Comparison of ribosomal DNA Sequences of Dactylis taxa by Fluorescent In Situ Hybridization Tecnique

The basic knowledge of polyploidy and genome structures belonging to many species of perennial forage grasses is incomplete or absent. In order to determine and apply appropriate strategies in these breeding activities, it is necessary to know these basic information. In allogamic genera which contain a large number of ecotypes with different levels of polyploidy, such as Dactylis L., another problem is that their chromosome are morphologically similar and small, making it difficult to identify and correctly matched to their homologues. Therefore, the karyotype analyzes performed on Dactylis by classical cytogenetic methods to date have not provided the expected benefits in analyzing the genomes of Dactylis taxa and determining the relationships between them. Fluorescent in situ hybridization (FISH) technique is one of the advanced techniques of cytogenetics and is a very useful and novel method for determining the physical locations of specific DNA sequences on chromosomes. The aim of this thesis is to provide new information, for the first time, about Dactylis genome and its organization by using the 5S and 25S rDNA sequences which commonly used as probes. By using FISH technique, the distribution of rDNA regions of taxa on number and mitotic chromosomes was tried to be determined and it was aimed to obtain the karyotypes of sensitivity which could be useful in the analysis and relations of Dactylis genomes, and to match the identification and homologs of chromosomes. In the study, quality and quantity of cytological examinations for 2 years from approximately 9 diploids and 31 tetrapoliploids from gene banks of research institutes such as IPK (Gaterslaben, Germany), IBER (Aberystwyth, England), Western Regional Plant Introduction Station (Pulmann, Washington, USA) were used. According to FISH results, diploids Dactylis was determined to have 8 and 10 rDNA signals in total. The number of 25S rDNA signals of diploids were observed 4 and 6, and the number of 5S rDNA signals were observed 2 and 4. In tetrapoliploids Dactylis, the total number of rDNA signals varied between 12 and 18. In tetrapoliploids Dactylis were determined 25S rDNA signals between 8 and 14, 5S rDNA signals between 4 and 6. In addition two triploid taxa were found to have 9 and 11 rDNA signals, respectively. According to the 5S and 25S rDNA signal characteristics, it is understood that intraspecifity is high in Dactylis genus, polyploidization occurs, autopolyploidization and segmental autopolyploidization cases could be mentioned. Key Words: Dactylis, FISH, rDNA, Genome analysis, karyotype, Polyploidy