Phylogenetic relationships and intraspecific variation of D-genome Aegilops L. as revealed by RAPD analysis

RAPD analysis was carried out to study the genetic variation and phylogenetic relationships of polyploid Aegilops species, which contain the D genome as a component of the alloploid genome, and diploid Aegilops tauschii, which is a putative donor of the D genome for common wheat. In total, 74 accessions of six D-genome Aegilops species were examined. The highest intraspecific variation (0.03-0.21) was observed for Ae. tauschii. Intraspecific distances between accessions ranged 0.007-0.067 in Ae. cylindrica, 0.017-0.047 in Ae. vavilovii, and 0.00-0.053 in Ae. juvenalis. Likewise, Ae. ventricosa and Ae. crassa showed low intraspecific polymorphism. The among-accession difference in alloploid Ae. ventricosa (genome DvNv) was similar to that of one parental species, Ae. uniaristata (N), and substantially lower than in the other parent, Ae. tauschii (D). The among-accession difference in Ae. cylindrica (CcDc) was considerably lower than in either parent, Ae. tauschii (D) or Ae. caudata (C). With the exception of Ae. cylindrica, all D-genome species--Ae. tauschii (D), Ae. ventricosa (DvNv), Ae. crassa (XcrDcrl and XcrDcrlDcr2), Ae. juvenalis (XjDjUj), and Ae. vavilovii (XvaDvaSva)--formed a single polymorphic cluster, which was distinct from clusters of other species. The only exception, Ae. cylindrica, did not group with the other D-genome species, but clustered with Ae. caudata (C), a donor of the C genome. The cluster of these two species was clearly distinct from the cluster of the other D-genome species and close to a cluster of Ae. umbellulata (genome U) and Ae. ovata (genome UgMg). Thus, RAPD analysis for the first time was used to estimate and to compare the interpopulation polymorphism and to establish the phylogenetic relationships of all diploid and alloploid D-genome Aegilops species.     

Sequence polymorphism in polyploid wheat and their d-genome diploid ancestor

Sequencing was used to investigate the origin of the D genome of the allopolyploid species Triticum aestivum and Aegilops cylindrica. A 247-bp region of the wheat D-genome Xwye838 locus, encoding ADP-glucopyrophosphorylase, and a 326-bp region of the wheat D-genome Gss locus, encoding granule-bound starch synthase, were sequenced in a total 564 lines of hexaploid wheat (T. aestivum, genome AABBDD) involving all its subspecies and 203 lines of Aegilops tauschii, the diploid source of the wheat D genome. In Ae. tauschii, two SNP variants were detected at the Xwye838 locus and 11 haplotypes at the Gss locus. Two haplotypes with contrasting frequencies were found at each locus in wheat. Both wheat Xwye838 variants, but only one of the Gss haplotypes seen in wheat, were found among the Ae. tauschii lines. The other wheat Gss haplotype was not found in either Ae. tauschii or 70 lines of tetraploid Ae. cylindrica (genomes CCDD), which is known to hybridize with wheat. It is concluded that both T. aestivum and Ae. cylindrica originated recurrently, with at least two genetically distinct progenitors contributing to the formation of the D genome in both species.     

Analysis of relationships between Aegilops tauschii and the D genome of wheat utilizing microsatellites.

Sixty Aegilops tauschii accessions and 60 European hexaploid wheat varieties were analyzed with 14 wheat microsatellite (WMS) primer sets to (i) study the phylogeny of Ae. tauschii, (ii) search for a specific genotype of Ae. tauschii most closely related to the D genome of hexaploid wheat, and (iii) narrow down the presumed birthplace of the latter. An average of 6.5 and 4.0 alleles per locus was detected in Ae. tauschii and in wheat, respectively. The highest genetic diversity of Ae. tauschii was found in Transcaucasia and southeast of the Caspian Sea. Distribution of the 87 alleles (without null alleles) found in Aegilops did not allow differentiation of the species into the two subspecies strangulata and tauschii. Excluding null alleles, 41 alleles occurred parallel in wheat and in Aegilops. Data obtained in this study supports the view of the D genome of hexaploid wheat being a composite of several sources but does not support subsp. strangulata as the possible major source of the D genome. The highest number of region-specific alleles (three) in Ae. tauschii occurring also in the D genome of wheat, and therefore most indicative for its evolution was found in present-day Georgia, where subsp. strangulata is not endemic.     

