Combined use of gliadins and SSRs to analyse the genetic variability of the Spanish collection of cultivated diploid wheat (Triticum monococcum L. ssp. monococcum)

This work studied the combined use of gliadins and SSRs to analyse inter- and intra-accession variability of the Spanish collection of cultivated einkorn (Triticum monococcum L. ssp. monococcum) maintained at the CRF-INIA. In general, gliadin loci presented higher discrimination power than SSRs, reflecting the high variability of the gliadins. The loci on chromosome 6A were the most polymorphic with similar PIC values for both marker systems, showing that these markers are very useful for genetic variability studies in wheat. The gliadin results indicated that the Spanish einkorn collection possessed high genetic diversity, being the differentiation large between varieties and small within them. Some associations between gliadin alleles and geographical and agro-morphological data were found. Agro-morphological relations were also observed in the clusters of the SSRs dendrogram. A high concordance was found between gliadins and SSRs for genotype identification. In addition, both systems provide complementary information to resolve the different cases of intra-accession variability not detected at the agro-morphological level, and to identify separately all the genotypes analysed. The combined use of both genetic markers is an excellent tool for genetic resource evaluation in addition to agro-morphological evaluation.     

Gliadins of Bulgarian durum wheat (<Emphasis Type="Italic">Triticum durum</Emphasis> Desf.) landraces: genetic diversity and geographical distribution

The polymorphism of gliadins was studied in 98 Bulgarian durum wheat (Triticum durum Desf.) landraces and classified according to the existing catalogues of blocks of gliadin components. In total, 31 alleles, including 12 new ones, were revealed for five gliadin-coding loci. Nine allele families, which included several alleles coding similar blocks differed only by minor components, were found. The gliadin loci had a high genetic diversity (H = 0.70), and Gli-A2 ^d was the most polymorphic locus. Significant differences in allele distribution were observed through the Bulgarian region under study. The results made it possible to explain the distribution by historical factors. Presumably, the genetic material flew into the country via two different ways and different durum wheat subgroups contributed to the formation of Bulgarian landraces. The landraces were a result of long-term selection and, probably, had a close association with the history of the human populations of the region.     

Genetic Diversity of Glutenin Protein Subunits Composition in Durum Wheat Landraces [Triticum turgidum ssp. turgidum Convar. durum (Desf.) MacKey] from the Mediterranean Basin

The genetic diversity of high and low molecular weight glutenin subunits of 63 durum wheat landraces from different geographical regions in the Mediterranean Basin was studied using SDS-PAGE. Great variability in glutenin composition was found, with 42 high and low molecular weight glutenin haplotypes, 20 allele combinations at the HMW-GS loci, and 18 at the LMW-GS. All five possible LMW models were detected in all Mediterranean regions. Rare alleles were found at Glu-B1 locus in high frequencies and a priori related alleles to grain quality were also observed. Global genetic diversity index was relatively high (0.67); it ranged from 0.33 to 0.66. Cluster analysis on the frequency patterns of origins grouped genotypes following a geographical structure. Rogers’ distance coefficient on frequency pattern for each region of origin showed two germplasm pools with distinct quality profiles, where South West Asian landraces were very different from the landraces of other Mediterranean areas. The relationship between different regions of origin is discussed and two possible ways of introduction of wheat in the Iberian Peninsula (N Africa and SE Europe) are hypothesized. The use of Mediterranean durum wheat landraces as source of genetic variability for grain quality improvement is highly recommended.     

Polymorphism and Genetic Diversity for the Seed Storage Proteins in Spanish Cultivated Einkorn Wheat (Triticum monococcum L. ssp. monococcum)

The seed storage protein composition of one collection of cultivated einkorn wheat (Triticum monococcum L. ssp. monococcum) of Spanish origin has been analysed by SDS-PAGE and A-PAGE. Three allelic variants were detected for the Glu-A1^m, whereas up to six alleles were detected for the Glu-A3^m. For the gliadins, 7 and 14 alleles for the Gli-A1^m and Gli-A2^m were found between the evaluated accessions. Internal variability was detected in some of these materials, which could be related to the landrace nature of them. Up to 48 different genotypes based on the origin and seed storage protein composition have been identified. Further researches on these materials must be carried out for determining the variability degree in morphological traits that could complement the evaluation for their safeguard.     

