Tetraploid Wheat Germplasm Research Articles

Genetic and Morpho-Agronomic Characterization of Sicilian Tetraploid Wheat Germplasm.

Cereal landraces are a very valuable resource in contemporary agriculture. A renewed focus for breeding purposes could ameliorate some negative consequences of modern agriculture and conventional breeding, such as the loss of genetic diversity. One strategy combining molecular genotyping and characterization of morpho-agronomic traits related to productivity is proposed to assess a group of tetraploid wheat landraces named Bufala, historically cultivated in the mountain areas of Sicily and characterized by adaptability in terms of cold tolerance, ability to grow in marginal soils, weed competitiveness and resistance to diseases. A total of 55 SSR molecular markers were used to detect patterns of diversity in 30 rivet and durum wheat genotypes. Furthermore, phenotyping was then conducted for 8 morpho-agronomic traits. Discriminant analysis of principal components (DAPC), STRUCTURE and phylogenetical analysis allowed to identify three groups, two of them genetically close and including both Bufala and Bufala-related rivet landraces. To the third group, old and more recent durum wheat varieties, constituting the outgroup, were assigned. Clustering was confirmed by Principal Component Analysis (PCA). Finally, a correlation analysis showed that Bufala genotypes are characterized by lower ear density, major ear length and later earing time compared with the other studied genotypes. The levels of diversity and population structure could be an important contribution to parent selection in tetraploid wheat breeding programs, as well as to germplasm conservation and management.

The Genetic Potential of a Germplasm of Interspecific Crosses between Durum Wheats (Triticum turgidumL. ssp.durum(Desf.) Husn.) and their Relatives (T. dicoccumSchübl. andT. polonicumL.) in Five Glutenin Loci

Wheat endosperm storage proteins 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 5 glutenin loci were identified from a set of 38 tetraploid wheat germplasm obtained from interspecific crosses between durum wheats (Triticum turgidum L. ssp. durum (Desf.) Husn.) and their relatives (T. dicoccum Schubl. and T. polonicum L.) using SDS-PAGE. At Glu-A1 and Glu-B1, encoding high molecular weight glutenin subunits (HMW-GS), 2 and 4 alleles were observed, respectively. Low molecular weight glutenin subunits (LMW-GS) displayed similar polymorphism, as 3, 5 and 3 alleles were identified at loci Glu-A3, Glu-B3 and Glu-B2, respectively. One new allele was detected at Glu-B3 locus and appeared in nine accessions obtained from five crosses. This allele codes for five subunits (2 + 8 + 9 + 13 + 18), encoded by the Glu-B3b without subunit 16 plus subunits 2 and 18. A total of 38 patterns resulted from the genetic combination of the alleles encoding at the five glutenin loci. This led to a significantly higher Nei coefficient of genetic variation in Glu-1, Glu-3 and Glu-B2 loci (0.54). The germplasm analyzed exhibited allelic variation in HMW and LMW glutenin subunit composition and the variation differed from that of tetraploid wheats of other countries. The presence of high quality alleles in glutenin loci have led the accessions to be considered as an asset in breeding programs aimed for wheat quality.

Conferring resistance to pre-harvest sprouting in durum wheat by a QTL identified in Triticum spelta

Pre-harvest sprouting (PHS) causes significant yield loss and degrade the end-use quality of wheat, especially in regions with prolonged wet weather during the harvesting season. Unfortunately, the gene pool of Triticum durum (tetraploid durum wheat) has narrow genetic base for PHS resistance. Therefore, finding out new genetic resources from other wheat species to develop PHS resistance in durum wheat is of importance. A major PHS resistance QTL, Qphs.sicau-3B.1, was mapped on chromosome 3BL in a recombinant inbred line population derived from ‘CSCR6’ (Triticum spelta), a PHS resistant hexaploid wheat and ‘Lang’, a PHS susceptible Australian hexaploid wheat cultivar. This QTL, Qphs.sicau-3B.1, is positioned between DArT marker wPt-3107 and wPt-6785. Two SCAR markers (Ph3B.1 and Ph3B.2) were developed to track this major QTL and were used to assay a BC2F8 tetraploid population derived from a cross between the durum wheat ‘Bellaroi’ (PHS susceptible) and ‘CSCR6’ (PHS resistant). Phenotypic assay and marker-assisted selection revealed five stable tetraploid lines were highly PHS resistant. This study has successfully established that PHS-resistance QTL from hexaploid wheat could be efficiently introgressed into tetraploid durum wheat. This tetraploid wheat germplasm could be useful in developing PHS resistant durum cultivars with higher yield and good end-use quality.