Effects of drought and salinity on some growth-contributing parameters in wheat and barley

Summary This study is mainly concerned with some parameters contributing to growth as indicators of difference in drought resistance and salt tolerance of wheat and barley cultivars. Parameters made use of are: transpiration efficiency (‘dry matter/transpiration’ ratio), ‘leaf/root’ ratio, chlorophyll content, chlorophyll stability to heat and anatomical modifications. The results revealed that transpiration efficiency is much higher in mexican ‘super-x’ wheat than in the egyptian ‘Giza-155’ cultivar under reduced soil water matric- or osmotic potentials. Chlorophyll content increased in super-x with decreasing soil water potential while chlorophyll heat stability decreased. The reverse is true in Giza-155 cultivar. Decreased leaf/root ratio in super-x is interpretted in favour of more beneficial water balance in this cultivar. Development of more sclerenchyma in its stems supports this judgement. Of barley cultivars tested, Borg El-Arab is favoured for drought resistance and Giza-117 for salt tolerance. re]19751014     

Improvement in drought tolerance in bread wheat is related to an improvement in osmolyte production,antioxidant enzyme activities,and gaseous exchange

Water deficit stress negatively affects wheat growth, physiology, and yield. In lab and hydroponic experiments, osmotic stress levels (control, −2, −4, −6 and −8 Bars) created by PEG-6000, caused a significant decline in germination, mean germination time, root, shoot, and coleoptile length in both wheat genotypes examined. Germination was inhibited more in Wafaq-2001 than in Chakwal-50. Wafaq-2001 showed a higher susceptibility index based on root and shoot dry weight than did Chakwal-50. Wheat plants exhibited osmotic adjustment through the accumulation of proline, soluble sugars, soluble proteins, and free amino acids, and increased antioxidation activities of superoxide dismutase, peroxidase, catalase, and malondialdehyde. Increasing water deficit stress caused a linear decline in chlorophyll contents, leaf membrane stability, and relative water content in all wheat plants, with Wafaq-2001 showing a more severe negative impact on these parameters with increasing stress levels. The results suggest the possibility of utilizing some of these parameters as quantitative indicators of water stress tolerance in plants. Gas exchange measurements (photosynthesis, transpiration, stomatal conductance), leaf osmotic potential, water potential, and yield attributes decreased more abruptly with increasing water deficit, whereas leaf cuticular wax content increased in both genotypes, with more severe impacts on Wagaq-2001. More reduction in biochemical, physiological, and yield attributes was observed in Wafaq-2001 than was observed in Chakwal-50. Based on these results, we can conclude that Chakwal-50 is a more drought-tolerant genotype, and has excellent potential for future use in breeding programs to improve wheat drought tolerance.     

Hybridization of wheat and Aegilops cylindrica: development,karyomorphology, DNA barcoding and salt tolerance of the amphidiploids

The development of salt‐tolerant genotypes is key to a better utilization of salinized irrigated lands. Given the relatively low genetic diversity within the cultivated wheats for salt tolerance, exploring the Aegilops cylindrica's genetic diversity for salt tolerance is thus crucial to breed wheat for saline environments. In the current study, wheat genotypes were hybridized with Ae. cylindrica (a hyper salt-tolerant genotype), and amphidiploid plants were produced using embryo rescue and chromosome doubling techniques. Crossability and cytological examinations of amphidiploids and BC₁ were performed before sequencing the ITS4/5 and trnE/trnF DNAs to explore the phylogenetic relationships of the amphidiploids and their parents. Finally, amphidiploids were assessed for salt tolerance. Only two common wheat cultivars (‘Chinese Spring’ and ‘Roshan’) were crossable with Ae. cylindrica. The resultant intergeneric hybrids possessed 70 chromosomes, and morphologically either were similar to the male parent in ‘Chinese Spring’ × Ae. cylindrica or tended to be intermediate between parents in ‘Roshan’ × Ae. cylindrica. The phylogenetic tree divided the genotypes into two groups, in which Clade I contained Ae. cylindrica and three amphidiploids, and Clade II consisted of female parents and one amphidiploid. Amphidiploids exhibited significantly higher tolerance to salt stress compared to the female parents (wheat cultivars) in terms of a higher dry matter, lower accumulation of Na, higher K, and higher K/Na ratio in their root and leaf tissues. Taken together, the amphiploid plants might contain valuable salt tolerance factors.

