Geographical variation in heading characters among wheat landraces,Triticum aestivum L., and its implication for their adaptability

Summary Heading time and its constituent traits, photoperiodic response, narrow-sense earliness and vernalization requirement, were surveyed for 158 wheat landraces. Wide varietal variation was observed in each character. Nearly half of the variation for each character was explained by a geographical difference in origin. Based on these data and the growing environments in each locality, we analyzed adaptation strategy, seen as the adjustment of heading time in terms of differences in the constituent traits, both individually and combined. The difference among localities indicated that wheat landraces had been selected for early heading as an adaptation strategy to water stress and/or high temperature in early summer. This change was caused by a reduction in photoperiodic response and narrow-sense earliness. The vernalization requirement was also reduced for adaptation to relatively mild winters. Adaptation strategy deduced from the variation within each locality was also different amongst localities. In the central region of wheat evolution, where wide variations existed in both photoperiodic response and narrow-sense earliness, the late-heading trait was achieved by either one of these traits individually or both of them combined. On the contrary, in the eastern and the western regions, wide variation in heading time was achieved by the unique combination of photoperiodic response and narrowsense earliness. A sampling strategy for wheat germ plasm is also discussed.     

Natural selection of allozyme polymorphisms: a microgeographical differentiation by edaphic,topographical, and temporal factors in wild emmer wheat (Triticum dicoccoides)

Summary Allozymic variation in proteins encoded by 47 loci was analyzed electrophoretically in 1983/4 and 1984/5 in 356 individual plants of wild emmer wheat, Triticum dicoccoides, from a microsite at Tabigha, north of the Sea of Galilee, Israel. Each year the test involved two 100-meter transects, each equally subdivided into basalt and terra rossa soil types, and comparisons were based on 16 common polymorphic loci. Significant genetic differentiation, genetic phase disequilibria, and genome organization according to soil type were found over very short distances. Our results suggest that allozyme polymorphisms in wild emmer wheat are partly adaptive, and that they differentiate at both single and multilocus structures primarily from environmental stress of such ecological factors as soil type, topography, and temporal changes, probably through aridity stress.     

Genetics of Heading Time in Wheat (TRITICUM AESTIVUM L.). II. the Inheritance of Vernalization Response

The inheritance of vernalization response was studied in crosses involving four spring wheats (Sonora 64 (S), Pitic 62 (P), Justin (J) and Thatcher (T)) and three winter wheats (Blackhull (B), Early Blackhull (E) and Extra Early Blackhull (EE)).—All winter cultivars were highly responsive to vernalization, and Pitic 62 was the only spring cultivar whose time to heading was significantly accelerated following cold treatments. When vernalized and grown under long days, spring and winter cultivars became comparable in their heading response, indicating that cold requirement is the major attribute differentiating the heading behavior of true spring and true winter wheats.—Inheritance of growth habit in the F₁ generation of a five-parent diallel cross showed dominance of the spring character in all spring x winter crosses. Depending on the cross, one or two duplicate major genes governing growth habit were detected in F₂, F₃ and backcross generations grown in the field under long days in the absence of vernalizing temperatures. In some spring x winter crosses most of the variation in heading time among spring segregates could be attributed to the effects of major genes conditioning growth habit. In other crosses the heading patterns appeared more complex, indicating that genes with smaller effects are also involved in the control of heading response under spring or summer environments.—Evidence was presented supporting the hypothesis that the cultivar Pitic 62 carries a different allele at one of the two major loci governing its spring habit. This allele was associated with some response to vernalization and acted as a dominant gene determining earliness under low temperature vernalization, but as a partially recessive gene determining lateness in the absence of vernalizing temperatures. Genotypes were assigned to five cultivars as follows: S, CC DD; P, CC D'D'; J, cc DD; B and EE, cc dd.—The presence of major and minor genes and of multiple alleles governing response to photoperiod and vernalization was discussed in relation to the genetic manipulation of the heading response and to breeding wheat cultivars with specific or broad adaptation.     

