Distribution and diversity of Aegilops tauschii in Iran

The wide morphological variation of Aegilops tauschii has led to the distinction of different subspecies; a typical ssp. tauschii and a second ssp. strangulata. However some researchers pointed out the existance of the intermediate form among morphologically distinguished subspecies. Distribution, diversity and the relationship between different subspecies and the intermediate form were evaluated in the Iranian Ae. tauschii collection. This collection was classified to 15 different populations according to morphological similarities and the collecting origin of accessions. The highest variation was found in tauschii population of Golestan followed by tauschii populations of Gilan and Ardebill, whereas the lowest variation was observed in tauschii populations of central Iran. Two discriminant functions suggested that the length of rachis node and spikelet glume, particularly, the length/width ratios of these traits had the highest impact on identification of different forms. Mahalanobis distances (D ² ) between the two subspecies along with intermediate form on the multidimensional scaling plot showed that the intermediate form is more similar to ssp. tauschii than ssp. strangulata. Although, the diversity within the ssp. strangulata was not very high, it widely affected the diversity of Iranian accessions of Ae. tauschii through continues crossing with the more diversed subspecies, tauschii, during thousands of years. This fact had lead to expansion of its distribution from its origin to Northern Khorasan, Northern Semnan and Eastern Ardebill by producing the intermediate form.     

Stripe rust resistance in <Emphasis Type="Italic">Aegilops tauschii</Emphasis> and its genetic analysis

Aegilops tauschii Coss., the D-genome progenitor of common wheat (Triticum aestivum L.) includes two subspecies, tauschii and strangulata (Eig) Tzvel. Subspecies tauschii has a wide geographic distribution spreading westwards to Turkey and eastwards to Afghanistan and China, while ssp. strangulata has a narrower distribution occurring only in two disjoined regions, southeastern Caspian Iran and Transcaucasia. A collection of 56 Ae. tauschii accessions was screened at adult stage against a mixture of pathotypes of stripe rust prevalent in the current wheat production in China. The results for three crop seasons indicated that among the 38 ssp. tauschii accessions, 37 were susceptible and only one was resistant, while all the 18 ssp. strangulata accessions were resistant. These results indicated that stripe rust resistance was related to taxonomic origin. Further genetic analysis revealed the resistance of stripe rust in ssp. strangulata accession AS2388 was conferred by a single dominant gene.     

Genetic diversity and gene-pool subdivisions of diploid D-genome <Emphasis Type="Italic">Aegilops tauschii</Emphasis> Coss. (Poaceae) in Iran as revealed by AFLP

The diploid goatgrass Aegilops tauschii is considered the D-genome donor of bread wheat and has probably a centre of diversity in north of Iran. In order to measure the genetic diversity of and the relationships among different populations, varieties and subspecies belonging to Ae. tauschii in Iran, DNA was extracted from 48 accessions of Ae. tauschii collected across the geographic range of the species in the Country and the genetic diversity was assessed using AFLPs based on eight PstI/MseI +3 primer pairs resulted in 277 bands, 198 of which were polymorphic. High level polymorphism was detected, with an average of polymorphism rate of 0.715; relatively low genetic similarity (0.455) between accessions and significant difference between the lowest (0.179) and the highest genetic similarity (0.817). The Iranian Ae. tauschii populations showed high level of genetic diversity. The populations studied were divided into two groups: one group was mainly representing Northern populations collected from Southern Caspian Sea shore and the other group was mainly representing Northeast and Northwest populations. Based on the results of this study, it can be suggested that Ae. tauschii possesses two separate gene-pools in Iran: Northern and Northeastern–Northwestern. Considering the needs for introducing new characteristics and alleles for wheat improvement purposes, Ae. tauschii Iranian gene-pool is assumed to be of high importance for more investigation in the future.     