     

Hybrids of Aegilops cylindrica Host with Triticum durum Desf. and T. aestivum L

The hybrids of durum and bread wheat with Ae. cylindrica have been obtained without using an embryo rescue technique. The hybrid output (of pollinated flower number) in the field conditions scored 1.0, 15.3 and 10.0% in the crosses T. durum x Ae. cylindrica, Ae. cylindrica x T. durum and T. aestivum x Ae. cylindrica, respectively. A high level of meiotic chromosome pairing between homologous D genomes of bread wheat and Aegilops has been revealed (c = 80.0-83.7%). The possibility of homoeological pairing between wheat and Ae. cylindrica chromosomes has been shown. Herewith, the correlation between the levels of homological and homoeological pairing is absent. The possibilities of genetic material interchange, including between the tetraploid species, as well as the using of Ae. cylindrica cytoplasm for durum wheat breeding are discussed.     

Characterization of chromosome-specific S-SAP markers and their use in studying genetic diversity in Aegilops species.

The short interspersed nuclear element (SINE), Au, was used to develop sequence-specific amplified polymorphism (S-SAP) markers for U- and M-genome chromosomes. The markers were localized using Triticum aestivum (wheat)-- Aegilops geniculata and wheat-- Aegilops biuncialis disomic chromosome addition lines. Thirty-seven markers distributed over 6 U and 6 M chromosomes were produced. A genetic diversity study carried out on 37 accessions from Ae. biuncialis, Ae. comosa, Ae. geniculata, and Ae. umbellulata suggested that Ae. biuncialis have arisen from its diploid ancestors more recently than Ae. geniculata. Several earlier studies indicated that the M genomes in polyploid Aegilops species had accumulated substantial rearrangements, whereas the U genomes remained essentially unmodified. However, this cannot be attributed to the preferential insertion of retroelements into the M genome chromosomes. Fourteen markers from a total of 8 chromosomes were sequenced; 3 markers were similar to known plant genes, 1 was derived from a long terminal repeat (LTR) retrotransposon, and 10 markers did not match to any known DNA sequences, suggesting that they were located in the highly variable intergenic regions.     

Root Respiration,Photosynthesis and Grain Yield of Two Spring Wheat in Response to Soil Drying

The effects of soil water regime and wheat cultivar, differing in drought tolerance with respect to root respiration and grain yield, were investigated in a greenhouse experiment. Two spring wheat (Triticum aestivum) cultivars, a drought sensitive (Longchun 8139-2) and drought tolerant (Dingxi 24) were grown in PVC tubes (120 cm in length and 10 cm in diameter) under an automatic rain-shelter. Plants were subjected to three soil moisture regimes: (1) well-watered control (85% field water capacity, FWC); (2) moderate drought stress (50% FWC) and (3) severe drought stress (30% FWC). The aim was to study the influence of root respiration on grain yield under soil drying conditions. In the experiment, severe drought stress significantly (p < 0.05) reduced shoot and root biomass, photosynthesis and root respiration rate for both cultivars, but the extent of the decreases was greater for Dingxi 24 compared to that for Longchun 8139-2. Compared with Dingxi 24, 0.04 and 0.07 mg glucose m⁻² s⁻¹ of additional energy, equivalent to 0.78 and 1.43 J m⁻² s⁻¹, was used for water absorption by Longchun 8139-2 under moderate and severe drought stress, respectively. Although the grain yield of both cultivars decreased with declining soil moisture, loss was greater in Longchun 8139-2 than in Dingxi 24, especially under severe drought stress. The drought tolerance cultivar (Dingxi 24), had a higher biomass and metabolic activity under severe drought stress compared to the sensitive cultivar (Longchun 8139-2), which resulted in further limitation of grain yield. Results show that root respiration, carbohydrates allocation (root:shoot ratio) and grain yield were closely related to soil water status and wheat cultivar. Reductions in root respiration and root biomass under severe soil drying can improve drought tolerant wheat growth and physiological activity during soil drying and improve grain yield, and hence should be advantageous over a drought sensitive cultivar in arid regions.     

