Intraspecific diversity of durum wheat (Triticum durum Desf.): a unif ied classif ication

The Department of Wheat Genetic Resources of the All-Russian Research Institute of Plant Genetic Resources (VIR) had developed and published in 1979 a classification of the genus Triticum L., which is based on the genomic composition of species and the presence or absence of a number of main genes that govern the "classification" traits. The grounds have been laid by F. Körnicke and J. Percival, and supplemented by N.I. Vavilov and K.A. Flaksberger. The classification, which is most often referred to as the "Classification of Triticum by Dorofeev et al.", belongs to a number of the main modern classifications of the genus. This is the world's first standardized system that contains all known intraspecific (infraspecific) taxa of wild and cultivated wheat species. A detailed classification makes it possible to identify a wide variety of forms in the genus Triticum L. and its individual species, which is especially important for collections preserved in genetic seed banks. The use of the intraspecific classification of the genus Triticum L. greatly simplifies the identification of the VIR collection accessions introduced from various sources or checking accession identity after regeneration in the field. However, the direct use of such a voluminous classification meets several difficulties. Therefore, we propose a unified intraspecific classification of durum wheat, based on the description of only 16 main botanical varieties out of 131 described so far, which have complexes of morphological traits of the spike and kernel that occur most frequently in durum wheat collections. The remaining 115 botanical varieties, which have additional traits, get their name by the addition of the abbreviated Latin name of one or another additional trait to the main name. Having mastered this way of describing the morphological traits of accessions, any user can easily navigate oneself in the systematized intraspecific diversity of collections. The purpose of this work is to acquaint the reader with the intraspecific classification of durum wheat (Triticum durum Desf.) developed at VIR and to offer its simplified version, which is based on the identification of the main and additional morphological traits of the spike and kernel.

Molecular characterization of vernalization loci VRN1 in wild and cultivated wheats

BACKGROUND

Variability of the VRN1 promoter region of the unique collection of spring polyploid and wild diploid wheat species together with diploid goatgrasses (donor of B and D genomes of polyploid wheats) were investigated. Accessions of wild diploid (T. boeoticum, T. urartu) and tetraploid (T. araraticum, T. timopheevii) species were studied for the first time.

RESULTS

Sequence analysis indicated great variability in the region from -62 to -221 nucleotide positions of the VRN1 promoter region. Different indels were found within this region in spring wheats. It was shown that VRN1 promoter region of B and G genome can also contain damages such as the insertion of the transposable element.Some transcription factor recognition sites including hybrid C/G-box for TaFDL2 protein known as the VRN1 gene upregulator were predicted inside the variable region. It was shown that deletions leading to promoter damage occurred in diploid and polyploid species independently. DNA transposon insertions first occurred in polyploid species. At the same time, the duplication of the promoter region was observed in A genomes of polyploid species.

CONCLUSIONS

We can conclude that supposed molecular mechanism of the VRN1 gene activating in cultivated diploid wheat species T. monococcum is common also for wild T. boeoticum and was inherited by T. monococcum. The spring polyploids are not related in their origin to spring diploids. The spring T. urartu and goatgrass accessions have another mechanism of flowering activation that is not connected with indels in VRN1 promoter region. All obtained data may be useful for detailed insight into origin of spring wheat forms in evolution and domestication process.

A genetic framework for grain size and shape variation in wheat

Grain morphology in wheat (Triticum aestivum) has been selected and manipulated even in very early agrarian societies and remains a major breeding target. We undertook a large-scale quantitative analysis to determine the genetic basis of the phenotypic diversity in wheat grain morphology. A high-throughput method was used to capture grain size and shape variation in multiple mapping populations, elite varieties, and a broad collection of ancestral wheat species. This analysis reveals that grain size and shape are largely independent traits in both primitive wheat and in modern varieties. This phenotypic structure was retained across the mapping populations studied, suggesting that these traits are under the control of a limited number of discrete genetic components. We identified the underlying genes as quantitative trait loci that are distinct for grain size and shape and are largely shared between the different mapping populations. Moreover, our results show a significant reduction of phenotypic variation in grain shape in the modern germplasm pool compared with the ancestral wheat species, probably as a result of a relatively recent bottleneck. Therefore, this study provides the genetic underpinnings of an emerging phenotypic model where wheat domestication has transformed a long thin primitive grain to a wider and shorter modern grain.

Genotyping of the Q locus in wheat by a simple PCR-RFLP method

The Q locus located on the long arm of chromosome 5A is a key factor in evolution and widespread cultivation of domesticated wheat. The Q locus pleiotropically affects many agronomically important traits including threshability, glume shape and tenacity, rachis fragility and others. Genotyping of the Q locus based on the complex traits is ambiguous due to their multi-genetic control through interactions with the Q locus. To determine the Q locus genotype of wheat accessions possessing A genome, we developed a method based on polymerase chain reaction - restriction fragment length polymorphism (PCR-RFLP) analysis. The Q and q alleles were clearly distinguished by PCR-RFLP analysis at six conserved single nucleotide polymorphisms in common wheat and wild and cultivated einkorn, emmer and timopheevi wheat. The Q locus genotype of Triticum sinskajae, which is one of the einkorn wheat species and exhibits free-threshing trait, was determined to be qq as expected. This simple PCR-RLFP-based genotyping method should serve as a useful tool in studying the origin of Q and thus wheat evolution after domestication and the following widespread cultivation.