Analysis of Genetic Diversity of Spring Durum Wheat (<Emphasis Type="Italic">Triticum durum</Emphasis> Desf.) Cultivars Released in Russia in 1929–2004

Based on genealogical analysis, the genetic diversity of 78 spring durum wheat cultivars released in Russia in 1929–2004 have been examined. The temporal trends of change in diversity were studied using series of n × m matrices (where n is the number of the cultivars and m is the number of original ancestors) and calculating coefficients of parentage in sets of cultivars released in particular years. The pool of original ancestors of spring durum wheat cultivars includes 90 landraces and old varieties, more than a half (57%) of which originate from European countries, including Russia and Ukraine (45%). The original ancestors strongly differ in the frequency of presence in the cultivar pedigrees. Landraces Beloturka, Sivouska, Kubanka (T. durum Desf.), Transbaikalian emmer, Yaroslav emmer (T. dicoccum Schuebl.), Poltavka (T. aestivum L.), and the original ancestors of cultivars Kharkov 46, Narodnaya, and Melanopus 1932 enter in the pedigrees of more than half of cultivars created within the framework of various breeding programs. At that, their distribution by cultivars from different breeding centers strongly varies. Analysis of temporal dynamics of genetic diversity, based on genetic profiles and coefficients of parentage, has shown that the genetic diversity of Russian durum wheats increased during the period examined. Nevertheless, genetic erosion of the local material—a loss of approximately 20% of the pool of Russian original ancestors—has been found. The contribution of the original ancestors to the pedigrees of different cultivars, constructed in different breeding centers and recommended for cultivation in different regions, has been estimated. The variation of the released cultivars was highest in the Lower Volga region and lowest in the Ural region. In all, the lower threshold of genetic diversity in all regions does not reach the critical level, corresponding to the similarity of half-sibs. The set of modern cultivars included in the Russian Official List 2004 has a cluster structure.     

Allelic diversity at gliadin-coding gene loci in cultivars of spring durum wheat (<Emphasis Type="Italic">Triticum durum</Emphasis> Desf.) Bred in Russia and former Soviet republics in the 20th century

Allelic diversity at five gliadin-coding gene loci has been studied in the most important spring durum wheat cultivars released in Russia and former Soviet republics in the 20th century (66 cultivars). Seven, 5, 8, 13, and 2 allelic variants of blocks of gliadin components controlled by the loci Gli-A1 ^d , Gli-B1 ^d , Gli-A2 ^d , Gli-B2 ^d , and Gli-B5 ^d , respectively, have been identified. The allelic diversity did not exhibit a consistent trend during the period studied. Nei’s diversity index (H) was 0.68 in the period from 1929 to 1950, increased to 0.70 in 1951–1980, and decreased to 0.58 after the year 1981. It has been found that the most frequent alleles in this collection are relatively rare in other regions of the world, which suggests unique ways of the formation of the diversity of durum wheat cultivars in the former Soviet Union. The efficiency of electrophoresis of storage proteins as a method for identification of durum wheat cultivars by the gliadin electrophoretic pattern has been estimated.     

Analysis of genetic diversity of spring durum wheat (Triticum durum Desf.) cultivars released in Russia in 1929-2004

Based on genealogical analysis, the genetic diversity of 78 spring durum wheat cultivars released in Russia in 1929-2004 have been examined. The temporal trends of change in diversity were studied using series of n x m matrices (where n is the number of the cultivars and m is the number of original ancestors) and calculating coefficients of parentage in sets of cultivars released in particular years. The pool of original ancestors of spring durum wheat cultivars includes 90 landraces and old varieties, more than a half (57%) of which originate from European countries, including Russia and Ukraine (45%). The original ancestors strongly differ in the frequency of presence in the cultivar pedigrees. Landraces Beloturka, Sivouska, Kubanka (T. durum Desf.), Transbaikalian emmer, Yaroslav emmer (T. dicoccum Schuebl.), Poltavka (T. aestivum L.), and the original ancestors of cultivars Kharkov 46, Narodnaya, and Melanopus 1932 enter in the pedigrees of more than half of cultivars created within the framework of various breeding programs. At that, their distribution by cultivars from different breeding centers strongly varies. Analysis of temporal dynamics of genetic diversity, based on genetic profiles and coefficients of parentage, has shown that the genetic diversity of Russian durum wheats increased during the period examined. Nevertheless, genetic erosion of the local material-a loss of approximately 20% of the pool of Russian original ancestors-has been found. The contribution of the original ancestors to the pedigrees of different cultivars, constructed in different breeding centers and recommended for cultivation in different regions, has been estimated. The variation of the released cultivars was highest in the Lower Volga region and lowest in the Ural region. In all, the lower threshold of genetic diversity in all regions does not reach the critical level, corresponding to the similarity of half-sibs. The set of modern cultivars included in the Russian Official List 2004 has a cluster structure.     