远缘杂交不需幼胚培养的节节麦基因型

六倍体普通小麦(Triticum aestivum L.)是由四倍体小麦(T.turgidum L.)与二倍体节节麦(Aegilops tanschii Coss.)天然杂交然后通过染色体自然加倍形成的异源多倍体.这一起源过程是自然条件下天然发生的,它的发生需要具备一个条件:四倍体小麦与节节麦的天然杂交种子在自然条件(没有幼胚培养等)下能够正常发芽出苗.我们从22份节节麦中发现来自中东的节节麦AS60在不采用幼胚培养等人工辅助条件下,仍然很容易与四倍体小麦和普通小麦产生有生活力的杂种植株.AS60与四倍体小麦的杂交种子有50.0%(反交)及57.1%(正交)的种子,而AS60与六倍体普通小麦的杂交种子则有45.5%不需幼胚培养等措施能够正常发芽、生长.AS60的这一特征正是普通小麦起源过程需要的条件.最后探讨了这一发现对小麦遗传改良和对普通小麦起源演化研究的意义.     

Effect of water deficit on carbohydrate status and enzymes of carbohydrate metabolism in seedlings of wheat cultivars

The effect of water deficit on carbohydrate status and enzymes of carbohydrate metabolism (alpha and beta amylases, sucrose phosphate synthase, sucrose synthase, acid and alkaline invertases) in wheat (Triticum aestivum L.) was investigated in the seedlings of drought-sensitive (PBW 343) and drought-tolerant (C 306) cultivars. The water deficit was induced by adding 6% mannitol (water potential -0.815 Mpa) in the growth medium. The water deficit reduced starch content in the shoots of tolerant seedlings as compared to the sensitive ones, but increased sucrose content in the shoots and roots of tolerant seedlings, indicating their protective role during stress conditions. It also decreased the alpha-amylase activity in the endosperm of seedlings of both the cultivars, but increased alpha and beta amylase activities in the shoots of tolerant ones. Sucrose phosphate synthase (SPS) activity showed a significant increase at 6 days of seedling growth (DSG) in the shoots of stressed seedlings of tolerant cultivar. However, SPS activity in the roots of stressed seedlings of sensitive cultivar was very low at 4 DSG and appeared significantly only at day 6. Sucrose synthase (SS) activity was lower in the shoots and roots of stressed seedlings of tolerant cultivar than sensitive ones at early stage of seedling growth. Higher acid invertase activity in the shoots of seedlings of tolerant cultivar appeared to be a unique characteristic of this cultivar for stress tolerance. Alkaline invertase activity, although affected under water deficit conditions, but was too low as compared to acid invertase activity to cause any significant affect on sucrose hydrolysis. In conclusion, higher sucrose content with high SPS and low acid invertase and SS activities in the roots under water deficit conditions could be responsible for drought tolerance of C 306.     

Wheat-Aegilops biuncialis amphiploids have efficient photosynthesis and biomass production during osmotic stress

Osmotic stress responses of water content, photosynthetic parameters and biomass production were investigated in wheat-Aegilops biuncialis amphiploids and in wheat genotypes to clarify whether they can use to improve the drought tolerance of bread wheat. A decrease in the osmotic pressure of the medium resulted in considerable water loss, stomatal closure and a decreased CO₂ assimilation rate for the wheat genotypes, while the changes in these parameters were moderate for the amphiploids. Maximal assimilation rate was maintained at high level even under severe osmotic stress in the amphiploids, while it decreased substantially in the wheat genotypes. Nevertheless, the effective quantum yield of PS II was higher and the quantum yield of non-photochemical quenching of PS II and PS I was lower for the amphiploids than for the wheat cultivars. Parallel with this, higher cyclic electron flow was detected in wheat than in the amphiploids. The elevated photosynthetic activity of amphiploids under osmotic stress conditions was manifested in higher biomass production by roots and shoots as compared to wheat genotypes. These results indicate that the drought-tolerant traits of Ae. biuncialis can be manifested in the wheat genetic background and these amphiploids are suitable genetic materials for improving drought tolerance of wheat.     