Genetic dissection of quantitative powdery mildew resistance loci in tetraploid wheat

Durum wheat, Triticum turgidum ssp. durum Desf., is an important crop particularly in the Mediterranean basin. Powdery mildew, caused by the pathogen Blumeria graminis f. sp. tritici (Bgt), is a major disease of wheat that results in significant yield losses worldwide. A recombinant inbred line (RIL) population, derived from a cross between durum wheat and wild emmer wheat, T. turgidum ssp. dicoccoides, was used for genomic dissection of quantitative and qualitative resistance loci against wheat powdery mildew based on a genomic map of >600 markers, evenly distributed across the A and B genomes of tetraploid wheat. The genetic analysis of the phenotypic reactions of the RIL population to two Bgt isolates revealed two different resistance mechanisms. The first is monogenic: a wild emmer wheat allele in a single locus conferring complete resistance to Bgt#15, previously designated as PmG16. The second one is polygenic: a set of durum wheat alleles, in five independent QTLs that control partial resistance to Bgt#66 in the RIL population, with a LOD score range of 3.4–19.8. One of them is a major quantitative resistance locus (QRL) that was mapped on chromosome 1A and explains 26.4 % of the variance. In most of the detected QRLs, the durum wheat alleles conferred resistance to powdery mildew. These findings are exceptional in the sense that, so far, only a few Pm alleles originated from a durum wheat background. Therefore, our results emphasize the high potential of exploiting the wide genetic diversity of tetraploid wheat germplasm for wheat breeding using modern wheat genomics tools.

Wild Tetraploid Wheat (Triticum turgidum L.) Response to Heat Stress

Identifying reliable screening tools and characterizing tolerant germplasm sources are essential for developing wheat (Triticum aestivum L.) varieties suited for the hot areas of the world. Our objective was to evaluate heat tolerance of promising wild tetraploid wheat (Triticum turgidum L.) accessions that could be used as sources of heat tolerance in common- and durum-wheat (Triticum durum) breeding programs. We screened 16 wild tetraploid wheat accessions and two common wheat checks for their response to heat stress by measuring damage to the thylakoid membranes, flag leaf temperature depression (FLTD), and spike temperature depression (STD) during exposure to heat stress for 16 days post-anthesis (DPA). Measurements were taken on the day of anthesis then 4, 8, 12, 16 DPA under controlled optimum and heat-stress conditions. Individual kernel weight (IKW) and heat susceptibility index (HSI) measurements were also obtained. Prolonged exposure to heat stress was associated with increased damage to thylakoid membranes, as indicated by the high ratio of constant fluorescence (O) to peak variable fluorescence (P). Some wild tetraploid wheat accessions exhibited a better HSI than the common heat-tolerant wheat cultivar ‘Kauz.’ A positive and significant correlation was found between O/P ratio and each of FLTD and STD under heat-stress conditions. A negative and significant correlation was found between FLTD and HSI and between STD and HSI based on the second and third measurements (4 and 8 DPA). Correlations obtained after the third measurement were not significant because of heat-induced, accelerated maturity and a lack of green leaf tissue. This study identified potential heat-tolerant wild tetraploid wheat germplasm that can be incorporated into wheat breeding programs to improve heat tolerance in cultivated common and durum wheat.

Patterns of phenotypic diversity for phenologic and qualitative traits in Ethiopian tetraploid wheat germplasm

A total of 4,840 entries of tetraploid wheat germplasm collections representing 121 accessions from Ethiopia were evaluated for phenologic and qualitative trait diversity. The objectives were to assess the diversity patterns of the germplasm with respect to regions, species and altitudinal class. High values of Shannon–Weaver Diversity Index (H′) were recorded for most traits in each region, altitudinal classes, and species. Monomorphism was also high at accession levels. Both H′ and Nei’s gene diversity value for the entire data set (total gene diversity H T = 0.572; the within accessions gene diversity H S = 0.112; and gene diversity among accessions D ST = 0.460) showed the variation for the trait is mainly among accessions/populations rather than within accessions/population. The least mean H′ value over all the traits used for the study was obtained from released varieties (among the origin groups) and Triticum dicoccon (among species). Triticum durum exhibit the highest H′ for a number of traits. Accessions collected from altitudinal class III (2401–2800 m a.s.l.) and class II (2001–2400 m a.s.l.) showed the highest H′ values for a valuable number of traits. Thus classifications using various phenology and qualitative traits enable to identify adaptation of a genotype and would improve the evaluation of genotype for potential adaptation.