Catalogue of alleles of gliadin-coding loci in durum wheat (Triticum durum Desf.)

Gliadins are seed storage proteins which are characterized by high intervarietal polymorphism and can be used as genetic markers. As a result of our work, a considerably extended catalogue of allelic variants of gliadin component blocks was compiled for durum wheat; 74 allelic variants for four gliadin-coding loci were identified for the first time. The extended catalogue includes a total of 131 allelic variants: 16 for locus Gli-A1(d), 19 for locus Gli-B1(d), 41 for locus Gli-A2(d), and 55 for locus Gli-B2(d). The electrophoretic pattern of the standard cultivar and a diagram are provided for every block identified. The number of alleles per family is quite small for loci Gli-A1(d) and Gli-B1(d) of durum wheat, as contrasted to loci Gli-A2(d) and Gli-B2(d) that are characterized by large families including many alleles. The presence of large block families determines a higher diversity of durum wheat for loci Gli-A2(d) and Gli-B2(d) as compared to Gli-A1(d) and Gli-B1(d). The catalogue of allelic variants of gliadin component blocks can be used by seed farmers to identify durum wheat cultivars and evaluate their purity; by breeders, to obtain homogenous cultivars and control the initial stages of selection; by gene bank experts, to preserve native varieties and the original biotypic composition of cultivars.     

Domesticated emmer wheat [T. turgidum L. subsp. dicoccon (Schrank) Thell.] as a source for improvement of zinc efficiency in durum wheat

Modern durum wheat (AABB) is more sensitive to zinc (Zn) deficiency than bread wheat (AABBDD). One strategy to increase productivity and expansion of durum wheat industry in Zn-deficient soils is to improve its ability to grow and yield in such soils. This ability is termed Zn efficiency. In a growth room experiment using soil culture, we assessed the potential of Triticum turgidum L. subsp. dicoccon (Shrank) Thell. (domesticated emmer wheat, AABB) as a genetic resource for further improvement of Zn efficiency in modern durum wheat. Twenty four accessions of domesticated emmer wheat, four durum landraces/cultivars, and two bread wheat cultivars/ advanced breeders lines of known Zn efficiency were tested under Zn deficiency and Zn sufficiency. Significant variation was observed among genotypes in Zn deficiency symptoms, dry matter production, shoot Zn concentration, shoot Zn content and Zn utilisation efficiency (physiological efficiency). We identified domesticated emmer wheat accessions with greater Zn efficiency than modern durum wheat and even bread wheat genotypes. These accessions could be used in breeding programs to improve Zn efficiency of durum wheat. The results suggest that Zn efficiency of durum or bread wheat is likely to be determined collectively by its progenitors.     

Allelic reduction and genetic shift in the Canadian hard red spring wheat germplasm released from 1845 to 2004

