Triticeae Dumort. is a tribe within the Pooideae subfamily of Poaceae. Major crop genera found in this tribe include barley (Hordeum), wheat (Triticum) and rye (Secale) all of which are closely related to each other. In Turkey, with the several subgroups, this tribe is represented by 16 genera and 75 species, many of which have great economic values. The main objective of this research work is to determine the taxa of this tribe on the basis of their diagnostic anatomical characters of vegetative organs for the recognision of genera, sections, species, and infraspecific categories. By using both fresh and herbarium specimens, transverse sections of vegetative organs were obtained by using two different sectioning methods. This study covers both qualitative anatomical characters, such as sclerenchyma position, hair density and intercellular cavities of roots, shapes of leaves, presence of midrib, occurrence of leaf hairs, shapes of girders or strands, arrangement of sclerenchyma around vascular bundles and arrangement of epidermal cells, cell wall undulations, appearance of silica bodies, type of bulliform cells, arrangement of culm vascular bundles and their connections to the epidermis, hollowness of culms, as well as quantitative characters, such as sclerenchyma line number of roots, vascular bundle line numbers and diameters of culms, sclerenchyma line number of leaf margins, line numbers and sizes of all types of costal leaf hairs, stomata and interstomatal cell lines. In conclusion, all these properties are useful to understand both systematics and evolutionary relationships of the taxa. Moreover, the leaves of the tribe have the most numerous diagnostic characters. The roots do not have central metaxylem. The metaxylem elements are scattered in the vascular cylinder. The internodular parts of the culms may be hollowed or solid. However, the nodular parts of the culms generally have the same structure. Furthermore, there are two species which can be assigned as a subtribe.

The Triticeae is one of the most important tribes of the family Poaceae. It contains wheat (Triticum L.), barley (Hordeum L.) and rye (Secale L.) which are economically the most important cereals. Although the tribe has been the focus of several systematic studies there has not been a universally accepted taxonomic treatment for the tribe. This research study aiming to revise the tribe Triticeae Dumort. (Poaceae) in Turkey has been carried out by means of collecting specimens from all the localities in Turkey as well as examining the material collected over the years by the other researchers either from Turkey or abroad for a 4 year period starting from June 1th, 2006. All the specimens belonging the tribe were analysed by means of using standart taxonomic methods. This thesis is divided into four main chapters. In the first and second chapters, an introduction and general information about the tribe Triticeae and the material and methods used in the study are given. In the introduction part different taxonomic treatments on the tribe are explained briefly and the recent studies on the genera included in the tribe such as taxonomical, morphological and cytological are explained breifly. In the third chapter of the thesis, the significance of the morphological, micromorphological and ecological data which were used as diagnostic features in the taxonomy of the tribe are explained. Especially, SEM surveys of the glumes and lemma parts found to have great taxonomic values for the systematics of tribe. Distribution and habitat preferences of the tribe are discussed and IUCN threat categories of the taxa are reevaluated along with the types of threats so as to guarantee their sustainability of the rare taxa in Turkey. The fourth chapter covers the revision of the Tribe Triticeae in Turkey. A key for the genera is given. Synonymy, updated descriptions, flowering time, habitat, type citation, general distribution in Turkey, phytogeographical elements, specimen citations on a grid basis and general distribution outside Turkey, are given for each species. Along with general descriptions, keys to species and infraspecific categories are where necessary. In Tribe Triticeae, 18 genera, 79 species, 27 subspecies and 37 varieties have been recognized including 1 new species (Psathyrostachys narmanica Cabi &amp / Dogan sp. nov.), 3 new subspecies (Psathyrostachys fragilis (Boiss.) Nevski subsp. artvinense Cabi &amp / Dogan subsp. nov. / P. daghestanica (Alex.) Nevski subsp erzurumica Cabi&amp / Dogan subsp. nov. / Aegilops triuncialis L. subsp bozdagensis Cabi&amp / Dogan subsp nov.) and 4 new varieties (Agropyron cristatum (L.) subsp. pectinatum (Bieb.) Tzvelev var. mucranatum var. nov. / Eremopyrum bonaepartis (Sprengel) Nevski. var. aristatum Cabi &amp / Dogan / Thinopyrum pycnanthum (Godr.) Barkworth var. aristatum Cabi &amp / Dogan var. nov. / Hordeum spontaneum C. Koch var. anatolicum Cabi &amp / Dogan var. nov. In addition to the taxa new for science, Aegilops juvenalis (Thell.) Eig. and Hordeum spontaneum var. proskowetzii N&aacute / b