Temporal variation of diversity in Italian durum wheat germplasm

The aim of this work is to analyse the temporal change of genetic diversity in Italian durum wheat germplasm. The germplasm deployed in this study (158 accessions), belonging to 5 different historical classes, was characterised for its microsatellite and gliadin markers. The level of genetic diversity (He), based on gliadin and SSR markers results – on average – greater in indigenous landraces present in Italy before 1915, with the exception of pure line material which had been selected from landraces (showing highest level of heterozigosity for gliadin markers). Genotypes obtained from crosses or mutagenesis (referring to the 1950–1960 period) along with those resulting from crosses between CIMMYT lines and old materials (1970s and beyond) were also genetically more diverse. Forty-nine percent of indigenous landraces were genetically heterogeneous. Nine out of 53 landrace accessions were able to capture 4 different SSR private alleles. It is speculated that the reduction of allele richness is an indicator of the genetic erosion of the pre-breeding germplasm and it is pointed out that the implementation of appropriate methods of genetic conservation of this germplasm is a priority for breeding and food safety.     

Effects of Prolamins Encoded by Chromosomes 1B and 1D on the Rheological Properties of Dough in Near-Isogenic Lines of Bread Wheat

Fourteen bread wheat near-isogenic lines (NILs) with different alleles at 1B- and 1D-chromosome loci Glu-1, Glu-3 and Gli-1 coding for high molecular weight glutenin subunits (HMW-GS), low molecular weight-GS, and gliadins, respectively, were grown in replicated plots to investigate the individual and combined effects of glutenin and gliadin components on the rheological properties of dough as determined by the Chopin alveograph. NILs did not reveal significant differences in seed yield, protein content, kernel weight, test weight, flour yield, and starch damage. On the contrary, they had a large variation in alveograph dough tenacity P (55–93 mm), swelling G (17–26 mL) and strength W (140–252 J × 10^-4). The null alleles at the Gli-D1/Glu-D3 loci, and allele Glu-D1d (HMW-GS 5+10) were found to have a strong positive influence on dough tenacity and a remarkable negative influence on dough swelling (extensibility) when compared to alleles Gli-D1/Glu-D3b and Glu-D1a (HMW-GS 2+12), respectively. On the other hand, alleles Glu-B1c (HMW-GS 7+9) and Gli-B1/Glu-B3k gave greater G values than alleles Glu-B1u (HMW-GS 7*+8) and Gli-B1/Glu-B3b. The effects of individual Glu-1, Gli-1, or Glu-3 alleles on P and G values were largely additive. The impact of the null allele at Gli-D1/Glu-D3 on gluten strength was highly positive in NILs possessing HMW-GS 2+12, and negligible or negative in NILs containing HMW-GS 5+10, suggesting that there is scope for improving dough quality by utilizing this allele in combination with HMW-GS 2+12. Gli-D1/Glu-D3-encoded prolamins were shown to play a major role in conferring extensibility to dough, and could account for the superior breadmaking characteristics of bread wheat as compared to durum wheat.     

Molecular diversity of Omani wheat revealed by microsatellites: I. Tetraploid landraces

