INSTITUT FÜR PFLANZENGENETIK UND KULTURPFLANZENFORSCHUNG (IPK)
Corrensstraße 3, 06466 Gatersleben, Germany.
A. Borner, A. Balint, K.F.M. Salem, U. Lohwasser, A. Weidner, M.S. Roder, and E.K. Khlestkina.
Salt tolerance. [p. 36]
Three hundred fifty-nine spring wheat accessions and 210 winter wheat accessions were tested for salt tolerance at the germination stage. Three different NaCl solutions (1 %, 1.5 %, and 2 %) and a distilled water control were used to determine the tolerance against salt stress. Spring wheat accessions from the Himalaja region of Asia have shown a high tolerance. Accessions from the northern part of Africa (Tunisia and Libya) also showed a high tolerance. In general, winter wheat possesses a higher salt tolerance in comparison to spring wheat, but no geographical connections were found.
Morphological characters of the spike are less suitable for the selection of genotypes tolerant to salt stress. A slight effect of awn length was found. Accessions with short awns reacted more tolerant than accessions with long awns.
Several control plants of tolerant and sensitive accessions selected from the germination test were further analyzed in a greenhouse experiment. The plants were transferred in pots with a soil mixture (sand and peat moss in a 2:1 ratio) and treated in three variants (water, 4 g NaCl/L, and 8 g NaCl/L) until maturity. The average yield reduction in the toleralnt accessions was 30-50 % at 4g NaCl/L and 80-90 % at 8g NaCl/L. The decrease in yield at 4g NaCl/L for sensitive accessions was more than 75 %. The sensitive wheat completely failed to develop spikes in the 8g NaCl/L treatment. The number of the tillers obviously influenced the reaction to salt stress. Plants with a high number of tillers in the control treatment tended to show a more sensitive reaction under salt stress conditions. The reaction in the germination stage was not equal to the reaction in the adult-plant stage in all cases. Therefore, germination tests are not enough to assess salt tolerance during the whole life cycle of a plant.
In addition, a set of T. aestivum/Ae. tauschii introgression lines developed at IPK was tested in order to localize chromosomal regions that affect salt tolerance. The test was carried out in the same manner as described for the screening of the wheat accessions. Interesting segments in respect to the germination in a saline environment were found on chromosome 3D, 4D, and 7D.
Post-anthesis drought tolerance. [p. 36-37]
Post-anthesis drought stress is a common problem in wheat productions. The wheat stem can function as both a source and sink for assimilates. Soluble carbohydrates usually accumulate in cereal stems and other vegetative tissues from the time of spike emergence until shortly after anthesis. Stem reserves are a major resource providing carbohydrates and nitrogen for grain filling when the transient photosynthetic source is inhibited by stress. Stem reserve mobilization was reported to be associated with post-anthesis drought tolerance. Previous studies have shown that some chemical desiccants and senescing agents, when applied to adequately watered cereals 10 to 14 days after anthesis, can be used to select lines with stable grain size (kernel weight) under post-anthesis water deficit. The present study evaluated the potential of one of these chemicals, potassium iodide (KI), to select for this character and to identify and map QTL associated with post-anthesis drought tolerance in hexaploid wheat. Quantitative trait loci analysis was carried out with a set of 114 RILs from the International Triticeae Mapping Initiative population (ITMI) of synthetic wheat 'W7984, tolerant/Mexican wheat Opata 85, sensitive' to identify the genomic regions controlling traits related to post-anthesis drought tolerance (PADT). In one experiment in Gatersleben, the amount of dry matter stored and mobilized was estimated by measuring changes in 1,000-kernal weight after a chemical desiccation treatment. The reduction in final grain weight ranged between 35.35 % and 99.77 %. We have determined the chromosomal locations of QTL affecting grain yield under drought stress on chromosomes 1B, 2D, 5D, and 7D. Also, using phenotypic data obtained after spray treatment with KI, QTL for six grain characters, i.e., area, length, width, circumference, roundness, and density, were mapped on chromosomes 1B, 2D, 5A, 7A, 3D, 4D, 5D, 2B, and 7B.
Copper tolerance. [p. 37]
Fifty-three recombinant inbred lines originated from the crossing of the hexaploid wheat Opata 85 and the synthetic hexaploid wheat W7984 were screened in the greenhouse for copper tolerance, and QTL mapping of the copper tolerance traits was performed. QTL with a great significant effect were found on the chromosomes 5DL and 7DS and with smaller effect on the chromosomes 1AL, 4AL, 2DS, 2AL, and 5BL. The role of the chromosomes 5D and 7D for Cu tolerance was reported in earlier testing of subtitution lines. These results suggest that copper tolerance is under the control of more than one chromosome, indicating the polygenic character of Cu tolerance. QTL influencing the shoot Cu, Fe, Mn, and Zn concentrations in control and a Cu-treated enviroment also were determined.
Preharvest sprouting / dormancy. [p. 37]
A set of 114 RILs of the ITMI mapping population was grown under field conditions in Gatersleben. The lines were evaluated for the domestication traits preharvest sprouting and dormancy (germinability). Main QTL could be localized for preharvest sprouting on chromosome 4AL and for dormancy on chromosome 3AL. But preharvest sprouting and dormancy in wheat are complex, involving multiple physiological risks and multiple interactions between genetic and environmental factors. Therefore, we need to retry the evaluation under constant greenhouse conditions in the coming season to eliminate the influence of weather and verify the detected QTL. Also wheat-Ae. tauschii introgression lines will be tested to discover the influence of the D genome on preharvest sprouting and dormancy.