Analysis of genetic diversity changes in existing gene pools of cultivated crops is important for understanding the impact of plant breeding on crop genetic diversity and developing effective indicators for genetic diversity of cultivated plants. The objective of this study was to assess genetic diversity changes in 75 Canadian hard red wheat (Triticum aestivum L.) cultivars released from 1845 to 2004 using 31 simple sequence repeats (SSRs) markers. A total of 267 SSR alleles were detected, and their allelic frequencies ranged from 0.01 to 0.97, with an average of 0.14. Significant allelic reduction was observed at only four SSR loci for the cultivars released from 1970 onwards. However, 51 alleles (about 19%) present in pre-1910 cultivars were undetected in cultivars released after 1990 and were spread over 27 SSR loci. The proportion of SSR variation accounted for by six breeding periods was 12.5%, by four ancestral families, 16.5%, and by eight breeding programs, 8.4%. The average genetic diversity measured by three different band-sharing methods did not change significantly among cultivars released from different breeding periods, breeding programs, and ancestral families. However, genetic shift was obvious in the cultivars released over the six breeding periods, reflecting well the various breeding efforts over years. These results clearly show the allelic reduction and genetic shift in the Canadian hard red spring wheat germplasm released over time. Consequently, more effort needs to be made to broaden the wheat breeding base and conserve wheat germplasm.     

Molecular markers as a complementary tool in risk assessments: quantifying interspecific gene flow from triticale to spring wheat and durum wheat

Triticale is being considered as a bioindustrial crop in Canada using genetic modification. Because related spring wheat (Triticum aestivum) and durum wheat (T. durum) may exhibit synchronous flowering and grow in proximity, determination of interspecific gene flow when triticale is the pollen donor is necessary to evaluate potential risk. Pollen-mediated gene flow risk assessments generally rely on phenotypic markers to detect hybridization but DNA markers could be powerful and less ambiguous in quantifying rare interspecific gene flow. Six cultivars representing four species [spring wheat, durum wheat, triticale and rye (Secale cereale)] were screened with 235 spring wheat and 27 rye SSR markers to evaluate transferability and polymorphism. Fifty-five polymorphic markers were used in conjunction with morphological characterization to quantify interspecific gene flow from a blue aleurone (BA) triticale line to two spring wheat cultivars (AC Barrie and AC Crystal) and one durum wheat cultivar (AC Avonlea). Approximately 1.9 Million seeds from small plot experiments were visually screened in comparison with known hybrid seed. In total 2031 putative hybrids were identified and 448 germinated. Morphological analysis of putative hybrid plants identified five hybrids while molecular analysis identified 11 hybrids and two were common to both. Combined, 14 hybrids were confirmed: 10 spring wheat × triticale (0.0008 % of harvested seed): seven AC Barrie × BA triticale (0.001 %) and three AC Crystal × BA triticale (0.0005 %); and four durum wheat × triticale (0.0006 %). The occurrence of rare hybrids does not present a substantial risk to the development of GM triticale.     

Microsatellite analysis reveals a progressive widening of the genetic basis in the elite durum wheat germplasm

It has been argued that the level of genetic diversity in the modern durum wheat (Triticum turgidum L. var. durum) elite germplasm may have declined due to the high selection pressure applied in breeding programs. In this study, 58 accessions covering a wide spectrum of genetic diversity of the cultivated durum wheat gene pool were characterized with 70 microsatellite loci (or simple sequence repeats, SSRs). On average, SSRs detected 5.6 different allelic variants per locus, with a mean diversity index (DI) equal to 0.56, thus revealing a diversity content comparable to those previously observed with SSRs in other small-grain cereal gene pools. The mean genetic similarity value was equal to 0.44. A highly diagnostic SSR set has been identified. A high variation in allele size was detected among SSR loci, suggesting a different suitability of these loci for estimating genetic diversity. The B genome was characterized by an overall polymorphism significantly higher than that of the A genome. Genetic diversity is organised in well-distinct sub-groups identified by the corresponding foundation-genotypes. A large portion (92.7%) of the molecular variation detected within the group of 45 modern cvs was accounted for by SSR alleles tracing back to ten foundation-genotypes; among those, the most recent CIMMYT-derived founders were genetically distant from the old Mediterranean ones. On the other hand, rare alleles were abundant, suggesting that a large number of genetic introgressions contributed to the foundation of the well-diversified germplasm herein considered. The profiles of recently released varieties indicate that the level of genetic diversity present in the modern durum wheat germplasm has actually increased over time.Communicated by F. Salamini     

Genetic Diversity and Population Structure of Tetraploid Wheats (Triticum turgidum L.) Estimated by SSR,DArT and Pedigree Data