Results of archaeological studies indicate a millennia-old cultivation history for wheat (Triticum spp.) in Oman. However, in spite of numerous collection surveys and efforts for phenotypic characterization of Omani wheat landraces, no attempts have been made using molecular tools to characterize this germplasm. To fill this gap, 29 microsatellite markers revealing 30 loci were used to study the genetic diversity of 38 tetraploid wheat landrace accessions comprising the species T. dicoccon, T. durum and T. aethiopicum. A total of 219 alleles were detected whereby the number of alleles per locus ranged from 2 to 16 with an average number of 7.1 alleles per locus. The highest number of alleles occurred in the B genome with on average 7.9 alleles per locus as compared to the A genome with 6.5 alleles per locus. Heterogeneity was detected for all microsatellites except for GWM 312, GWM 601 and GWM 192B with an average heterogeneity over all primers and lines of 14.4%. Approximately 10% of the accessions contained rare alleles with an average allele frequency <4%. Gene diversity across microsatellite loci ranged from 0.26 to 0.85. The pairwise comparison of genetic similarity ranged from 0.03 to 0.91 with an average of 0.2. Cluster analysis revealed a clear separation of the two species groups T. dicoccon versus T. durum and T. aethiopicum. Within the species clusters regional patterns of subclustering were observed. Overall, this study confirmed the existence of a surprisingly high amount of genetic diversity in Omani wheat landraces as already concluded from previous morphological analyses and showed that SSR markers can be used for landraces’ analysis and a more detailed diversity evaluation.     

Assessment of EST-microsatellites markers for discrimination and genetic diversity in bread and durum wheat landraces from Afghanistan

Accurate and reliable means for identification are necessary to assess the discrimination between landraces of tetraploid wheat [T.␣turgidum L. subsp. durum (Desf.) Husn.] and hexaploid wheat (T. aestivum L. em. Thell.). In Afghanistan, farmers usually cultivate mixed landraces, and thus distinction between bread and durum is difficult. A set of 18 microsatellites derived from the DuPont EST-database were used to describe genetic diversity in a sample of 82 Afghan wheat landraces. A total of 101 alleles were detected, with allele number per locus ranging from 2 to 13, and a mean allele number of 6.31. The percentage of polymorphic loci was 89%. The EST-SSRs markers showed different level of gene diversity: the highest Polymorphism Information Content value (0.921) was observed with DuPw 221. Our results demonstrated that with a reasonable number of expressed sequences target microsatellites (EST-SSRs) it is possible to discriminate between T. durum and T. aestivum species of wheat germplasm. Our results showed that EST-databases could be a useful source for species-specific markers and have the potential for new genic microsatellites markers that could enhance screening germplasm in gene banks.     

Characterisation and Variation of Morphological Traits and Storage Proteins in Spanish Emmer Wheat Germplasm (<Emphasis Type="Italic">Triticum Dicoccon</Emphasis>)

Emmer wheat is hulled wheat that was wide cultivated in Spain at the past. Actually, the most of this germplasm is conserved in Germplasm Banks, and only two small populations have been found in Asturias (North of Spain) in a recent collecting mission. In this work, a collection of 31 Spanish emmer lines developed from identical number of accessions of two Germplasm Banks was analysed for morphological spike traits and seed storage protein composition. Up to seven different botanical varieties were detected, which suggest the presence of a wide diversity, although lower than the historically described 10 botanical varieties. At level of seed storage proteins, the lines showed a high diversity, although the new alleles were present with low frequency in materials with scarce agronomic interest for the farmers (var. atratum, var. lagascae or var. pycnurum). This last circumstance could translate in a lost of variability by genetic drift.     

Polymorphisms in two homeologous γ-gliadin genes and the evolution of cultivated wheat

The polymorphisms in two -gliadin genes GAG56D and GAG56B on the D- and B-genomes of polyploid wheat, respectively, were investigated by sequencing PCR products and by PCR-RFLP. Of GAG56D, two alleles fo and ok were previously known to occur in hexaploid wheat. Here, we found that 16 sequenced fragments of GAG56D from six recognized subspecies of Triticum aestivum, including 13 contributed by this study, were identical to either the fo or the ok allele. Considering published evidence, it was concluded that the investigated alleles of GAG56D stemmed from two different Aegilops tauschii plants and thus two independent origins of hexaploid wheat. Compared to GAG56D-sequences obtained from 10 accessions of Ae. tauschii, the fo and ok alleles clustered with fragments from three accessions collected in the Caspian region. By sequencing fragments of GAG56B, four distinct allelic groups were found among cultivated wheats, typical of bread wheat (p-aes), durum wheat of gliadin 45-type (a), durum wheat of gliadin 42-type (p-dur) and Timopheev's wheat (p-tim), respectively. Interestingly, the a allele found in gliadin 45-type durum wheat was shared by European spelt cultivars, which strongly supported the hypothesis that European spelt originated from a hybridization event between a tetra- and hexaploid wheat. The data also suggested that emmer might have been domesticated more than once. Phylogenetic analysis of GAG56-fragments obtained from putative B/G-genome donors excluded all candidate species as immediate donors of the B/G-genome, but instead indicated a monophyletic origin of all GAG56B alleles found in polyploid wheat, i.e. including T. timopheevii.     