小麦叶锈病新抗源筛选

小麦叶锈病是小麦生产的主要病害之一,发病严重时往往导致大幅度减产。叶锈菌生理小种的变异易导致抗病基因抗性的丧失,因此不断获得新抗源对小麦抗病育种至关重要。小麦近缘植物中含有丰富的小麦育种所需的抗病基因。本研究从小麦-近缘植物双二倍体、附加系、代换系或易位系等创新种质中筛选出小麦叶锈病新抗源,为利用这些新抗源打下基础。苗期对116份供试材料人工接种美国堪萨斯州流行的小麦叶锈菌混合生理小种 (Lrcomp) ,其中部分材料人工接种09-9-1441-1等5个中国当前流行的叶锈菌生理小种进行抗性鉴定,筛选获得新抗源。116份种质中,31份免疫、近免疫或高抗Lrcomp。含有希尔斯山羊草、尾状山羊草、拟斯卑尔脱山羊草、两芒山羊草、卵穗山羊草、沙融山羊草、柱穗山羊草、顶芒山羊草、小伞山羊草、偏凸山羊草、中间偃麦草、茸毛偃麦草、长穗偃麦草、粗穗披碱草、栽培黑麦、非洲黑麦、提莫菲维染色质的部分种质免疫或高抗Lrcomp,而含二角山羊草、无芒山羊草、沙生冰草、多年生簇毛麦和一年生簇毛麦染色质的种质表现中感至高感Lrcomp。希尔斯山羊草4S染色体、尾状山羊草C#1和D#1染色体和两芒山羊草、顶芒山羊草中可能含有未被报道的抗Lrcomp的新基因,值得进一步向小麦转育。小麦-粗穗披碱草1HtS.1BL罗伯逊易位系对Lrcomp及 09-9-1441-1和09-9-1426-1等5个中国当前流行叶锈菌生理小种近免疫,值得利用染色体工程等方法获得小片段抗病易位系应用于我国小麦抗叶锈育种。     

Salt tolerance potential of wild resources of the tribe Triticeae

The salt tolerance potential of variousAegilops species of different genome combinationsviz., Aegilops squarrosa, Ae. cylindrica, Ae. ovata. Ae. triuncialis, Ae. variabilis, Ae. bicornis, Ae. longissima, Ae. umbellulata, andAe. sharonensis was tested to identify the high salt-tolerant genotype(s). Screening was done in cement tanks filled with gravel and Hoagland nutrient solution. Salinity was created by mixing Na₂SO₄, CaCl₂, MgCl₂ and NaCl in the ratio of 10∶5∶1∶4 and induced by a stepwise increase in electrical conductivity number of tillers and number of leaves. Inter-and intragenomic variations for cation uptake were also significant. Species with DD and CD genome were found to be highly tolerant. Possible factors responsible for these observations have been discussed.     

Molecular analysis, cytogenetics and fertility of introgression lines from transgenic wheat to Aegilops cylindrica host

Natural hybridization and backcrossing between Aegilops cylindrica and Triticum aestivum can lead to introgression of wheat DNA into the wild species. Hybrids between Ae. cylindrica and wheat lines bearing herbicide resistance (bar), reporter (gus), fungal disease resistance (kp4), and increased insect tolerance (gna) transgenes were produced by pollination of emasculated Ae. cylindrica plants. F1 hybrids were backcrossed to Ae. cylindrica under open-pollination conditions, and first backcrosses were selfed using pollen bags. Female fertility of F1 ranged from 0.03 to 0.6%. Eighteen percent of the sown BC1s germinated and flowered. Chromosome numbers ranged from 30 to 84 and several of the plants bore wheat-specific sequence-characterized amplified regions (SCARs) and the bar gene. Self fertility in two BC1 plants was 0.16 and 5.21%, and the others were completely self-sterile. Among 19 BC1S1 individuals one plant was transgenic, had 43 chromosomes, contained the bar gene, and survived glufosinate treatments. The other BC1S1 plants had between 28 and 31 chromosomes, and several of them carried SCARs specific to wheat A and D genomes. Fertility of these plants was higher under open-pollination conditions than by selfing and did not necessarily correlate with even or euploid chromosome number. Some individuals having supernumerary wheat chromosomes recovered full fertility.     