Diversity of Ethiopian tetraploid wheat germplasm: breeding opportunities for improving grain yield potential and quality traits

In this paper, Shannon–Weaver diversity indices were employed to examine the phenotypic diversity in 271 Ethiopian tetraploid wheat accessions in relation to characters, regions of origin and altitude. Moreover, review of genetic diversity studies in Ethiopian tetraploid wheat was made to explore breeding opportunities. The diversity index varied widely across regions. Among the four altitudinal classes, the highest (0.72) and lowest (0.61) mean diversity indices were observed in altitude classes II and IV, respectively. The diversity index (H′) showed that most traits are polymorphic. The partitioning of the total phenotypic diversity into within- and among-region diversity indicated that 71% of the total variation was attributed to the within-region diversity. Principal component analysis was computed to examine the regional and altitudinal patterns of variation. On regional bases, the first four axes, whose eigenvalues are greater than 1, explained about 82% of the observed phenotypic diversity in the 271 tetraploid wheat accessions. On altitudinal bases, however, only the first two principal components explained 89.7% of the total variation. In general, phenotypic diversity showed considerable differences for each trait in different geographical regions and altitudinal classes which could be utilized in wheat improvement programmes. Breeding opportunities and strategies are suggested.

Evaluation of Fusarium Head Blight Resistance in Tetraploid Wheat (Triticum turgidum L.)

Durum wheat (Triticum turgidum L. subsp. durum) production in North America in recent years has been seriously threatened by epidemics of Fusarium head blight (FHB), caused mainly by Fusarium graminearum Schwabe [teleomorph Gibberella zeae (Schw.) Petch]. Deployment of FHB‐resistant cultivars has been considered the most effective and cost‐efficient strategy to combat this disease; however, progress in developing FHB‐resistant durum wheat cultivars has been hindered by a lack of effective sources of resistance. The objective of this study is to identify tetraploid wheat germplasm that could be used to enhance FHB resistance in durum wheat. We evaluated FHB reactions in 376 accessions of five cultivated subspecies of T. turgidum, including Persian wheat [T. turgidum subsp. carthlicum (Nevski) Á. Löve and D. Löve], cultivated emmer wheat [T. turgidum subsp. dicoccum (Schrank ex Schübler) Thell.], Polish wheat [T. turgidum subsp. polonicum (L.) Thell.], Oriental wheat [T. turgidum subsp. turanicum (Jakubz.) Á. Löve and D. Löve], and Poulard wheat (T. turgidum L. subsp. turgidum). We used point inoculation to evaluate resistance to the spread of infection over three greenhouse seasons and used the grain inoculum method of inoculation to evaluate putatively resistant accessions in two field locations. Preliminary evaluation data showed that 16 T. turgidum subsp. carthlicum and 4 T. turgidum subsp. dicoccum accessions consistently exhibited resistance or moderate resistance to FHB. These accessions likely carry genetic resistance to FHB and could be used directly in breeding programs to enhance FHB resistance in durum wheat.

Variation in gluten strength and yellow pigment in Ethiopian tetraploid wheat germplasm

