Electrophoretic analysis of the high-molecular-weight glutenin subunits of Triticum monococcum,T. urartu,and the A genome of bread wheat (T. aestivum)

Summary The high molecular weight (HMW) subunit composition of glutenin was analysed by sodium dodecyl sulphate, polyacrylamide gel electrophoresis (SDS-PAGE) in the A genome of 497 diploid wheats and in 851 landraces of bread wheat. The material comprised 209 accessions of wild Triticum monococcum ssp. boeoticum from Greece, Turkey, Lebanon, Armenia, Iraq, and Iran; 132 accessions of the primitive domesticate T. monococcum ssp. monococcum from many different germplasm collections; one accession of free-threshing T. monococcum ssp. sinskajae; 155 accessions of wild T. urartu from Lebanon, Turkey, Armenia, Iraq, and Iran; and landraces of T. aestivum, mainly from the Mediterranean area and countries bordering on the Himalayan Mountains. Four novel HMW glutenin sub-units were discovered in the landraces of bread wheat, and the alleles that control them were designated Glu-Ald through Glu-Alg, respectively. The HMW subunits of T. monococcum ssp. boeoticum have a major, x subunit of slow mobility and several, less prominent, y subunits of greater mobility, all of which fall within the mobility range of HMW subunits reported for bread wheat. In T. monococcum ssp. monococcum the range of the banding patterns for HMW subunits was similar to that of ssp. boeoticum. However, two accessions, while containing y subunits were null for x subunits. The single accession of Triticum monococcum ssp. sinskajae had a banding pattern similar to that of most ssp. boeoticum and ssp. monococcum accessions. The HMW subunit banding patterns of T. urartu accessions were distinct from those of T. monococcum. All of them contained one major x and most contained one major y subunit. In the other accessions a y subunit was not expressed. The active genes for y subunits, if transferred to bread wheat, may be useful in improving bread-making quality.     

High molecular weight glutenin subunit variation in wild and cultivated einkorn wheats (Triticum spp.,Poaceae)

Variation in high molecular weight (HMW) glutenin subunit composition among wild and cultivated einkorn wheats (2n = 2x = 14, AA) was investigated using one- (SDS-PAGE and urea/SDS-PAGE) and two-dimensional (IEF × SDS-PAGE) electrophoretic analyses. The material comprised 150 accessions ofTriticum urartu, 160 accessions ofT. boeoticum, 24 accessions ofT. boeoticum subsp.thaoudar and 74 accessions of primitive domesticatedT. monococcum from many different germplasm collections. The biochemical characteristics of HMW-glutenin subunits ofT. boeoticum andT. monococcum were highly similar to one another but distinctly different from those ofT. urartu. All the species analysed were characterised by large intraspecific variation and only three HMW-glutenin subunit patterns were identical betweenT. boeoticum andT. monococcum. Consistent with the distinct nature ofT. urartu, all its HMW-glutenin patterns were different from those found inT. boeoticum andT. monococcum. The differences detected between these species might reflect their reproductive isolation and are consistent with recent nomenclatural and biosystematic treatments that recogniseT. urartu as separate species fromT. boeoticum andT. monococcum. The presence of three distinct glutenin components in some accessions of the species studied seems to be evidence for the existence of at least three active genes controlling the synthesis of the HMW-glutenin subunits in the A genome of wild and primitive domesticated diploid wheats. Results indicate also that HMW-glutenin subunits could represent useful markers for the evaluation of genetic variability present in different wild diploid wheat collections and subsequently for their conservation and future utilisation.     

Species relationships and genetic variation in the diploid wheats (Triticum,Aegilops) as revealed by starch gel electrophoresis

Twenty enzyme loci were examined in the diploid species ofTriticum andAegilops for allelic variation by starch gel electrophoresis. SectionSitopsis, including the five species,Ae. speltoides, Ae. lingissima, Ae. sharonensis, Ae. bicornis andAe. searsii form a close subgroup withAe. speltoides slightly removed from the others.T. monococcum s. lat., was found to be closest to the species of theSitopsis group.Ae. comosa, Ae. umbellulata andAe. uniaristata form a second subgroup withAe. caudata most closely related to these species.Ae. squarrosa appears almost equally related to all of the species, showing no special affinity for any one species group. Nineteen out of twenty loci examined were polymorphic with a mean of 6.7 alleles per locus. Species could be, for most loci, characterized by the presence of predominant alleles. A conspicious genetic characteristic ofTriticum-Aegilops is the sharing of these predominant alleles between species. Within species variation is characterized by a diffuse distribution of secondary alleles.     