Levels of genetic diversity and population genetic structure of a collection of 230 accessions of seven tetraploid Triticum turgidum L. subspecies were investigated using six morphological, nine seed storage protein loci, 26 SSRs and 970 DArT markers. The genetic diversity of the morphological traits and seed storage proteins was always lower in the durum wheat compared to the wild and domesticated emmer. Using Bayesian clustering (K = 2), both of the sets of molecular markers distinguished the durum wheat cultivars from the other tetraploid subspecies, and two distinct subgroups were detected within the durum wheat subspecies, which is in agreement with their origin and year of release. The genetic diversity of morphological traits and seed storage proteins was always lower in the improved durum cultivars registered after 1990, than in the intermediate and older ones. This marked effect on diversity was not observed for molecular markers, where there was only a weak reduction. At K >2, the SSR markers showed a greater degree of resolution than for DArT, with their identification of a greater number of groups within each subspecies. Analysis of DArT marker differentiation between the wheat subspecies indicated outlier loci that are potentially linked to genes controlling some important agronomic traits. Among the 211 loci identified under selection, 109 markers were recently mapped, and some of these markers were clustered into specific regions on chromosome arms 2BL, 3BS and 4AL, where several genes/quantitative trait loci (QTLs) are involved in the domestication of tetraploid wheats, such as the tenacious glumes (Tg) and brittle rachis (Br) characteristics. On the basis of these results, it can be assumed that the population structure of the tetraploid wheat collection partially reflects the evolutionary history of Triticum turgidum L. subspecies and the genetic potential of landraces and wild accessions for the detection of unexplored alleles.     

Quantifying relationships between rooting traits and water uptake under drought in Mediterranean barley and durum wheat

In Mediterranean regions drought is the major factor limiting spring barley and durum wheat grain yields. This study aimed to compare spring barley and durum wheat root and shoot responses to drought and quantify relationships between root traits and water uptake under terminal drought.One spring barley（Hordeum vulgare L. cv. Rum） and two durum wheat Mediterranean cultivars（Triticum turgidum L. var durum cvs Hourani and Karim） were examined in soil‐column experiments under well watered and drought conditions. Root system architecture traits, water uptake, and plant growth were measured. Barley aerial biomass and grain yields were higher than for durum wheat cultivars in well watered conditions. Drought decreased grain yield more for barley（47%） than durum wheat（30%, Hourani）. Root‐to‐shoot dry matter ratio increased for durum wheat under drought but not for barley, and root weight increased for wheat in response todrought but decreased for barley. The critical root length density（RLD） and root volume density（RVD） for 90% available water capture for wheat were similar to（cv. Hourani） or lower than（cv. Karim） for barley depending on wheat cultivar. For both species, RVD accounted for a slightly higher proportion of phenotypic variation in water uptake under drought than RLD.     

AFLP and pedigree-based genetic diversity estimates in modern cultivars of durum wheat [ Triticum turgidum L. subsp. durum (Desf.) Husn.

A substantial amount of between and within cultivar genetic variation was detected in all the 13 registered modern Canadian durum wheat (Triticum turgidum L. ssp. durum (Desf.) Husn.) cultivars based upon amplified restriction fragment polymorphism (AFLP). Of the approximately 950 detected AFLP markers, only 89 were polymorphic, with 41 between cultivars whereas the remaining 48 showed polymorphism within at least one cultivar. The ancestry of Canadian durum wheat cultivars was traced back to 125 cultivars, selections, and breeding lines including 17 landraces. Mean pair-wise genetic distance based on the kinship coefficient was 0.76. On the other hand, AFLP-based mean pair-wise genetic distance was 0.40. Even though there was a large difference between the means of the two diversity measures, a moderate positive correlation (r=0.457, p<0.002) was detected between the two distance matrices. Cluster analysis with the entire AFLP data divided all cultivars into three major groups reflecting their breeding origins. One group contained ’Pelissier’ alone, which was a selection from a landrace introduced into the US from Algeria. On the other hand such groupings among cultivars were not evident when KIN was used for genetic diversity measures instead. The level of genetic variation among individuals within a cultivar at the breeders’ seed level was estimated based on an inter-haplotypic distance matrix derived from the AFLP data. We found that the level of genetic variation within the most-developed cultivars is fairly substantial despite rigorous selection pressure aimed at cultivar purity in breeding programs. Comparison of AFLP and pedigree-based genetic diversity estimates in crop species such as durum wheat can provide important information for plant improvement. Received: 26 January 2001 / Accepted: 31 May 2001     