(英文)

对来源于美、中、俄及埃塞阿比亚等22个国家的142份硬粒小麦材料的种子贮藏蛋白位点及遗传变异进行了研究。供试的硬粒小麦(Triticum durum Desf )材料共检测出37条醇溶蛋白条带，无1条带纹为所有材料共有，多态性达到100％，说明硬粒小麦具有丰富的醇溶蛋白等位变异。聚类分析将142份供试材料分为3个大类，材料间遗传差异大小在不同的国家有所不同，表明醇溶蛋白带型与地理来源有一定关系。高分子量谷蛋白电泳共分离出14种亚基和15种亚基组合，但是优质亚基所占比例不高，这可能是因为硬粒小麦加工用途的特殊性，使得多年的育种并未太多改变硬粒小麦高分子量谷蛋白亚基等位变异的频率，促成优质亚基的累计。     

The Inheritance of Morphological and Biochemical Traits Introgressed into Common Wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) from <Emphasis Type="Italic">Aegilops speltoides</Emphasis> Tausch

The genetic control of morphological characters and gliadin composition was studied in two bread wheat lines with introgressed segments from Aegilops speltoides Tausch. It was found that the transferred trait of leaf hairiness is controlled by one dominant gene, non-allelic to the known gene, Hl1. It was localized in 7B chromosome. Whole plant non-glaucousness is under the control of an inhibitor gene, allelic to the gene W1^I of wheat located on chromosome 2B. This gene was found to be epistatic to the gene controlling spike waxlessness. The introgressed gene for spike glume color was found to be allelic to the Rg1 gene located on 1BS of common wheat, but it was linked with another allele of the gliadin locus Gli-B1.     

(英文)

用SDS-PAGE方法测定了我国10个小麦主产省份171份小麦品种和高代品系的高分子量麦谷蛋白亚基（HMW-GS）组成。鉴定出18种HMW-GS，40种HMW-GS组成形式，其中20种亚基其组成形式只在一个品种（系）中出现。Glu-A1位点亚基1和Null出现最多，Glu-B1位点7＋8和7＋9亚基对占绝对优势，Glu-D1位点2＋12亚基对出现频率最高。Null、7＋9、2＋12、Null，7＋8，2＋12，1、7＋8，2＋12，1、7＋9、2＋12等亚基组成形成出现频率最高，占分析品种的49.71％。与前人研究相比，新育成品种HMW-GS亚基组成发生了明显变化，面包优质亚基（对）1、5＋10出现的频率显著升高，亚基多态性增加，组成形式明显改善，这些对于品质改良和品种选育是非常有利的，新育成品种Glu-1品质评分已超过7。尽管个别品种亚基组成好，品质优良，但总体上看，我国小麦品种与其它国家相比品质还存在一定差距，提高5＋10、17＋18等优质亚基的频率是改善我国小麦面包品质的重要措施。     

Allelic diversity of HMW and LMW glutenin subunits and omega-gliadins in French bread wheat (Triticum aestivum L.)