Allelic diversity of high molecular weight glutenin subunits (HMW-GS) in Iranian Aegilops tauschii Coss. accessions by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE)

Variation of high molecular weight glutenin subunits (HMW-GS) in 28 Iranian Aegilops tauschii (2n = 2x = 14, DD) accessions studied by sodium dodecyl sulphate electrophoresis method (SDS-PAGE). The results showed high variation of HMW-GS in the accessions. The range of frequency in 14 HMW-GS combinations was 3.57–25 % in the accessions. AMOVA showed the molecular variance between the geographic areas was lower than within the geographic areas. According to Nei’s genetic diversity, the highest diversity levels were in Semnan, Golestan and Azarbayjan, on the other hand the lowest levels of diversity were found in Khorasan, Gilan and Mazandaran accessions. Hence, the Caspian Sea South East accessions also Azerbayjan in Iran have more diversity. AMOVA did not show variance between strangulata and tauschii but there was more genetic diversity in ssp. tauschii subspecies in comparison of ssp. strangulata according to Nei’s gene diversity and Shannon information index. It showed Iranian Ae. tauschii have a good potential for bread making quality improvement in bread wheat.     

Polymorphism of <Emphasis Type="Italic">Got2</Emphasis> DNA sequences sheds light on <Emphasis Type="Italic">Aegilops tauschii</Emphasis> Coss. intraspecies divergence and origin of <Emphasis Type="Italic">Triticum aestivum</Emphasis> L.

DNA sequences of nuclear gene Got2 was studied in 60 accessions of Aegilops tauschii, 29 of subsp. tauschii and 31 of subsp. strangulata. It was found that Got2 allozyme polymorphism in Ae. tauschii is due to a single, unique, mutation which led to replacement of glutamic acid by isoleucine in residue 256 of the enzyme molecule, encoded by Got2. As revealed by Got2 DNA sequences variation, initially in its history Ae. tauschii was presented by subsp. strangulata, and among phylogenetic lineages of subsp. strangulata, the lineage “t-9¹s” (TauL3) is the most ancient, a relict one. Subspecies tauschii is relatively “young”. Initially it was presented by the lineage marked by combination of allozyme alleles Got2 ¹⁰⁵ and Acph1 ¹⁰⁰. In the past it inhabited the Continental area from Caucasia to Pakistan, but later on it was forced out by newly originated, now—a major lineage of subsp. tauschii, marked by Got2 ¹⁰⁰. This lineage extended the Continental area of the species up to Kirgizstan, but actually failed to penetrate into pre-Caspian area, occupied by subsp. strangulata. These results essentially differ from those obtained previously, using chloroplast DNA (cpDNA) sequences polymorphism. As revealed by cpDNA, the major, “usual”, subsp. strangulata (TauL2) is “younger” than subsp. tauschii, which resided on phylogenetic tree between relict lineage “t-9¹s”of subsp. strangulata—and major subsp. strangulata. But both cpDNA and Got2 DNA sequences indicate that the level of genetic variation in subsp. tauschii is much lower than in subsp. strangulata. According to Got2 DNA sequences variation, it was Ae. tauschii subsp. strangulata lineage “k-109″ which donated genome D to Triticum aestivum L. This lineage includes accessions: k-109 from South-Eastern Precaspian Azerbaijan; KU-2105, KU-2159 from Western Precaspian Iran; KU-2080 from Eastern Precaspian Iran.     

Genetic diversity of the D-genome in <Emphasis Type="Italic">T. aestivum</Emphasis> and <Emphasis Type="Italic">Aegilops</Emphasis> species using SSR markers

Simple sequence repeats (SSRs), highly dispersed nucleotide sequences in genomes, were used for germplasm analysis and estimation of the genetic relationship of the D-genome among 52 accessions of T. aestivum (AABBDD), Ae. tauschii (D^tD^t), Ae. cylindrica (CCD^cD^c) and Ae. crassa (MMD^cr1D^cr1), collected from 13 different sites in Iran. A set of 21 microsatellite primers, from various locations on the seven D-genome chromosomes, revealed a high level of polymorphism. A total of 273 alleles were detected across all four species and the number of alleles per each microsatellite marker varied from 3 to 27. The highest genetic diversity occurred in Ae. tauschii followed by Ae. crassa, and the genetic distance was the smallest between Ae. tauschii and Ae. cylindrica. Data obtained in this study supports the view that genetic variability in the D-genome of hexaploid wheat is less than in Ae. tauschii. The highest number of unique alleles was observed within Ae. crassa accessions, indicating this species as a great potential source of novel genes for bread wheat improvement. Knowledge of genetic diversity in Aegilops species provides different levels of information which is important in the management of germplasm resources.     