Genetic Diversity and Variation Among Botanical Varieties of Old Portuguese Wheat Cultivars Revealed by ISSR Assays

Inter-simple sequence repeats (ISSRs) were used for genetic diversity analyses of an Old Portuguese wheat collection. Eighteen primers produced 96.3 and 98.5% of ISSR polymorphism in bread and durum wheat cultivars, respectively. The unweighted pair group method with arithmetical averages (UPGMA) phenogram clearly split all cultivars based on their species/ploidy, reflecting a defined genetic structure. ISSRs revealed high genetic diversity at interspecific, intraspecific, and intercultivar levels. Thirty-three exclusive ISSR markers were found. Cultivars were clustered according to their botanical varieties and, in a few cases, with their homonym(s). No statistically significant differences were found between genetic diversity parameters of durum and bread wheat, probably due to high intraspecific diversity. Similar analyses were performed among botanical varieties, and their relationships were defined. Cladograms resembled UPGMA clustering. This highly genetically diverse Old wheat collection will be conserved and maintained, and it could be further used in breeding programs to widen the narrow genetic basis of modern wheat varieties and to avoid the loss of rare and unique alleles.     

Genetic Diversity in Old Portuguese Durum Wheat Cultivars Assessed by Retrotransposon-Based Markers

Retrotransposon-based markers, such as the inter-retrotransposon-amplified polymorphism (IRAP) and the retrotransposon microsatellite-amplified polymorphism (REMAP) are highly informative, multilocus, and reveal insertional polymorphisms among plant individuals. These markers have been used for evolutionary studies, genetic diversity assessment, DNA fingerprinting, genetic mapping linkage, and for the detection of genetic rearrangements induced by polyploidization. In this study, we used IRAP and REMAP markers to assess the genetic diversity among 51 old Portuguese durum wheat cultivars belonging to 27 botanical varieties and to define their genetic relationships. Five IRAP and four REMAP primer combinations were used. IRAP markers revealed 66.3% of polymorphism and an average of 18.4 bands per primer combination which ranged in size from 450 to 3,100?bp. The REMAP technique allowed the detection of 86.36% of inter-cultivar polymorphism and an average of 11 bands per primer combination. The molecular weight of the REMAP bands ranged from 250 to 2,750?bp. The durum wheat cultivars analyzed here belong to 27 botanical varieties of the subspecies Triticum turgidum subsp. turgidum L. [syn. T. turgidum] and Triticum turgidum L. subsp. durum [syn. T. durum] (Desf.) Husn.. Our results showed that the genetic variability assessed by both the IRAP and REMAP markers did not allow the clustering of the durum wheat cultivars according to their taxonomical criteria (subspecies or botanical variety) or homonymy. Nonetheless, these markers were useful for the assessment of genetic diversity at the individual level, for the definition of genetic relationships among cultivars, and for estimation of the genetic structure of the Old collection under analysis. The achieved data could be valuable for future experiments of DNA fingerprinting, genetic improvement, and germplasm conservation in wheat.     

Trends in Genetic Diversity Change of Spring Bread Wheat Cultivars Released in Russia in 1929–2003