Genetic variability of the wild diploid wheat Triticum urartu revealed by RFLP and RAPD markers

 Genetic variability among 49 accessions of Triticum urartu was estimated by RFLP and RAPD marker analyses, and the two data sets were compared. One T. timopheevii accession and two accessions of T. durum and T. aestivum, respectively, were included to identify T. urartu accessions closely related to these polyploid wheats. Twenty eight RFLP clones and 29 RAPD primers generated 451 and 155 polymorphic bands, respectively. The three accessions from Armenia clustered together and were well separated from all other accessions, which showed less pronounced geographical patterns. Genetic similarity and co-phenetic values calculated with RAPD markers were very similar to those calculated with RFLP markers for the intraspecific comparisons, but not for the interspecific comparisons. The identification of individual T. urartu accessions which are more related to polyploid wheats than others was not possible. Received: 14 May 1996 / Accepted: 13 September 1996     

Isozyme variation in some populations of wild diploid wheats in Iran

Isozyme electrophoresis data of seed extracts from 11 populations of diploid wheat species (Triticum boeoticum Bioss. and Triticum urartu Thumanian ex Gandilyan), distributed mainly in the western and west-northern Iran, were investigated. The five enzyme systems used were peroxidase, polyphenol oxidase, superoxide dismutase, malate dehydrogenase and catalase. The first three were found to be useful as molecular marker for characterization of diploid wheat populations. A total of 13 bands from three enzyme systems were recorded. The value of a ‘Jaccard's’ similarity coefficient ranges from 0.333 to 1.000. Data analysis was done using clustering method UPGMA. On the basis of Jaccard's coefficient, the obtained dendrogram supports previous relationship between T. boeoticum and T. urartu as separate species as well as reflecting their distinct gene pools and substantiating their specific recognition despite the overall morphological similarity.     

Parental genome expression in synthetic wheats (Triticum turgidum sp. × T. tauschii sp.) revealed by two-dimensional electrophoresis of seedling proteins

Summary Two-dimensional gel electrophoresis was conducted on etiolated seedling proteins from two distinct amphiploids (ABD1, ABD2) and their parental lines (AB1, D1 and AB2, D2), AB1 and AB2 being used as female. On the amphiploid patterns were found all the parental spots except 8 D spots of which 3 are cytoplasmically encoded. One exceptional polypeptide observed in ABD1 was present neither in AB1 nor D1. The patterns fromt the amphiploids very closely resemble the co-electrophoresis done with 1/3 D protein extract and 2/3 AB protein extract. Thus it is very likely that for most gene products revealed the genomes act independently of each other.     

Wx gene in diploid wheat: molecular characterization of five novel alleles from einkorn (Triticum monococcum L. ssp. monococcum) and T. urartu

The Wx gene encodes the granule-bound starch synthase I or waxy protein, which is the sole enzyme responsible for amylose synthesis in wheat seeds. Triticum urartu and einkorn (T. monococcum L. ssp. monococcum), which are related to the A genome of bread wheat, could be important sources of variation for this gene. This study evaluated the Wx gene variability in 52 accessions of these species and compared their nucleotide sequences with the Wx-A1a allele of bread wheat. The level of polymorphism found was high, although not distributed equally between the two species. Five different alleles were found in T. urartu, of which four were novel (Wx-A ^u 1b, -A ^u 1c, -A ^u 1d and -A ^u 1e). All einkorn accessions had the same allele, which was also novel and was named Wx-A ^m 1a. A comparison between the proteins deduced from the novel alleles and the Wx-A1a protein showed that there were up to 33 amino acid changes in both the transit peptide and the mature protein. These results showed that these species, especially T. urartu, are a potential source of novel waxy variants.     

NADP-dependent aromatic alcohol dehydrogenase in polyploid wheats and their diploid relatives. On the origin and phylogeny of polyploid wheats