Comprehensive evaluating of wild and cultivated emmer wheat (<Emphasis Type="Italic">Triticum turgidum</Emphasis> L.) genotypes response to salt stress

Emmer wheat as the progenitor of common wheat, holds the genetic potentiality for improvement of wheat yield, quality and stress tolerance such as drought and salt. To comprehensively evaluate the salt tolerance of emmer wheat, a total of 30 traits including growth, physiology and photosynthesis related as well as K⁺ and Na⁺ content of 30 wild emmer and 14 durum wheat accessions were systematically investigated and compared between normal and saline conditions. Salt tolerance index (STI) based on multiple regression analysis of these traits was calculated and five wild emmer accessions showed high salt tolerance, which could be used as valuable resource for wheat salt tolerance improvement. Furthermore, wild emmer genotypes showed wider trait performance variation compared to durum wheat, indicating the higher genetic diversity in wild emmer wheat. Then, shoot Na⁺ content, shoot K⁺/Na⁺ ratio, root length and root surface area were identified as suitable indexes for salt tolerance evaluation. Na⁺ exclusion mechanism was found to be playing an important role in response to salt stress in emmer wheat. The salt tolerance in emmer wheat was systematically characterized here, which not only provided the elite germplasm for wheat improvement, but also provided the efficient method and some useful indexes for salt tolerance assessing.     

Natural variation of barley vernalization requirements: implication of quantitative variation of winter growth habit as an adaptive trait in East Asia

In many temperate plant species, prolonged cold treatment, known as vernalization, is one of the most critical steps in the transition from the vegetative to the reproductive stage. In contrast to recent advances in understanding the molecular basis of vernalization in Arabidopsis non-vernalization mutants or the spring growth habits of cereal crops such as wheat and barley, natural variations in winter growth habits and their geographic distribution are poorly understood. We analyzed varietal variation and the geographic distribution of the degree of vernalization requirements in germplasms of domesticated barley and wild barley collections. We found a biased geographic distribution of vernalization requirements in domesticated barley: Western regions were strongly associated with a higher degree of spring growth habits, and the extreme winter growth habits were localized to Far Eastern regions including China, Korea and Japan. Both wild accessions and domesticated landraces, the regions of distribution of which overlapped each other, mainly belonged to the moderate class of winter growth habit. As a result of quantitative evaluations performed in this study, we provide evidence that the variation in the degree of winter growth habit in recombinant inbred lines was controlled by quantitative trait loci including three vernalization genes (VRN1, VRN2 and VRN3) that account for 37.9% of the variation in vernalization requirements, with unknown gene(s) explaining the remaining two-thirds of the variation. This evidence implied that the Far Eastern accessions might be a genetically differentiated group derived for an evolutionary reason, resulting in their greater tendency towards a winter growth habit.     

Genetic diversity for drought resistance in wild emmer wheat and its ecogeographical associations

Wild emmer wheat (Triticum turgidum spp. dicoccoides (Körn.) Thell.), the tetraploid progenitor of cultivated wheat, is a potential source for various agronomical traits, including drought resistance. The objectives of this study were to characterize (1) the genetic diversity for drought resistance in wild emmer wheat, and (2) the relationship between drought responses of the wild emmer germplasm and the ecogeographical parameters of its collection sites. A total of 110 wild emmer accessions consisting of 25 populations and three control durum wheat cultivars were examined under two irrigation regimes, well-watered (’wet’) and water-limited (’dry’). Wide genetic diversity was found both between and within the wild emmer populations in most variables under each treatment. A considerable number of the wild emmer accessions exhibited an advantage in productivity (spike and total dry matter) over their cultivated counterparts. Most wild emmer wheat accessions exhibited a greater carbon isotope ratio (δ¹³C, indicating higher water-use efficiency) under the dry treatment and higher plasticity of δ¹³C relative to the cultivated controls, which may have contributed to the drought adaptations in the former. The most outstanding drought-tolerance capacity (in term of productivity under the dry treatment and susceptibility indices) was detected in wild emmer populations originated from hot dry locations. The results suggest that wild emmer has the potential to improve drought resistance in cultivated wheat.     

Genetic adaptation for vernalization requirement in Nepalese wheat and barley

A large number of accessions of covered and naked barley from eastern Nepal were grown without vernalization, and it was found that naked barley accessions were predominantly spring varieties while covered barley accessions were predominantly winter varieties. Seven accessions were subjected to a range of vernalization periods. Four naked varieties were spring varieties, although one showed some response to vernalization, but the three covered barleys were winter varieties. Although the majority of naked barleys are spring forms, they are winter sown at high altitudes and this does not conform to the distribution of naked barley described by Takahashi (1955). Wheat accessions which came from villages situated at high altitudes tended to have higher vernalization requirements than those which came from lower altitudes. This was taken to indicate local adaptation and a low movement of seeds (gene-flow) between villages. The relationship between vernalization requirement and altitude was not found in barley. Marked but contrasting regional patterns for vernalization requirement occurred in the wheat and covered barley. It was concluded that gene-flow was greater within regions than between them. This regional isolation together with environmental heterogeneity are major diversity promoting mechanisms.     