Conferring drought-tolerant wheat genotypes through morpho-physiological and chlorophyll indices at seedling stage

The decrease in water resources due to the excessive use of water for irrigation purpose and climatic changes represents a serious world-wide threat to food security. In this regards, 50 wheat accessions were analyzed, using completely random factorial design at the seedlings stage under normal and drought stress conditions. Significant variation was detected among all accessions under both conditions. All characters studied showed variations in the mean values in water deficit environments in studied gemplasm at seedling stage. As seedling fresh weight, dry weight, relative water content, cell membrane thermo-stability, chlorophyll a & b were positively associated among themselves under drought conditions which showed the significance of these attribute for water deficit areas in future wheat breeding programs. Based on their performance, five accessions namely Aas-11, Chakwal-86, Pasban-90, Chakwal-97 and Kohistan-97 were selected as drought tolerant and three accessions namely Mairaj-08, Lasani-2008 and Gomal-2008 were selected as drought susceptible genotypes. The choice of wheat accessions based on the characteristics of the seedlings is informal, low-priced and less hassle. Likewise, the seedlings attributes exhibit moderate to high variation with an additive genetics effects on the environments. Best performance accessions under water deficit environment will be beneficial in future wheat breeding schemes and early screening for the attributes suggested in current experiment will be useful for producing best-yielded and drought-tolerance wheat genotypes to sustainable food security.     

Physiological and anatomical responses of wheat to induced dehydration and rehydration

Hydroponically grown wheat seedlings of two prominent Bulgarian cultivars (Katya and Prelom) were subjected to 48 h osmotic stress with PEG 8000 and were then rehydrated. The degree of stress was evaluated by monitoring relative water content, lipid peroxidation level, and accumulation of free proline and hydrogen peroxide in the leaves. Anatomy and ultrastructure of leaf tissue were observed under light microscopy. After imposition of stress, drought tolerant cultivar Katya displayed higher free proline content and significantly lower malondialdehyde and peroxide concentration in leaves than in the leaves of susceptible cultivar Prelom. After 24 h of rehydration Katya showed better ability to restore leaf water status and an apparent tendency towards recovery, whereas Prelom sustained higher levels of hydrogen peroxide, lipid peroxidation products and free proline and markedly low relative water content. Here, we have uncovered some of the characteristics displayed by cultivar Katya that enable it to survive and recover from severe osmotic stress. Interestingly, there was congruence between our results and the high level of cultivar Katya drought tolerance observed in the field.     

Introgression of a leaf rust resistance gene from <Emphasis Type="Italic">Aegilops caudata</Emphasis> to bread wheat

Rusts are the most important biotic constraints limiting wheat productivity worldwide. Deployment of cultivars with broad spectrum rust resistance is the only environmentally viable option to combat these diseases. Identification and introgression of novel sources of resistance is a continuous process to combat the ever evolving pathogens. The germplasm of nonprogenitor Aegilops species with substantial amount of variability has been exploited to a limited extent. In the present investigation introgression, inheritance and molecular mapping of a leaf rust resistance gene of Ae. caudata (CC) acc. pau3556 in cultivated wheat were undertaken. An F(2) population derived from the cross of Triticum aestivum cv. WL711 - Ae. caudata introgression line T291-2 with wheat cultivar PBW343 segregated for a single dominant leaf rust resistance gene at the seedling and adult plant stages. Progeny testing in F(3) confirmed the introgression of a single gene for leaf rust resistance. Bulked segregant analysis using polymorphic D-genome-specific SSR markers and the cosegregation of the 5DS anchored markers (Xcfd18, Xcfd78, Xfd81 and Xcfd189) with the rust resistance in the F(2) population mapped the leaf rust resistance gene (LrAC) on the short arm of wheat chromosome 5D. Genetic complementation and the linked molecular markers revealed that LrAC is a novel homoeoallele of an orthologue Lr57 already introgressed from the 5M chromosome of Ae. geniculata on 5DS of wheat.