Aegilops tauschii Coss.: allelic variation of enzyme-encoding genes and ecological differentiation of the species

Three hundred and seven accessions of Aegilops tauschii Coss., including 160 of subsp. tauschii and 147 of subsp. strangulata, representing all the species range—from Turkey to Kirgizstan, were analyzed electrophoretically. Twenty polymorphic enzyme-encoding loci were studied, 10 of which were essentially polymorphic in Ae. tauschii. Climatic data for each of the 307 Ae. tauschii habitats were taken from WORLDCLIM database of computer system ArcGIS. Forty-nine climatic parameters were considered: precipitation, minimum, mean and maximum temperatures for each month, and also the total annual level of precipitation. The data were analyzed with multivariate statistical methods, such as Principal Components Analysis (PCA), Multiple Correspondence Analysis (MCA) and Two-Block Partial Least Squares. Variability of climatic conditions among Ae. tauschii habitats is reflected by the two approximately orthogonal “vectors”. The “first vector” is mostly determined by negative impact of precipitation and minimum temperatures during winter. The “second vector” is mostly determined by negative impact of maximum temperatures during summer, and positive impact of precipitation during late spring and summer. Aegilops tauschii is essentially variable along the “second vector”, and especially high level of variation is characteristic for subsp. tauschii. This variation reflects that Ae. tauschii is very tolerable to the climatic variation during summer season. Aegilops tauschii subsp. strangulata is also characterized by the high level of variation along the “first vector”. Moreover, all the habitats of subsp. strangulata fall into the two distinct separate clusters: the habitats in Precaspian Iran, which have the highest minimum temperatures in winter,—and all the other habitats. In the plot of the first two factors of PCA, the “cluster of Precaspian Iran” can be further divided into “Western Precaspian Iran (WPI)”, having relatively higher level of annual rainfall, and relatively dryer “Eastern Precaspian Iran (EPI)”. This three groups of subsp. strangulata accessions, from WPI, EPI and other areas, are also distinctly differed in enzyme-encoding genes allelic variation, as revealed on the plot of the first two axes of MCA. In contrast to subsp. strangulata, the level of variation of subsp. tauschii along the “first vector” is rather low. It was pointed out that variation along “the first vector” reflects adaptive intraspecies divergence of Ae. tauschii: its subspecies strangulata “prefers” the habitats of seaside climate, with warm and moist winter; while subsp. tauschii mostly occupies the habitats with rather continental climate, with relatively cold and dry winter. Allelic variation of enzyme-encoding genes Acph1, Ak, Est2, Est5, Got1, Got2, and Got3 correlate with climate along “the first vector”. Apparently, polymorphism of these loci were involved into the process of Ae. tauschii intraspecies adaptive divergence. Allelic variation of Cat2 and Fdp loci correspond to climatic variation along “the second vector” in subsp. tauschii. Therefore Cat2 and Fdp are likely to be among the genes which polymorphism “helped” subsp. tauschii to succeed in vast geographical expansion far to the east from Caspian Sea.     

Biodiversity of Diploid D-Genome Aegilops Tauschii Coss. in Iran Measured Using Microsatellites

Microsatellite markers were used to analyse the biodiversity of 57 accessions of different subspecies and varieties of wild Aegilops tauschii (2n = 2x = 14; D genome) collected across the major areas where it grows in Iran. Levels of diversity were high, with numbers of alleles averaging 7.3 (ranging up to 12) and polymorphism information contents averaging 0.6591. One accession was notably more similar to two of the D genome in hexaploid wheats (Triticum aestivum) used as outgroups. Within the Ae. tauschii accessions, no markers were characteristic for taxa or geographical origin, suggesting high gene flow between the subspecies and varieties, although some groupings, which could be related to geographical origin, were evident. This survey demonstrates the high diversity present in wild goatgrass in Iran, and indicates that there is value in sampling for useful genes for wheat breeding.     