Ten released varieties and one hundred and eleven tetraploid (2n = 4x = 28, AABB) wheat accessions collected from different major wheat producing regions, consisting of totally 2904 entries were characterized for content of yellow pigment, gluten strength, thousand kernel weights, grain yield, percent of yellow berry, glumes color, awn color, seed color, beak shape and spike density. The objectives were to assess variation with respect to regions of origin, species and altitudinal classes and to study the interrelationships of the qualitative traits used for the study. The accessions and/or released varieties showed significant regional variation for all the traits used in the study, but clinal variation among altitudinal classes and species were significant (P ≤ 0.01) in 6 (60%) and 9 (90%) of the studied traits, respectively. The accessions revealed consistent variation (P ≤ 0.001) within both regions and altitudinal classes for all the traits used in the study. The sedimentation volume was positively correlated with content of yellow pigment, percent of yellow berry, thousand kernel weights, glumes color, awn color, beak shape, seed color and grain yield. The contents of yellow pigment was positively correlated with awn color, beak shape and grain yield, but negatively correlated with seed color and spike density. Generally wide variation was found in the germplasm. Particularly variation was high for the content of the yellow pigment as well as the gluten strength, which provides opportunities to be utilized for genetic improvement.

Composition of and variation in high- and low-molecular weight glutenin subunits, and omega gliadins in Ethiopian tetraploid wheat germplasm

A collection of 120 Ethiopian tetraploid wheat accessions was analysed for high-molecular weight (HMW) glutenin subunit, low-molecular weight (LMW) glutenin subunit and omega gliadin composition by SDS–PAGE. For the HMW glutenin subunits, a new allelic variant, 2****, was detected which has not been previously described at the Glu-A1 locus. A high proportion of Glu-A1x banding pattern was observed in durum wheat. For the Glu-B1 locus four different banding patterns were detected. Among those HMW glutenin subunits, 7+8 were the most common, while subunits 14+15 and 6+8 were found to be rare. A high degree of variation was evident for the LMW glutenin subunits and D-zone omega gliadins. The association of the composition of the gluten with quality has been discussed. This wide variation can be used in improving the quality of wheat and to widen its genetic base.

Multivariate Analysis of Diversity of Tetraploid Wheat Germplasm from Ethiopia

The variability of 2420 plants of tetraploid (2n = 4x = 28, AABB genome) wheat germplasm representing 121 accessions from Ethiopia were evaluated for 23 agro-morphological traits at Debre Zeit Agricultural Research Center area, Akaki substation, during the 2003 main season using multivariate methods. This enabled to assess the extent and pattern of variation of the germplasm with respect to regions, altitude classes and species and to identify the major traits contributing to the diversity. The first three and two principal components explained about 83 and 80% of the total variance among regions and altitudinal class, respectively. In the first principal component plant height, days to heading, the length and density of the spike, and kernel color were the most important traits contributing to variation that explained about 50% of regional variance. Cluster analysis grouped the accessions into 15 clusters, with 9 accessions remaining ungrouped. Based on the observed patterns of variation, it is concluded that there exists great variation in the germplasm, which provides opportunities to be utilized for genetic improvement.

Genetic diversity in Ethiopian hexaploid and tetraploid wheat germplasm assessed by microsatellite markers

The genetic diversity of a subset of the Ethiopian genebank collection maintained at the IPK Gatersleben was investigated applying 22 wheat microsatellites (WMS). The material consisted of 135 accessions belonging to the species T. aestivum L. (69 accessions), T. aethiopicum Jacubz. (54 accessions) and T. durum Desf. (12 accessions), obtained from different collection missions. In total 286 alleles were detected, ranging from 4 to 26 per WMS. For the three species T. aestivum, T. aethiopicum and T. durum on average 9.9, 7.9 and 7.9 alleles per locus, respectively, were observed. The average PIC values per locus were highly comparable for the three species analysed. Considering the genomes it was shown that the largest numbers of alleles per locus occurred in the B genome (18.4 alleles per locus) compared to A (10.1 alleles per locus) and D (8.2 alleles per locus) genomes. Genetic dissimilarity values between accessions were used to produce a dendrogram. All accessions could be distinguished, clustering in two large groups. Whereas T. aestivum formed a separate cluster, no clear discrimination between the two tetraploid species T. durum and T. aethiopicum was observed.

A locus for sodium exclusion (Nax1), a trait for salt tolerance, mapped in durum wheat.