Using genealogy analysis, we studied genetic diversity of 340 cultivars of spring bread wheat that were released on the territory of Russia in 1929–2003. Trends in the temporal change of genetic diversity were inferred from analysis of a set of n × m matrices, where n is the number of the released cultivars and m is the number of original ancestors. The pool of original ancestors of the spring bread wheat cultivars for the total period of study included 255 landraces, of which 88 were from the former USSR and modern Russia. The original ancestors showed great differences in their presence in the cultivar sets examined and, consequently, in their importance for the gene pool of Russian spring wheats. The distributions of contributions of dominant original ancestors to cultivar diversity were significantly different in different regions, indicating that the ancestors were specific for the cultivation conditions. During the last 75 years, the genetic diversity of the spring bread wheat cultivars has been increasing owing to the wide use of foreign material in Russian breeding programs. However, our analysis showed that about 60 landraces, including the Russian ones, were lost during the studied time period. The lost part makes up 35% of the gene pool of the Russian original ancestors. It is reasonable to assume that the lost landraces carried a gene complex f or adaptation to specific Russian environments. Specificity of the contributions of the original ancestors in the sets of cultivars produced in different breeding centers was established. A comparative analysis of genetic similarity of cultivars was carried out using coefficients of parentage. Significant differences in this parameter between breeding institutes and regions of cultivation were revealed.     

Arbitrarily primed-PCR based diversity assessment reflects hierarchical groupings of Indian tetraploid wheat genotypes

Genetic diversity analysis using PCR with arbitrary decamer primers (RAPD — random amplified polymorphic DNA) was carried out in a set of 63 tetraploid wheat genotypes which comprised 24 durum landraces, 18 durum cultivars, nine dicoccum cultivars, ten less commonly cultivated species and two wild tetraploid species. The durum and dicoccum wheat genotypes are a part of the germplasm used in Indian tetraploid wheat breeding programs. A total of 206 amplification products were obtained with 21 informative primers, of which 162 were polymorphic. The highest degree of polymorphism was seen in the wild and less commonly cultivated species (68.9%). Durum released cultivars showed greater polymorphism (50.6%) than landraces (44.8%), while dicoccum cultivars showed a considerably low level of polymorphism (23.6%). Cluster analysis led to the separation of wild and cultivated genotypes, and among cultivated emmer wheat distinct groups were formed by the durum cultivars, durum landraces and dicoccum cultivars. The subgroupings of landraces had no relation to their geographical distribution. The durum cultivars formed subgroups based on common parentage in their pedigree. Among species, wild timopheevi wheat (T. araraticum) and its cultivated form (T. timopheevi) formed a distinct group distant from all other genotypes. The present study is a first attempt at determining the genetic variation in Indian tetraploid wheats at the molecular level. Received: 10 January 1999 / Accepted: 30 January 1999     

Wheat genetic diversity trends during domestication and breeding

It has been claimed that plant breeding reduces genetic diversity in elite germplasm which could seriously jeopardize the continued ability to improve crops. The main objective of this study was to examine the loss of genetic diversity in spring bread wheat during (1) its domestication, (2) the change from traditional landrace cultivars (LCs) to modern breeding varieties, and (3) 50 years of international breeding. We studied 253 CIMMYT or CIMMYT-related modern wheat cultivars, LCs, and Triticum tauschii accessions, the D-genome donor of wheat, with 90 simple sequence repeat (SSR) markers dispersed across the wheat genome. A loss of genetic diversity was observed from T. tauschii to the LCs, and from the LCs to the elite breeding germplasm. Wheats genetic diversity was narrowed from 1950 to 1989, but was enhanced from 1990 to 1997. Our results indicate that breeders averted the narrowing of the wheat germplasm base and subsequently increased the genetic diversity through the introgression of novel materials. The LCs and T. tauschii contain numerous unique alleles that were absent in modern spring bread wheat cultivars. Consequently, both the LCs and T. tauschii represent useful sources for broadening the genetic base of elite wheat breeding germplasm.     

Analysis of diversity of Russian and Ukrainian bread wheat (Triticum aestivum L.) cultivars for high-molecular-weight glutenin subunits