Using microsatellite markers, samples of cultivated wheat collected in intervals of 40 to 50 years in four geographical regions of Europe and Asia (Albania, Austria, North India, and Nepal) were analyzed. No significant differences in either the total number of alleles per locus or in the PIC values were detected by comparing material from repeated collection missions in all four regions analyzed. About two-thirds of the alleles were common for both collection periods. One-third, however, represented collection mission-specific alleles. These findings demonstrate that allele flow took place during the adaptation of traditional agriculture to modern systems, whereas the level of genetic diversity was not influenced significantly. The data clearly demonstrate that in a certain period of cultivation a certain amount of unique alleles is present, which may have consequences for the conservation of plant genetic resources. The exploitation of the whole range of allelic variation makes it necessary both to maintain the already existing ex situ collections but also to collect new material.
For wheat, more than 1,000 GWM (Gatersleben Wheat Microsatellite)
markers have been developed at IPK Gatersleben or TraitGenetics
GmbH, Gatersleben, of which 651 were screened for their usability
for rye mapping, regardless of whether they represent microsatellites
or STS markers. In total, 81 primer pairs (12.4 %) amplified PCR
products of a good quality in the rye genome; 56 amplified 70
loci either polymorphic in one of the four mapping populations
(60) or located on particular chromosomes using the set of wheat-rye
addition lines (10). Comparing the locations of Xgwm loci amplified
by the same primer pairs in wheat and rye genomes, we showed that
44 out of 60 Xgwm loci mapped in orthologous positions, by considering
the multiple evolutionary translocations in the rye genome relative
to those of hexaploid wheat and the other Triticeae species. The
identification of cross-amplifying microsatellite (STS) loci is
important for their further application in comparative studies
among wheat and rye or even other cereals.
Ethiopian hexaploid and tetraploid wheat germplasm assessed by
microsatellite markers. Genet Res Crop Evol (in press).
Rajeev K. Varshney, Nils Stein, and Andreas Graner.
In the context of developing microsatellite markers in barley, a set of 111,090 barley ESTs (corresponding to 55.9 Mb) was employed for the searching of microsatellites or SSRs. With the help of a PERL5 script (MISA, http://pgrc.ipk-gatersleben.de/misa/; Thiel et al. 2003), a total of 9,564 microsatellites (EST-SSRs) were identified in 8,766 ESTs (SSR-ESTs). Cluster-analysis revealed 2,823 nonredundant SSR-ESTs (see Varshney et al. 2002). A set of 756 primer pairs for EST-derived SSRs (EST-SSRs) was analyzed in a set of seven barley genotypes (including parents of three mapping populations), and a total of 190 EST-SSRs were placed onto the barley genetic map.
Of the 165 barley microsatellites examined, 74 % showed amplification in wheat. In silico analysis of 190 barley SSR-ESTs (corresponding to mapped barley EST-SSRs) against 502,868 wheat ESTs showed the presence of homologues of 93 % barley SSR-ESTs in wheat. Furthermore, the sequences of all 190 mapped barley SSR-ESTs were compared (BLASTN) to 90 genetically mapped wheat SSR-ESTs (Mark Sorrells, personal communication). A total of 11 barley SSR-ESTs showed a significant match (< 1E-10) to wheat SSR-ESTs that were located in corresponding homoeologous linkage groups. The sequences of the same set of barley SSR-ESTs was compared further to 4,840 wheat ESTs that have been physically assigned to wheat chromosomes via deletion mapping (http://wheat.pw.usda.gov/NSF/progress_ mapping.html). Twenty-seven barley SSR-ESTs had significant homology with 23 wheat ESTs physically mapped on the corresponding homoeologous linkage groups in wheat. Altogether, 38 barley SSR-ESTs (20 %) showed the best sequence homology to 34 wheat ESTs mapped genetically or physically on homoeologous linkage groups (Table 1). Out of 38 barley SSR-ESTs, four were found to be derived from the same gene after redundancy analysis, though the EST-SSR markers were derived for different microsatellites.
| Barley chromosome | Number of barley markers | Hits with wheat ESTs | Wheat ESTs mapped | Conservation of orthologous SSR repeat motif | |
|---|---|---|---|---|---|
| Genetically | Physically | ||||
| 1H | 26 | 7 | 1 (1*) | 6 (1) | 2 (28.9 %) |
| 2H | 33 | 5 | 1 (1) | 4 (0) | 1 (20.0 %) |
| 3H | 36 | 13 | 2 (2) | 7** (1) | 3 (23.1 %) |
| 4H | 26 | 2 | 1 (0) | 1 (1) | 1 (50.0 %) |
| 5H | 22 | 3 | 1 (1) | 2 (0) | 1 (33.0 %) |
| 6H | 25 | 3 | 3 (2) | 0 (0) | 2 (66.7 %) |
| 7H | 22 | 5 | 2 (2) | 3 (0) | 2 (40.0 %) |
| Total | 190 | 38 | 11 (9) | 23 (3) | 12 (35.3 %) |
| * Number of wheat ESTs containing similar
SSR-repeat motif as of barley is given in parenthesis. ** Two of seven wheat EST showed significant homology with more than one barley SSR-ESTs. |
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In order to determine the occurrence of conserved microsatellite motifs in putatively orthologous loci between barley and wheat, in silico sequence analysis was performed on EST-contig/EST sequences of wheat. A total of 14 of 34 (41.2 %) wheat contig/ESTs contained microsatellites. However, similar SSR repeat motifs, as in barley, were present only in 12 (35.3 %) contig/ESTs (Table 1).
The above analysis indicates the potential of gene-derived microsatellite markers of barley to be transferred to wheat. However, despite the high level of transferability, the conservation of the individual microsatellite motifs is low between the two species.
References.