Polymorphism of gliadins in <Emphasis Type="Italic">Aegilops tauschii</Emphasis> Coss. local populations in two primary habitats in Dagestan

Polymorphism of gliadins was investigated in Aegilops tauschii from primary habitats “4”, near Hily, and “6”, near Rukel, in Dagestan, Russia 205 individual plants were analysed (53/50 and 54/48 plants of subsp. tauschii/subsp. strangulata from the habitats “4” and “6”, respectively) and 1/7 and 18/14 different haplotypes were found among the plants of subsp. tauschii/subsp. strangulata from the habitats “4” and “6”, respectively. No direct evidences of cross-pollination were pointed out, although gliadins electrophoretic phenotypes obtained allowed to suggest that it occur in Ae. tauschii with very low frequency. The data obtained revealed that during Ae. tauschii evolutionary history a local habitat could be populated many times by different phylogenetic lineages of the species. It was found that in Dagestan, at the very edge of the species area, several different lineages belonging to different subspecies could for a long time co-exist together in a local habit, and in such case a very high level of genetic variation in Ae. tauschii could be accumulated on a square of less than one hectare. The further studies of genetic variation in Ae. tauschii local populations, based on molecular genetic methods seems to be very prospective for understanding of peculiarities of the species evolution.     

Geographic patterns of Got1, Got2, Got3 and Est2 enzyme-encoding genes allelic variation in Aegilops tauschii Coss.

Geographic patterns of Got1, Got2, Got3 and Est2 enzyme-encoding genes allelic variation were investigated among 322 accessions of Aegilops tauschii Coss., 161 accessions of ssp. tauschii and 161 accessions of ssp. strangulata, representing all the species area. It was found that: (1) in the two ecologically different subspecies, ssp. tauschii and ssp. strangulata, the patterns of allelic variation of the four genes differ greatly; (2) the same allozymes have originated several times independently in different Ae. tauschii local populations; (3) allelic variation of Got1, Got3 and Est2 in ssp. strangulata corresponds to climatic conditions. The data obtained reflected that Ae. tauschii has been inhabiting its area from ancient times; and allelic variation patterns of Got1, Got2, Got3, Est2 loci were mostly formed by natural selection. Further investigations of these loci with molecular genetic methods are prospective for understanding the peculiarities of Ae. tauschii evolution.     

Aegilops tauschii: Genetic Variation in Iran

All the 79 Aegilops tauschii Coss. accessions of Iranian origin from Prof. Kihara’s collection were analyzed electrophoretically. Of 23 enzyme-encoding loci studied, 11 were polymorphic. In Iran Ae. tauschii is presented by ssp. tauschii and ssp. strangulata which distinctly differ genetically, morphologically and ecologically. Variation patterns of low polymorphic locus Aco2 and highly polymorphic Ep are similar in both subspecies. In contrast, variation of Acph1, Ak, Est2, Est5, Got1, Got2, Got3 and Lap is a set of diverse patterns which markedly differ between subspecies and natural regions also, implying that natural selection is involved.     

Multivariate analysis of genetic variation in Aegilops tauschii from the world germplasm collection

A study of Aegilops tauschii subspecies constitution was undertaken. The data on allozyme and morphologic variation among 308 plants from 154 accessions were used for multivariate analysis. ACPH1 and (glume width)/(rachis segment width) ratio were found to be reliable criteria to distinguish between sspp. tauschii and strangulata.     

Chloroplast DNA non-coding sequences variation in Aegilops tauschii Coss.: evolutionary history of the species

Sequences of four chloroplast DNA non-coding regions, about 3,000?bp in total, were analysed in 112 Aegilops tauschii accessions, 56 of ssp. tauschii and 56 of ssp. strangulata, representing all of the species range. One inversion, 8 insertions/deletions, 18 base pair substitutions and 5 microsatellite loci were found. The data revealed that Ae. tauschii originated in Caucasia. Neither of the two Ae. tauschii subspecies was an ancestor to one another. Aegilops tauschii divided into ssp. tauschii and ssp. strangulata at the very beginning of its existence as a species. Subspecies tauschii was the first to start geographic expansion and relatively rapidly occupied a vast area from Caucasia—eastward up to central Tien Shan and western Himalayas. In contrast to ssp. tauschii, geographic spread of ssp. strangulata was a complicated, multi-stage and slow process. At the beginning of ssp. strangulata evolutionary history its major phylogenetic lineage for a lengthy time span had existed as a small isolated population. Several forms of ssp. strangulata, better adapted to relatively moister and cooler habitats, had originated. Each of these forms has gradually forced out ssp. tauschii from some part of its area in the west, up to central Kopet-Dag.     