Investigations into plant-pathogen interactions have provided us with several models underlying the genetic basis of host resistance in plants. In the past decade, tens of resistance genes have been isolated from numerous crop and model plant species and these form a few distinct classes when classified by domain structure, the majority being nucleotide-bindingsite- leucine-rich-repeat (NBS-LRR) genes. The NBS-LRR family consists of two sub-families based on the N-terminal domain: the coiled-coil (CC) NBS-LRRs and the Toll Interleukin Receptor homology domain (TIR) NBS-LRRs. The potential of these genes for future and current agricultural breeding programs has driven a large number of studies exploring the members of these gene families in the genomes of a variety of crop species. In the present study I focused on the NBS-LRR family in the allohexaploid wheat genome and obtained a comprehensive set of Triticeae NBS-LRR homologues using a combination of data-mining approaches. As starting point I detected conserved motifs in the dataset, finding all six previously characterized in the core-NBS domain of other plant NBS-LRRs. Phylogenetic analysis was performed to study relationships between the Triticeae NBS-LRR family and the 25 CC-NBS-LRR (CNL) R genes identified to date. I found the Triticeae CNL family to be highly divergent, containing ancient clade lineages, as seen in all angiosperm 120 taxa previously studied, and found a number of “ancient” dicotyl R genes grouped with Triticeae clades. The evolution of recent NBS-LRR gene duplications in the Triticeae was studied at the hand of two modes of duplication - firstly individual gene duplications yielding paralogous loci and secondly gene duplication by allopolyploidy. Current models of NBS-LRR family evolution predict that functional divergence occurs after gene duplication. An alternative is that divergence takes place at allele level, followed by a locus duplication that fixes heterozygosity in a single haplotype by unequal recombination. I investigated this hypothesis by studying the evolution of gene duplicates in two different contexts – paralogous duplications in the diploid barley genome and homeologous duplications in the allohexaploid genome of wheat. Nonsynonymous to synonymous substitution rate ratios were estimated for paralogous gene duplications in three recently diverged NBS-LRR clades. All pairwise comparisons yielded Ka:Ks ratios strongly indicative of purifying selection. Given that R gene mediated resistance is inherited qualitatively rather than quantitatively, I interpret this as evidence that even closely related paralogous copies (90-95% identity) should have independent recognition specificities maintained by purifying selection. Homeologous duplications were studied in allohexaploid wheat (AABBDD) using a section of the go35 NBS-LRR gene (2L) of the B and D diploid donor species of wheat. Numerous synonymous substitutions distinguished the B and D genome copies, with an absence of nonsynonymous substitutions. In contrast, single unique nonsynonymous substitutions were found in four out of five polyploid wheat go35 alleles, indicating that selection pressure was indeed relaxed across the homeolocus. Recent studies on polyploid genomes have shown that duplicated resistance genes are far more likely to be eliminated than highly transcribed genes such as tRNAs and rRNAs. These results are in agreement with the view that functional divergence takes place before duplication for NBS-LRR genes, as the loci duplicated by polyploidy appear not to evolve under purifying selection, as I found for the paralogous loci investigated. / Dissertation (MSc)--University of Pretoria, 2008. / Genetics / unrestricted

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