Segregation analysis of heading traits in hexaploid wheat utilizing recombinant inbred lines

The purpose of this study was to analyze the genetic segregation of heading traits in wheat using recombinant inbred lines (RILs) of hexaploid wheat, derived from Triticum aestivum cv. Chinese Spring and T. spelta var. duhameliamum. The population was examined under controlled environmental conditions as well as in the field. This strategy differentiated the effect of three genetic factors (vernalization requirement, photoperiod sensitivity and narrow-sense earliness) and identified their interactions. Correlation analysis showed that photoperiod sensitivity and narrow-sense earliness are critical for heading time in the field. Single-marker analysis using 322 molecular markers segregating among RIL detected a total of 38 linked markers for each genetic factor and heading in the field. In interval analysis, two Vrn genes (Vrn-B1 and Vrn-D1) and Ppd-B1 were mapped on chromosomes 5B, 5D and 2B, respectively. It was noticed that Vrn-B1 on 5B from the spelt wheat conferred a strong-spring habit equivalent to the homologous Vrn-A1. Quantitative trait locus analysis also showed that Ppd-B1 was not detected under the short-day condition without vernalization treatment, and that there were two types of genes for photoperiod sensitivity, dependent on and independent of vernalization treatment.     

Grain zinc, iron and protein concentrations and zinc-efficiency in wild emmer wheat under contrasting irrigation regimes

Micronutrient malnutrition, and particularly deficiency in zinc (Zn) and iron (Fe), afflicts over three billion people worldwide, and nearly half of the world’s cereal-growing area is affected by soil Zn deficiency. Wild emmer wheat [Triticum turgidum ssp. dicoccoides (Körn.) Thell.], the progenitor of domesticated durum wheat and bread wheat, offers a valuable source of economically important genetic diversity including grain mineral concentrations. Twenty two wild emmer wheat accessions, representing a wide range of drought resistance capacity, as well as two durum wheat cultivars were examined under two contrasting irrigation regimes (well-watered control and water-limited), for grain yield, total biomass production and grain Zn, Fe and protein concentrations. The wild emmer accessions exhibited high genetic diversity for yield and grain Zn, Fe and protein concentrations under both irrigation regimes, with a considerable potential for improvement of the cultivated wheat. Grain Zn, Fe and protein concentrations were positively correlated with one another. Although irrigation regime significantly affected ranking of genotypes, a few wild emmer accessions were identified for their advantage over durum wheat, having consistently higher grain Zn (e.g., 125 mg kg^?1), Fe (85 mg kg^?1) and protein (250 g kg^?1) concentrations and high yield capacity. Plants grown from seeds originated from both irrigation regimes were also examined for Zn efficiency (Zn deficiency tolerance) on a Zn-deficient calcareous soil. Zinc efficiency, expressed as the ratio of shoot dry matter production under Zn deficiency to Zn fertilization, showed large genetic variation among the genotypes tested. The source of seeds from maternal plants grown under both irrigation regimes had very little effect on Zn efficiency. Several wild emmer accessions revealed combination of high Zn efficiency and drought stress resistance. The results indicate high genetic potential of wild emmer wheat to improve grain Zn, Fe and protein concentrations, Zn deficiency tolerance and drought resistance in cultivated wheat.     

Evolution and dispersal of emmer wheat (Triticum sp.) from novel haplotypes of Ppd-1 (photoperiod response) genes and their surrounding DNA sequences

The sequence data from 5' UTR, intronic, coding and 3' UTR regions of Ppd-A1 and Ppd-B1 were investigated for a total of 158 accessions of emmer wheat landraces comprising 19 of wild emmer wheat (Triticum dicoccoides), 45 of hulled emmer wheat (T. dicoccum) and 94 of free-threshing (FT) emmer wheat (T. durum etc.). We detected some novel types of deletions in the coding regions from 22 hulled emmer accessions and 20 FT emmer accessions. Emmer wheat accessions with these deletions could produce predicted proteins likely to lack function. We also observed some novel mutations in Ppd-B1. Sixty-seven and forty-one haplotypes were found in Ppd-A1 and Ppd-B1, respectively. Some mutations found in this study have not been known, so they have potential for useful genetic resources for wheat breeding. On the basis of sequence data from the 5' UTR region, both Ppd-A1 and Ppd-B1 haplotypes were divided into two groups (Type AI/AII and Type BI/BII). Types AI and AII of Ppd-A1 suggested gene flow between wild and hulled emmer. On the other hand, Types BI and BII of Ppd-B1 suggested gene flow between wild and FT emmer. More than half of hulled emmer accessions were Type AII/BI but few FT emmer accessions were of this type. Therefore, over half of the hulled emmer did not contribute to evolution of FT emmer.     