Spatial patterns of adenylate kinase,catalase, endopeptidase and fructose-1,6-diphosphatase encoding genes allelic variation in <Emphasis Type="Italic">Aegilops tauschii</Emphasis> Coss.

Investigation of spatial patterns of adenylate kinase, catalase, endopeptidase and fructose-1,6-diphosphatase encoding genes (Ak, Cat1, Cat2, Ep, Fdp) allelic variation in Aegilops tauschii was carried out. About 300 accessions, representing all the species range were taken for the study. Cat2 and Fdp loci are completely monomorphic in ssp. strangulata and in the western part of ssp. tauschii range, as well. Both Cat2 and Fdp are highly polymorphic in the eastern part of ssp. tauschii range, with the patterns of this polymorphism being discordant in these two loci. Ak ¹⁰⁸, a rare allele with sporadical spatial occurrence, was found in ssp. tauschii only. On the contrary, Ak ⁹² is absent in ssp. tauschii: it is the most common Ak allele in ssp. strangulata in Precaspian Iran, the most moist part of the area, and is very rare in other parts of ssp. strangulata area. Ep is a highly polymorphic locus with the highest level of variation in the west of Ae. tauschii area, where this species had originated. Ep allele variation patterns are rather similar in ssp. tauschii and ssp. strangulata. The data reveal the adaptive nature of Ak, Cat2, and Fdp allele variation, while Ep polymorphism seems to be mostly neutral.     

Haplotype variations of gene Ppd-D1 in Aegilops tauschii and their implications on wheat origin

The Ppd-D1 controlling photoperiod response is an important gene for wheat adaptation since it affects heading time. In the present study, three haplotypes, i.e. haplotype I without deletion, haplotype II with a 24?bp deletion, and haplotype III with two deletions of 24 and 15?bp, were identified in the upstream of the coding region in 80 Ae. tauschii accessions. The haplotype distribution was related to subspecies taxon. All typical ssp. tauschii accessions had haplotype I, whereas all ssp. strangulata had haplotype III. The three haplotypes were observed in Ae. tauschii with morphologically intermediate forms between the two typical subspecies. Present results supported that ssp. strangulata or intermediate form was the D-genome donor of common wheat since only haplotype III were found in wheat. Moreover, a 16?bp deletion in exon 8 of gene Ppd-D1 exists in common wheat. However, none of Ae. tauschii accessions analyzed had the 16?bp deletion.     

Simple sequence repeats marker polymorphism in emmer wheat (<Emphasis Type="Italic">Triticum dicoccon</Emphasis> Schrank): Analysis of genetic diversity and differentiation

Genetic diversity was investigated in 73 accessions of emmer wheat (Triticum dicoccon Schrank) from 11 geographical regions using a set of 29 simple-sequence repeat (SSR or microsatellite) markers, representing at least two markers for each chromosome. The SSR primers amplified a total of 357 different alleles with an average of 12.31 alleles per locus. The number of fragments detected by each primer ranged between 6 (Xgwm1066) and 21 (Xgwm268). Null alleles were detected in nine of the 29 primers used. A high level of gene diversity index was observed. Across the 29 primers, gene diversity ranged from 0.60 (Xgwm46) to 0.94 (Xgwm655), with a mean of 0.82. There was a highly significant correlation (r=0.882; p<0.01) between gene diversity index and the number of loci, showing the number of loci per se is a strong indicator of diversity. Analysis of genetic diversity within and among eleven geographical regions revealed most of the genetic diversity of the total sample resided within regions. The coefficient of gene differentiation (Gst = 0.27) showed that the genetic variation within and among the 11 geographical regions was 73 and 27%, respectively. High value of mean number of alleles per locus was found in Iran (4.86) followed by Morocco (4.10) and Armenia (4.03). On the contrary, lower mean number of alleles per locus was detected in Yemen (2.83). The average gene diversity index across regions ranged from 0.52 (Slovakia) to 0.67 (Morocco) with an average of 0.60. Multivariate techniques of principal component analysis and clustering were employed to examine genetic relationship among the 73 emmer wheat accessions vis-à-vis geographical regions of collections. The genetic distance coefficients for all possible 55 pairs of regional comparisons ranged from 0.63 (between Iran and Armenia, Georgia and Azerbaijan, Georgia and Slovakia) to 0.97 (between Morocco and Yemen, Spain and Georgia, and Turkey and Iran) with a mean of 0.82. From the PCA results, a two dimensional plot of PC1 versus PC2 was constructed. The scatter plot of the first two principal components which explained altogether 27% of the total variation depicted the presence of a clear pattern of geographical differentiation except in few cases like accessions from Caucasian region. Similar pattern of genetic relationships among accessions was observed in cluster analysis. The study provided genetic information of emmer wheat in relation to geographical regions of origin. The information could be utilized in crop improvement, germplasm conservation programs, and in further investigation.     