Wheat endosperm storage proteins, namely gliadins and glutenins, are the major components of gluten. They play an important role in dough properties and in bread making quality in various wheat varieties. In the present study, the different alleles encoded at the 6 glutenin loci and at 3 -gliadin loci were identified from a set of 200 hexaploid wheat cultivars grown primarily in France using SDS PAGE. At Glu-A1, Glu-B1 and Glu-D1, encoding high molecular weight glutenin subunits (HMW-GS), 3, 8 and 5 alleles were observed respectively. Low molecular weight glutenin subunits (LMW-GS) displayed similar polymorphism, as 5 and 11 alleles were identified at loci Glu-A3 and Glu-B3 respectively. Four alleles were observed at Glu-D3 loci. Omega-gliadin diversity was also very high, as 7, 13 and 9 alleles were found at Gli-A1, Gli-B1 and Gli-D1, respectively. A total of 147 (or 149) patterns resulted from the genetic combination of the alleles encoding at the six glutenin loci (or Glu-1 and Gli-1 loci). Although Glu-1 and Glu-3 loci were located on different chromosome arms and were theoretically independent, some associations were revealed due to pedigree relatedness between some French wheat cultivars. The usefulness of allelic identification of LMW-GS together with HMW-GS and gliadins for future genetic and technological wheat improvement is discussed.     

Dispersal of durum wheat [<Emphasis Type="Italic">Triticum turgidum</Emphasis> L. ssp. <Emphasis Type="Italic">turgidum</Emphasis> convar. <Emphasis Type="Italic">durum</Emphasis> (Desf.) MacKey] landraces across the Mediterranean basin assessed by AFLPs and microsatellites

A comprehensive characterization of crop germplasm is critical to the optimal improvement of the quality and productivity of crops. Genetic relationships and variability were evaluated among 63 durum wheat landraces from the Mediterranean basin using amplified fragment length polymorphisms (AFLPs) and microsatellites markers. The genetic diversity indices found were comparable to those of other crop species, with average polymorphism information content (PIC) values of 0.24 and 0.70 for AFLP and microsatellites, respectively. The mean number of alleles observed for the microsatellites loci was 9.15. Non-metric multi-dimensional scaling clustered the accessions according to their geographical origin with the landraces from the South shore of the Mediterranean Sea closely related. The results support two dispersal patterns of durum wheat in the Mediterranean basin, one through its north side and a second one through its south side.     

Evaluation of genetic diversity and relationships within an on-farm collection of Perilla frutescens (L.) Britt. using microsatellite markers

The present study demonstrates utilization of 11 microsatellite markers to explore genetic diversity held in Perilla frutescens (L.) Britt. landrace accessions growing on farms in different parts of Korea and Japan and to assess their genetic relationships. All microsatellite loci were polymorphic and produced a total of 96 alleles ranging from 4 to 20, with an average of 8.7 alleles per locus. Of the 96 alleles found, a total of 15 unique landrace-specific alleles were observed at 9 different loci. The locus GBPFM203 provided the highest number of alleles (20), of which five were unique and each specific to a particular landrace accession. The occurrence of unique, accession-specific alleles presented molecular evidence for the generation of new alleles within on-farm collection of Perilla. The mean values of observed (H _O) and expected heterozygosity (H _E) were 0.39 and 0.68, respectively, indicating a considerable amount of polymorphism within this collection. A genetic distance-based phylogeny grouped the two Perilla varieties, var. frutescens and var. crispa (Thunb.) Decne into two distinct groups. Accessions belonging to var. frutescens could also be divided into two subgroups at a close genetic distance (GD = 0.432). The overall clustering pattern did not strictly follow the grouping of accessions according to their geographic origins. These observations are indicative of extensive germplasm exchange among farms from different geographical regions. The genetic similarity observed among the Perilla landraces may be useful for future Perilla crop variety identification, conservation, and improvement programs.     

Isoenzymatic variability in an apple germplasm bank

Apple (Malus domestica Borkh.) is a species, which has a very high degree of morphologic and genetic variability. Genetic variability within a group formed by 277 old varieties from Navarra has been studied through isoenzymatic analysis. 14 loci, corresponding to 7 isoenzymatic systems, were visualized, detecting between 1 and 5 alleles per locus. The combinations of all 12 polymorphic isoenzymes allowed the identification of 263 isoenzymatic groups, 251 of which include a single accession. Average similarity for the different accessions in the bank was J = 0.58 and cophenetic correlation between the similarity matrix and dendrogram was good (r = 0.80). Thus, the groups obtained reflect taxonomic relationships between accessions correctly.     