Two-gene systems of vernalization requirement and narrow-sense earliness in einkorn wheat.

The genetic segregation of the heading trait was analyzed using a recombinant inbred line (RIL) of einkorn wheat, RILWA-1, derived from cultivated Triticum monococcum L., and wild-type T. boeoticum Boiss. The latency to heading was examined in 115 lines under controlled environmental conditions, as well as in the field, and the degrees of narrow-sense earliness and vernalization requirement were evaluated for quantitative trait locus (QTL) analysis. Single-marker analysis using 107 RFLP markers segregating in RILWA-1 detected 20 linking markers for heading factors. In all marker loci, the alleles for early heading were conferred by T. monococcum. In interval analysis of chromosome 5Am, two vernalization genes, Vrn-Am1 and Vrn-Am2, were precisely mapped to the Xcdo504-Xpsr426 interval on the central region of the long arm and to the Xwg114-Xwec87 interval on its distal region, respectively. Interval analysis also showed that two genes for narrow-sense earliness, designated Nse-3Am and Nse-5Am, were located on chromosome 3Am and 5Am, respectively. It was noticed that heading time in the field was determined mainly by Nse-3Am, suggesting that narrow-sense earliness is critical for heading in the field in einkorn wheat.     

Genetic diversity for grain nutrients in wild emmer wheat: potential for wheat improvement

Background and Aims

Micronutrient malnutrition, particularly zinc and iron deficiency, afflicts over three billion people worldwide due to low dietary intake. In the current study, wild emmer wheat (Triticum turgidum ssp. dicoccoides), the progenitor of domesticated wheat, was tested for (1) genetic diversity in grain nutrient concentrations, (2) associations among grain nutrients and their relationships with plant productivity, and (3) the association of grain nutrients with the eco-geographical origin of wild emmer accessions.

Methods

A total of 154 genotypes, including wild emmer accessions from across the Near Eastern Fertile Crescent and diverse wheat cultivars, were characterized in this 2-year field study for grain protein, micronutrient (zinc, iron, copper and manganese) and macronutrient (calcium, magnesium, potassium, phosphorus and sulphur) concentrations.

Key Results

Wide genetic diversity was found among the wild emmer accessions for all grain nutrients. The concentrations of grain zinc, iron and protein in wild accessions were about two-fold greater than in the domesticated genotypes. Concentrations of these compounds were positively correlated with one another, with no clear association with plant productivity, suggesting that all three nutrients can be improved concurrently with no yield penalty. A subset of 12 populations revealed significant genetic variation between and within populations for all minerals. Association between soil characteristics at the site of collection and grain nutrient concentrations showed negative associations between soil clay content and grain protein and between soil-extractable zinc and grain zinc, the latter suggesting that the greatest potential for grain nutrient minerals lies in populations from micronutrient-deficient soils.

Conclusions

Wild emmer wheat germplasm offers unique opportunities to exploit favourable alleles for grain nutrient properties that were excluded from the domesticated wheat gene pool.     

Differential effects of cultivated and wild barley 5H chromosomes on heading characters in wheat-barley chromosome addition lines

Wheat (Triticum aestivum L.)-barley (Hordeum vulgare L.) chromosome addition lines are possible vehicles for transferring barley genes into wheat. The barley 5H chromosome has genetic effects on the heading characters in wheat-barley addition lines: accelerating narrow-sense earliness, decreasing vernalization requirement and/or increasing photoperiodic sensitivity. To elucidate the effects of different 5H chromosomes under an identical wheat genetic background, two wheat-barley addition lines, i.e. cultivated barley 'New Golden' 5H chromosome added to 'Shinchunaga' wheat (Shi-NG5H) and wild barley H. vulgare ssp. spontaneum 5H chromosome added to 'Shinchunaga' wheat (Shi-Spn5H), were examined for their heading characters. The addition line Shi-NG5H showed a significantly lower vernalization requirement in comparison with 'Shinchunaga' wheat, whereas Shi-Spn5H did not. Furthermore, both NG5H and Spn5H chromosomes shortened narrow-sense earliness and increased photoperiodic sensitivity in wheat, but the effects of Spn5H were weaker than those of NG5H. The fact that NG5H and Spn5H showed differential effects on heading characters in wheat demonstrated that the heading characters were altered by the function of the barley genes located on 5H chromosomes, not merely by the aneuploid effect alone.     