Agro-morphological and molecular variability in <Emphasis Type="Italic">Triticum boeoticum</Emphasis> accessions from Zagros Mountains,Iran

Genetic erosion in cultivated wheat provides a good reason for studying genetic diversity in crop wild relatives. In the present study, genetic diversity of 32 accessions belonging to T. boeoticum species collected from different parts of Iran were evaluated using 13 morphological traits as well as ten inter-simple sequence repeat primers. Statistical analysis for morphological traits showed significant differences among accessions (except number of fertile tillers and total tillers per plant). In principal component analysis, the first three PCA showed 82.65 % of the total morphological variation. Based on the morphological traits, accessions were separated into two main groups by cluster analysis. In molecular analysis, polymerase chain reactions amplified 105 DNA fragments, out of which, 95 (90.47 %) were polymorphic. From geographic perspective, the accessions sampled from western and southwestern of Iran showed the highest and lowest polymorphism, respectively. However, the maximum values of effective number of alleles (Ne), Nei’s gene diversity (He) and Shannon’s information index (I) was related to accessions collected from NW regions. Also, according to cluster analysis and PCoA plot genetic diversity was not related to geographical distribution. Overall, our results revealed a remarkable level of genetic diversity among studied Iranian T. boeoticum accessions; especially accessions collected from Kermanshah and Lorestan provinces, which can be of interest for future breeding programs. So, conservation of germplasm of these areas is recommended.     

Powdery mildew resistance in Aegilops tauschii coss. and synthetic hexaploid wheats

Summary A collection of 400 Ae. tauschii (syn. Ae. squarrosa) Coss. accessions were screened for powdery mildew resistance based on the response patterns of 13 wheat cultivars/lines possessing major resistance genes to nine differential mildew isolates. 106 accessions showed complete resistance to all isolates, and 174 accessions revealed isolate-specific resistance, among which were 40 accessions exhibiting an identical response pattern as wheat cultivar Ulka/^*8Cc which is known to possess resistance gene Pm2. Expression of both complete and isolate-specific resistance from Ae. tauschii was observed in some synthetic hexaploid wheats derived from four mildew susceptible T. durum Desf. parents, each crossed with five to 38 resistant diploid Ae. tauschii accessions. Synthetic amphiploids involving different combinations of T. durum and Ae. tauschii generally showed a decrease in resistance compared with that expressed by the Ae. tauschii parental lines.     

Analysis of genetic diversity in Indian robusta coffee genepool (<Emphasis Type="Italic">Coffea canephora</Emphasis>) in comparison with a representative core collection using SSRs and AFLPs

Genetic diversity among 40 accessions (Coffea canephora) of robusta coffee genepool available in India was determined in comparison with 14 representative samples from a C. canephora core collection and three accessions of C. congensis, using amplified fragment length polymorphism (AFLP) and simple sequence repeats (SSR) markers. Both these molecular approaches were able to generate unique fingerprints for each of the accessions analysed. All the 12 SSR primers used in the present study were found polymorphic, with an average of six alleles per primer pair. Comparative analysis revealed the higher amount of diversity in representatives from a core collection than in the Indian genepool. Moreover, a total of 205 polymorphic AFLP bands were scored in all the 57 accessions analysed. The genetic relationship among 57 accessions was compared on the basis of SSR and AFLP polymorphisms. Genetic similarity dendrograms showed high correlation between the two marker systems. This study clearly established the high amount of diversity present in core samples, which is not represented in Indian genepool. Furthermore, the three accessions of C. congensis did not exhibit any significant diversity from other robusta accessions supporting the school of thought that C. congensis forms a biotype of C. canephora. The potential use of SSRs and AFLP markers in genetic diversity analysis for better ex situ management and also for exploitation of diversity in breeding programmes is discussed.