploid, Xa genome) and H. murinum ssp. leporinum (tetraploid, Xu genome) did not hybridize to chromosomes of the Elymus species or Elytrigia repens, confirming that these genomes were different from the H genome. The St genomic probe from Pseudoroegneria spicata (diploid) did not discriminate between the genomes of the Elymus species, whereas it produced dispersed and spotty hybridization signals most likely on the two St genomes of Elytrigia repens. Chromosomes of the two genera Elymus and Elytrigia showed different patterns of hybridization with clones pTa71 and pAes41, while clones pTa1 and pSc119.2 hybridized only to Elytrigia chromosomes. Based on FISH with these genomic and cloned probes, the two Elymus species are genomically similar, but they are evidently different from Elytrigia repens. Therefore the genomes of Icelandic Elymus caninus and E. alaskanus remain as StH, whereas the genomes of Elytrigia repens are proposed as XXH.

Unifying plant molecular data and plants.

Located at a botanical department at an Agricultural University, our taxonomical and genetic research is mainly directed towards cultivated plants and their wild relatives. The investigations are usually under a common heading 'experimental taxonomy', and include basic systematics, cytogenetics, biodiversity, population dynamics, conservation and evolutionary questions correlating the wild species and the cultivated forms. Our point of initiation is the plants and questions/problems raised regarding these plants. Our way of approaching the problems is usually by applying different sets of data and testing them. Experimental taxonomy covers classical cytogenetics (chromosome counting and karyotyping) as well as molecular cytogenetic methods (RAPD, RFLP, in situ hybridization), and includes also chemical data on isoenzymes and anthocyanins. We have had good collaborations with other laboratories and found their expertise on the plants in question very helpful. The aim is always to unify various data on the same set of problems, in order to get a more complete understanding of the plants. At present the department is working on several, quite different plant genera, comprising herbs, aquatic plants, and trees. The methods vary, depending on the plants and the problems in question. Some of the current investigations concern the horticultural genera Lilium and Crocus, in which the main point of interest is the study of chromosome evolution using fluorescence in situ hybridization; preliminary investigations into the composition of anthocyanins in Crocus look very promising. In the tropical starch tuber crop Pachyrhizus (Fabaceae), molecular analyses of relationships between existing cultivars, landraces and wild material have been carried out. A genus which we, in cooperation with a number of other laboratories, have been working with for many years is Hordeum (Poaceae) with one cultivated species (barley) and 31 wild species. Here the main areas of investigation have been field studies and collecting, followed by a taxonomical treatment, hybridization experiments, cytogenetic analysis and isoenzyme studies. Within the field of forestry, we have used population genetics as a tool in the management of natural and domesticated populations and for conservation of genetic diversity. We have also ventured into the identification and use of DNA markers that are suited for genome mapping in Picea abies (Norway Spruce).