Assessment of genetic diversity in emmer (Triticum dicoccon Schrank) × durum wheat (Triticum durum Desf.) derived lines and their parents using mapped and unmapped molecular markers

In the last few years, the renewed interest for emmer wheat (Triticum dicoccon Schrank) in Italy has stimulated breeding programs for this crop releasing improved genotypes obtained not only by selection from landraces, but even by crosses with durum wheat (Triticum durum Desf.) varieties. The purpose of this work has been to uncover the genetic make-up of some emmer × durum derivatives, specifically by comparing the differences from their parents. Genetic diversity of advanced breeding lines and varieties derived from a durum × emmer cross has been evaluated on the basis of AFLP and SSR markers in comparison with the corresponding emmer and durum wheat parent for addressing the seminal question of how much ‘wild’ variation remains after selection for agronomic type.     

Studying the extent of genetic diversity among Gossypium arboreum L. genotypes/cultivars using DNA fingerprinting

Genetic diversity is an area of concern for sustaining crop yield. Information on genetic relatedness/diversity among Gossypium arboreum L. cultivars/genotypes is scanty. We have used random amplified polymorphic DNA (RAPD) analysis to assess the genetic divergence/relationship among 30 genotypes/cultivars of G. arboreum. Of 45 primers surveyed, 63% were polymorphic. Out of the total number of loci amplified, 36% were polymorphic. The calculated genetic similarity between the cultivars/genotypes was in the range of 47.05–98.73%. Two genotypes, HK-244 and Entry-17, were the most distantly related. The average genetic relatedness among all the genotypes was 80.46%. However, most of the cultivated varieties showed a close genetic relationship, indicating a narrow genetic base in comparison to the non-cultivated germplasm. The calculated coefficients were used to construct a dendrogram using the unweighted pair group of arithmetic means (UPGMA) algorithm, which grouped the genotypes/cultivars into two major and three smaller clusters. The study is the first comprehensive analysis of the genetic diversity of G. arboreum germplasm and identifies cultivars that will be useful in extending the genetic diversity of cultivated varieties and future genome mapping projects.     

Haplotype analysis of molecular markers linked to stem rust resistance genes in Ethiopian improved durum wheat varieties and tetraploid wheat landraces

The recent emergence of wheat stem rust race Ug99 (TTKSK) and related strains threaten Ethiopian as well as world wheat production because they overcome widely used resistance genes that had been effective for many years. The major cause which aggravates the ineffectiveness of Ethiopian wheat varieties against stem rust is the narrow genetic base on which the breeding for resistance has been founded, however, little is known about the resistance genotypes of Ethiopian durum wheat varieties and tetraploid wheat landraces. The objective of the study was to identify stem rust resistance genes that are present in the Ethiopian tetraploid wheat landraces and improved durum wheat varieties using molecular markers and assess which genes are effective for current Ethiopian stem rust races of Puccinia graminis f. sp. tritici including Ug99. The investigated 58 tetraploid wheat accessions consisted of 32 (Triticum durum s.l. incl. Triticum aethiopicum Jakubz., Triticum polonicum) landraces and 22 registered T. durum varieties released in Ethiopia between 1966 and 2009 and four T. durum varieties from ICARDA. A total of 17 molecular markers (SSR, EST and InDel) linked or diagnostic for stem rust resistance genes Sr2, Sr13, Sr22 and Sr35 were used for genotyping. Haplotype analysis indicated that only few of the Ethiopian durum wheat varieties carried Sr13. The resistant variety ‘Sebatel’ showed a haplotype for Sr2 and Sr22 and variety ‘Boohai’ for Sr22, however further evaluation is needed for the diagnostic value of these haplotypes. This study is the first report on the presence of stem rust resistance (Sr) genes in Ethiopian durum wheat varieties and tetraploid wheat landraces based on linked or associated molecular markers. Thus it might help in the identification of varieties carrying resistant alleles that provide valuable genetic material for the development of new improved varieties in further breeding programmes.