Summary The three major isoenzymes of the NADP-dependent aromatic alcohol dehydrogenase (ADH-B), distinguished in polyploid wheats by means of polyacrylamide gel electrophoresis, are shown to be coded by homoeoalleles of the locus Adh-2 on short arms of chromosomes of the fifth homoeologous group. Essentially codominant expression of the Adh-2 homoeolleles of composite genomes was observed in young seedlings of hexaploid wheats (T. aestivum s.l.) and tetraploid wheats of the emmer group (T. turgidum s.l.), whereas only the isoenzyme characteristic of the A genome is present in the seedlings of the timopheevii-group tetraploids (T. timopheevii s.str. and T. araraticum).The slowest-moving B³ isoenzyme of polyploid wheats, coded by the homoeoallele of the B genome, is characteristic of the diploid species Aegilops speltoides S.l., including both its awned and awnless forms, but was not encountered in Ae. bicornis, Ae. sharonensis and Ae. longissima. The last two diploids, as well as Ae. tauschii, Ae. caudata, Triticum monococcum s.str., T. boeoticum s.l. (incl. T. thaoudar) and T. urartu all shared a common isoenzyme coinciding electrophoretically with the band B² controlled by the A and D genome homoeoalleles in polyploid wheats. Ae. bicomis is characterized by the slowest isoenzyme, B⁴, not found in wheats and in the other diploid Aegilops species studied.Two electrophoretic variants of ADH-B, B¹ and B², considered to be alloenzymes of the A genome homoeoallele, were observed in T. dicoccoides, T. dicoccon, T. turgidum. s.str. and T. spelta, whereas B² was characteristic of T. timopheevii s.l. and only B¹ was found in the remaining taxa of polyploid wheats. The isoenzyme B¹, not encountered among diploid species, is considered to be a mutational derivative which arose on the tetraploid level from its more ancestral form B² characteristic of diploid wheats.The implication of the ADH-B isoenzyme data to the problems of wheat phylogeny and gene evolution is discussed.     

Genetic diversity and phenotypic variation in marginal populations of the locally endangered speciesHordeum secalinum (Poaceae)

Electrophoresis was used to compare variation in hordein polypeptide patterns and isozymes in five marginal populations ofHordeum secalinum (four Swedish and one Danish population) and four populations along the Atlantic coast from Denmark to Spain. Hordein patterns were uniform within and among Swedish and Danish populations whereas the materials from France and Spain were divergent. The banding patterns for nine isozymes (AAT, IDH, MDH, PGD, GPI, ME, ACP, EST, and PRX) agreed with those reported for otherHordeum species. All putative loci were monomorphic with the exception of PRX, which showed three different phenotypes. The five marginal populations varied in seed set and cultivated plants differed in phenological traits.Dedicated to emer. Univ.-Prof. DrFriedrich Ehrendorfer on the occasion of his 70th birthday     

NAD-dependent aromatic alcohol dehydrogenase in wheats (Triticum L.) and goatgrasses (Aegilops L.): evolutionary genetics

Summary Evolutionary electrophoretic variation of a NAD-specific aromatic alcohol dehydrogenase, AADH-E, in wheat and goatgrass species is described and discussed in comparison with a NAD-specific alcohol dehydrogenase (ADH-A) and a NADP-dependent AADH-B studied previously. Cultivated tetraploid emmer wheats (T. turgidum s. l.) and hexaploid bread wheats (T. aestivum s. l.) are all fixed for a heterozygous triplet, E^0.58/E^0.64. The slowest isoenzyme, E^0.58, is controlled by a homoeoallelic gene on the chromosome arm 6AL of T. aestivum cv. Chinese Spring and is inherent in all diploid wheats, T. monococcum s. Str., T. boeoticum s. l. and T. urartu. The fastest isoenzyme, E^0.64, is presumably controlled by the B- and D-genome homoeoalleles of the bread wheat and is the commonest alloenzyme of diploid goat-grasses, including Ae. speltaides and Ae. tauschii. The tetraploid T. timopheevii s. str. has a particular heterozygous triplet E^0.56/E^0.71, whereas the hexaploid T. zhukovskyi exhibited polymorphism with electromorphs characteristic of T. timopheevii and T. monococcum. Wild tetraploid wheats, T. dicoccoides and T. araraticum, showed partially homologous intraspecific variation of AADH-E with heterozygous triplets E^0.58/E^0.64 (the commonest), E^0.58/E^0.71, E^0.45/E^0.58, E^0.48/E^0.58 and E^0.56/E^0.58 recorded. Polyploid goatgrasses of the D-genome group, excepting Ae. cylindrica, are fixed for the common triplet E^0.58/E^0.64. Ae. cylindrica and polyploid goatgrasses of the C^u-genome group, excepting Ae. kotschyi, are homozygous for E^0.64. Ae. kotschyi is exceptional, showing fixed heterozygosity for both AADH-E and ADH-A with unique triplets E^0.56/E^0.64 and A^0.49/A^0.56.     