The allelic diversity of high-moleculat-weght glutenin subunits (H WIGS) in Russian and Ukrainian bread wheat cultivars was analyzed. The diversity of spring wheat cultivars for alleles of the Glu-1 loci is characterized by medium values of the polymorphism index (polymorphism information content, PlC), and in winter wheats it varies from high at the Glu-A1 locus to low at the Glu-D1 locus. The spring and winter cultivars differ significantly in the frequencies of alleles of the glutenin loci. The combination of the Glu-A1b, Glu-B1c, and Glu-D1a alleles prevails among the spring cultivars, and the combination of the Glu-A1a, Glu-B1c, and Glu-D1d alleles prevails among the winter cultivars. The distribution of the Glu-1 alleles significantly depends on the moisture and heat supply in the region of origin of the cultivars. Drought resistance is associated with the Glu-D1a allele in the spring wheat and with the Glu-B1b allele in the winter wheat. The sources of the Glu-1 alleles were identified in the spring and wheat cultivars. The analysis of independence of the distribution of the spring and winter cultivars by the market classes and by the alleles of the HMWGS loci showed a highly significant association of the alleles of three Glu-1 loci with the market classes in foreign cultivars and independence or a weak association in the Russian and Ukrainian cultivars. This seems to be due to the absence of a statistically substantiated system of classification of the domestic cultivars on the basis of their quality.     

Wheat domestication: lessons for the future

Wheat was one of the first crops to be domesticated more than 10,000 years ago in the Middle East. Molecular genetics and archaeological data have allowed the reconstruction of plausible domestication scenarios leading to modern cultivars. For diploid einkorn and tetraploid durum wheat, a single domestication event has likely occurred in the Karacadag Mountains, Turkey. Following a cross between tetraploid durum and diploid T.?tauschii, the resultant hexaploid bread wheat was domesticated and disseminated around the Caucasian region. These polyploidisation events facilitated wheat domestication and created genetic bottlenecks, which excluded potentially adaptive alleles. With the urgent need to accelerate genetic progress to confront the challenges of climate change and sustainable agriculture, wild ancestors and old landraces represent a reservoir of underexploited genetic diversity that may be utilized through modern breeding methods. Understanding domestication processes may thus help identifying new strategies.     

Trends in genetic diversity change of spring bread wheat cultivars released in Russia in 1929-2003

Using genealogy analysis, we studied genetic diversity of 340 cultivars of spring bread wheat that were released on the territory of Russia in 1929-2003. Trends in the temporal change of genetic diversity were inferred from analysis of a set of n x m matrices, where n is the number of the released cultivars and m is the number of original ancestors. The pool of original ancestors of the spring bread wheat cultivars for the total period of study included 255 landraces, of which 88 were from the former USSR and modern Russia. The original ancestors showed great differences in their presence in the cultivar sets examined and, consequently, in their importance for the gene pool of Russian spring wheats. The distributions of contributions of dominant original ancestors to cultivar diversity were significantly different in different regions, indicating that the ancestors were specific for the cultivation conditions. During the last 75 years, the genetic diversity of the spring bread wheat cultivars has been increasing owing to the wide use of foreign material in Russian breeding programs. However, our analysis showed that about 60 landraces, including the Russian ones, were lost during the studied time period. The lost part makes up 35% of the gene pool of the Russian original ancestors. It is reasonable to assume that the lost landraces carried a gene complex f or adaptation to specific Russian environments. Specificity of the contributions of the original ancestors in the sets of cultivars produced in different breeding centers was established. A comparative analysis of genetic similarity of cultivars was carried out using coefficients of parentage. Significant differences in this parameter between breeding institutes and regions of cultivation were revealed.     

Efficient Agrobacterium transformation of elite wheat germplasm without selection

A previously reported Agrobacterium tumefaciens transformation system that transformed wheat cultivar Fielder at high efficiency was shown to also transform eight out of nine Triticum aestivum (hexaploid wheat) cultivars tested and two Triticum turgidum (durum wheat) cultivars. Transformation efficiencies of these wheat lines ranged from 1.5 to 51 %. Included amongst this germplasm were elite Australian hexaploid wheat cultivars that are currently in commercial cultivation and two of these cultivars, Gladius and Westonia, were transformed at 32 and 45 % efficiency, respectively. Similar high transformation efficiencies were observed for durum wheat cultivars Kronos (51 %) and Stewart (26 %). This highly efficient transformation system was used to generate transgenic plants in the absence of selection and high heritability of unselected transgenes was observed. Selectable marker free transgenic wheat plants were produced at 3 % efficiency. These data demonstrate highly efficient Agrobacterium transformation of diverse wheat germplasm, including elite cultivars, which enables routine production of selectable marker free transgenics.