Salinity affects durum wheat [Triticum turgidum L. ssp. durum (Desf.)] more than it affects bread wheat (Triticum aestivum L.), and results in lower yield for durum wheat cultivars grown on salt-affected soils. A novel source of salt tolerance in the form of a sodium exclusion trait, identified previously in a screen of tetraploid wheat germplasm, was mapped using a QTL approach. The trait, measured as low Na+ concentration in the leaf blade, was mapped on a population derived from a cross between the low Na+ landrace and the cultivar Tamaroi. The use of AFLP, RFLP and microsatellite markers identified a locus, named Nax1 (Na exclusion), on chromosome 2AL, which accounted for approximately 38% of the phenotypic variation in the mapping population. Markers linked to the Nax1 locus also associated closely with low Na+ progeny in a genetically unrelated population. A microsatellite marker closely linked to the Nax1 locus was validated in genetically diverse backgrounds, and proven to be useful for marker-assisted selection in a durum wheat breeding program.

Characterization of tetraploid wheat germplasm for resistance to Pseudocercosporella herpotrichoides, cause of eyespot disease

Eyespot disease, caused by Pseudocercosporella herpotrichoides, can be devastating to winter wheat grown in northern Europe and the northwest USA. Accessions from eight different tetraploid wheat species randomly extracted from core collections were scored for resistance to eyespot disease using a β-glucuronidase (GUS)-transformed strain of P. herpotrichoides. The GUS values for the combined population followed a quasi-Gaussian distribution. Three species, Triticum dicoccoides, T. durum and T. turanicum, showed significant variation (P < 0.001) in disease response with T. dicoccoides having the lowest disease scores, i.e. highest levels of resistance. All tetraploid accessions were less resistant than resistant diploid T. tauschii accessions. Thirteen percent of tetraploid accessions had disease scores that ranged between the average of the resistant accessions of T. tauschii and the moderately resistant hexaploid germplasm line Cerco. Eight accessions (three accessions of T. dicoccoides, two of T. turgidum and three of T. durum) with low disease scores (resistance) to infection were selected for further genetic analysis.

Resistance of Triticum dicoccoides Collected in Israel to Infection with Puccinia recondita tritici1

Triticum dicoccoides (Koern. ex Aschers. and Graebn.) Aaronsohn, a progenitor of hexaploid wheat (Triticum aestivum L.) and tetraploid wheat (Triticum turgidum L. var. durum), grows wild in many sites in Israel. Reactions were determined of 687 accessions of T. dicoccoides from that country to infection with culture PRTUS6 of Puccinia recondita Rob. ex Desm. f. sp. tritici, which incites the disease wheat leaf rust. Fourteen percent (or 98 accessions) were at least moderately resistant in the first‐leaf stage to infection with culture PRTUS6. Nineteen of 34 accessions collected at site 12 were moderately resistant as were 10 of 35 from Site 2 and four of nine from Site 8. Resistant accessions were obtained in low frequencies from Sites 6 and 7. Resistant and moderately resistant accessions were obtained among 353 accessions collected at approximately 180 sites throughout the region from Upper and Lower Galilee, Mt. Gilboa and the Judean Mountains, and Mt. Hermon and the Golan Heights. Additional resistant and moderately resistant accessions of T. dicoccoides could probably be obtained by collecting from additional sites. The resistant accessions identified in this study are being used to develop enhanced hexaploid and tetraploid wheat germplasm resistant to P. recondita tritici, Erysiphe graminis DC. ex Merat. f. sp. tritici (Em. Marchal), and P. stri‐iformis West.

Genetic Diversity in Hexaploid and Tetraploid Wheat Genotypes Using Microsatellite Markers

The genetic diversity of a set of hexaploid and tetraploid wheat germplasm at the IPK gene bank, Gatersleben, Germany was investigated by applying 13 wheat microsatellites (WMS). The materials consisted of 63 accessions of Triticum aestivum, T. dicoccon and T. durum obtained from different collection missions. In total, 126 alleles were detected with an average of 9.7 alleles per locus. The average PIC values per locus varied from 0.65 for the marker Xgwm192 to 0.88 for the marker Xgwm619. All the primer pairs revealed genetic heterogeneity in more than one genotype. Genetic dissimilarity values between genotypes, calculated by the WMS derived data, were used to produce a dendrogram. In the dendrogram the genotypes were clustered in nine clear groups. Key words: Genetic diversity, Microsatellite markers, Hexaploid, Tetraploid, Wheat genotype D.O.I. 10.3329/ptcb.v18i1.3267 Plant Tissue Cult. &amp; Biotech. 18(1): 65-73, 2008 (June)