Genetic diversity in wild wheats and goat grass

The genetic structure of 35 populations of wild relatives of cultivated wheats, all collected in Syria and Lebanon, was assessed using ten isozymes. The populations consisted of diploid goat grass, Aegilops speltoides, diploid wild wheats, Triticum monococcum spp. aegilopoides and T. urartu, and tetraploid wild wheat, T. turgidum ssp. dicoccoides. The majority of the populations were polymorphic (P=0–70%) having low within-population mean genetic diversity (H_ep=0.05–0.10) and relatively high within-species genetic diversity (H_es=0.14–0.31). The linkage between loci did not seem to be one of the causes for the observed polymorphism. All four species showed significant inbreeding at both the population (0.31–0.64) and species (0.77–0.96) levels, and the extent of inbreeding did not correlate with mating systems. Despite their apparent common ecological and evolutionary history, between-population or between-species level genetic identity was low (I=0.43–0.86). Among the diploid species, populations of Ae. speltoides clustered distinctly from those overlapping clusters of T. monococcum ssp. aegilopoides and T. urartu. The tetraploid species T. turgidum ssp. dicoccoides had relatively less genetic diversity (H_es=0.14) and was highly homozygous (F=0.96). The results suggest that these wild progenitors of cultivated wheats have undergone extensive local differentiation and inbreeding. We discuss the implications of our results on the management of wild wheat and goat grass populations. Received: 12 September 1999 / Accepted: 10 November 1999     

Genetic diversity and environmental associations of wild barley,Hordeum spontaneum (Poaceae), in Iran

Genetic diversity and structure of populations of the wild progenitor of barleyHordeum spontaneum in Iran was studied by electrophoretically discernible allozymic variation in proteins encoded by 30 gene loci in 509 individuals representing 13 populations of wild barley. The results indicate that: a)Hordeum spontaneum in Iran is extremely rich genetically but, because of predominant self-pollination, the variation is carried primarily by different homozygotes in the population. Thus, genetic indices of polymorphismP-1% = 0.375, range = 0.267–0.500, and of genetic diversity,He = 0.134, range = 0.069–0.198, are very high. b) Genetic differentiation of populations includes clinal, regional and local patterns, sometimes displaying sharp geographic differentiation over short distances. The average relative differentiation among populations isGst = 0.28, range = 0.02–0.61. c) A substantial portion of the patterns of allozyme variation in the wild gene pool is significanctly correlated with the environment and is predictable ecologically, chiefly by combinations of temperature and humidity variables. d) The natural populations studied, on the average, are more variable than two composite crosses, and more variable than indigenous land races of cultivated barely,Hordeum vulgare, in Iran. — The spatial patterns and environmental correlates and predictors of genetic variation ofH. spontaneum in Iran indicate that genetic variation in wild barley populations is not only rich but also at least partly adaptive. Therefore, a much fuller exploitation of these genetic resources by breeding for disease resistance and economically important agronomic traits is warranted.     

Heterochromatin differentiation and phylogenetic relationship of the A genomes in diploid and polyploid wheats

Summary Heterochromatin differentiation, including band size, sites, and Giemsa staining intensity, was analyzed by the HKG (HCl-KOH-Giemsa) banding technique in the A genomes of 21 diploid (Triticum urartu, T. boeoticum and T. monococcum), 13 tetraploid (T. araraticum, T. timopheevi, T. dicoccoides and T. turgidum var. Dicoccon, Polonicum), and 7 cultivars of hexaploid (T. aestivum) wheats from different germplasm collections. Among wild and cultivated diploid taxa, heterochromatin was located mainly at centromeric regions, but the size and staining intensity were distinct and some accessions' genomes had interstitial and telomeric bands. Among wild and cultivated polyploid wheats, heterochromatin exhibited bifurcated differentiation. Heterochromatinization occurred in chromosomes 4A^t and 7A^t and in smaller amounts in 2A^t, 3A^t, 5A^t, and 6A^t within the genomes of the tetraploid Timopheevi group (T. araraticum, and T. timopheevi) and vice versa within those of the Emmer group (T. dicoccoides and T. turgidum). Similar divergence patterns occurred among chromosome 4A^a and 7A^a of cultivars of hexaploid wheat (T. aestivum). These dynamic processes could be related to geographic distribution and to natural and artifical selection. Comparison of the A genomes of diploid wheats with those of polyploid wheats shows that the A genomes in existing diploid wheats could not be the direct donors of those in polyploid wheats, but that the extant taxa of diploids and polyploids probably have a common origin and share a common A-genomelike ancestor.Contribution of the College of Agricultural Sciences, Texas Tech Univ. Journal No. T-4-233.     