Allelic variation at the linked AP1 and PhyC loci in hexaploid wheat is associated but not perfectly correlated with vernalization response

Vernalization requirement is an important trait in temperate crop plants such as wheat and must be considered when selecting varieties for cultivation under different climatic conditions. To determine the growth habit of wheat varieties, plants need to be grown under different vernalization regimes, a lengthy but necessary process for breeders involved in crossing winter with spring germplasm. If haplotypes can be associated with growth habit, then molecular marker assays that are reliable, cheap, and quick can be developed to assist in the selection of plants with the desired phenotype. We have analyzed 81 accessions that have different vernalization requirements and putative different origins of spring habit for sequence variation at the Apetala1 (AP1) locus, which underlies Vrn-1, and at the linked Phytochrome C (PhyC) locus. Good correspondence was found between the AP1 genotype and the PhyC haplotype for 77 of the 81 accessions. Two varieties displayed a recombination event between the AP1 and PhyC loci, and one variety carried a recombinant PhyC gene. In addition, one variety carried an apparent AP1 winter allele, but displayed the Vrn-A1 spring habit. The PhyC haplotype for this variety also indicated the presence of a Vrn-A1 spring allele. Our data suggest that both the AP1 promoter region and PhyC SNPs can be used as diagnostic markers for vernalization response at the vrn-A1 locus, but that neither are perfect tags.     

Photosynthetic performance in wild emmer wheat,Triticum dicoccoides: ecological and genetic predictability

Summary In a twin study, we have shown that wild emmer wheat, Triticum dicoccoides, the progenitor of all cultivated wheats, harbours important genetic variation (Vg) in photosynthetic characteristics. This Vg resides within and between populations and ecogeographical regions in Israel, which is the center of origin and diversity of wild emmer wheat. Here we analyzed, by univariate and multivariate methods, the significant differentiation of variation in photosynthetic characteristics of 107 genotypes from 27 populations of wild emmer in Israel, distributed in three ecogeographical regions including central, xeric (northern cold and eastern warm) marginal, and mesic (western) marginal populations. The highest photosynthetic efficiency was displayed by populations of the xeric marginal region, but most variation for photosynthetic capacity occurs between accessions within ecogeographical regions and populations. Genotypes and populations of T. dicoccoides having high photosynthetic capacity can be identified by climatic factors and isozyme markers. The identification by genetic markers, if substantiated by testcrosses, can facilitate the maximization of conservation, in situ or ex situ, and utilization of these photosynthetic genetic resources for improvement of hexaploid wheat (T. aestivum).     

A single nucleotide polymorphism at the Vrn-D1 promoter region in common wheat is associated with vernalization response

Facultative wheat varieties adapt to a particular environment. But the molecular basis for the facultative growth habit is not clear relative to winter and spring growth habit. Two sets of wheat varieties were chosen for this study. Set 1 comprised ten spring accessions and Set 2 comprised ten facultative accessions. All accessions had been tested by the previously described allele-specific markers and shown having the same allelic composition of vrn-A1 vrn-B1 Vrn-D1 and vrn-B3. Here we examined whether differences in growth habit might be associated with as yet unidentified sequence variation at Vrn-D1 locus. A region including the intron 1 deletion, the entire reading frame from a cDNA template and a part of promoter region of the dominant Vrn-D1 gene in each of the accessions was sequenced, and a single nucleotide polymorphism was found between facultative accessions and spring accessions in the CArG-box at the promoter region. The novel allele in facultative accessions was designated as Vrn-D1b. The investigation of an F₂ population segregating for Vrn-D1b and Vrn-D1a (previously, Vrn-D1) in the greenhouse under long days without vernalization showed that the plants with Vrn-D1b homozygous allele headed 32?days later and had about three more leaves than the plants with Vrn-D1a homozygous allele. As Vrn-D1b has the same deletion in intron 1 as Vrn-D1a, and, in addition, a single nucleotide mutation at promoter region, and is associated with facultative growth habit, we suggest that the promoter mutation may modify the basal activity level of an allele of VRN1 that is already active (due to the loss of segments in intron 1). Our finding further supports that both the promoter and intron 1 regulatory affect vernalization response and work independently.     

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

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