Esterase isozyme variation in theEragrostis curvula complex (Poaceae)

The biosystematic relationships of the apomictic complexEragrostis curvula s. lato, is investigated by disc electrophoresis of seed extracts to obtain esterase patterns of 23 accessions representing the morphological variants of this complex: curvula, conferta, robusta, chloromelas and lehmanniana. The zymograms thus obtained were classified into four groups on the basis of the presence of certain bands taken as characteristic and constant markers. Within each group variations were found in strict accordance with the morphological and cytogenetic data available on the complex. Cluster analysis showed similarity levels between the strains studied, representing different genomic groups. The esterase pattern proved useful as an additional criterion for identifying the individual taxa making up the complex and for evaluating their reciprocal relationships.     

Isozyme evidence on the genetic diversity, mating system and evolution of Bromus intermedius (Poaceae)

Genetic diversity and differentiation among the B. intermedius accessions of different geographic origin has been studied using isozyme analysis. The mating system was evaluated on the basis of allozyme polymorphism. Outcrossing rate (t) in B. intermedius was mostly 0, except one population with t = 0.16, indicating nearly complete autogamy in this species. Given that B. arvensis and B. intermedius had common allozymes of all isozymes studied, it is suggested that B. intermedius may be a direct autogamous derivative of the outcrosser B. arvensis. Contrary to expectations, the allozyme diversity in B. intermedius was higher than in B. arvensis, 23 and 16 allozymes, respectively. Geographic pattern was found among the accessions of B. intermedius.     

RFLP markers associated with Sr22 and recombination between chromosome 7A of bread wheat and the diploid species Triticum boeoticum

Analysis of the bread wheat variety Schomburgk, and related lines in its pedigree, identified RFLP markers associated with the segment of chromosome 7A carrying the Sr22 gene derived from the diploid species T. boeoticum. The distribution of the RFLP markers indicated that at least 50% of 7AS and 80% of 7AL in Schomburgk is of T. boeoticum origin. Evaluation of five sets of nearisogenic lines, backcross lines in 20 different genetic backgrounds and an F₂ population segregating for Sr22 demonstrated a very low level of recombination between the 7A chromosomes of T. boeoticum and T. aestivum. Several recombinants carrying Sr22 but with a much reduced segment of T. boeoticum were identified and these may prove useful in the breeding of further varieties with Sr22.     

The presence of the enhanced K/Na discrimination trait in diploid Triticum species

Summary A number of accessions of the three species of diploid wheat, Triticum boeoticum, T. monococcum, and T. urartu, were grown in 50 mol m^-3 NaCl+2.5 mol m^-3 CaCl₂. Sodium accumulation in the leaves was low and potassium concentrations remained high. This was not the case in T. durum grown under the same conditions, and indicates the presence in diploid wheats of the enhanced K/Na discrimination character which has previously been found in Aegilops squarrosa and hexaploid wheat. None of the accessions of diploid wheat showed poor K/Na discrimination, which suggests that if the A genome of modern tetraploid wheats was derived from a diploid Triticum species, then the enhanced K/Na discrimination character became altered after the formation of the original allopolyploid. Another possibility is that a diploid wheat that did not have the enhanced K/Na discrimination character was involved in the hybridization event which produced tetraploid wheat, and that this diploid is now extinct or has not yet been discovered.     

Giemsa C-banded karyotypes of diploid and tetraploidHordeum bulbosum (Poaceae)

The similar-looking basic genomes ofHordeum bulbosum (2x and 4x) have five rather similar metacentric, one submetacentric, and one satellited choromosome. C-banding patterns are characterized by one or two centromeric, or juxtacentromeric, small to larger bands in most chromosomes, by bands at the nucleolar organizers, by small or very small telomeric bands, and by the nearly complete lack of intercalary bands. Banding pattern polymorphism is widespread. Banding patterns supported by chromosome morphology enable identification of homologues, and discrimination between non-homologues inH. bulbosum (2x). The C-banded karyotype ofH. bulbosum (4x) supports an autopolyploid origin, but it was possible to identify only homologues of submetacentrics and SAT-chromosomes.     

Sieve-element plastids ofTriticum andAegilops (Poaceae)

Fourteen taxa of the Triticum-Aegilops group have been investigated for their sieve-element plastids. At maturity they contain dense and thin crystalloid inclusions and are classified into the PIIc' plastid type; onlyAe. comosa var.biaristata lacked the thin crystalloids and thus conforms to the PII c type. The proteinaceous nature of the crystalloids was demonstrated by application of proteolytic enzymes. Ultrastructural evidence suggests that both kinds of crystalloid inclusions are involved in the sealing of sieve-plate pores of injured sieve tubes. Measurements and calculations of the spacings and angles carried out on crystalloid prints permitted the construction of a two- and three-dimensional pattern forT. aestivum thin crystalloids.