INSTITUT FÜR PFLANZENGENETIK UND KULTURPFLANZENFORSCHUNG (IPK)
Corrensstraße 3, 06466 Gatersleben, Germany.
A. Börner, N. Iqbal, E.K. Khlestkina, S. Landjeva, U. Lohwasser, S. Navakode, K. Neumann, E.G. Pestsova, M.S. Röder, M.R. Simon, A. Weidner, and K. Zaynali Nezhad.
PCR assays specific for the GA-insensitive dwarfing genes (alleles) Rht-B1b and Rht-D1b were used to study a series of additional alleles of Rht-B1 and Rht-D1. The amplification profiles of Rht-B1b and Rht-B1d were not distinguishable from one another, whereas lines carrying Rht-B1c, Rht-B1e, and Rht-B1f amplified a product similar to that of the wild type. At the 4D locus, no discrimination was possible between Rht-D1b, Rht-D1c, and Rht-D1d. As a result, the utilization of these PCR assays is limited and additional sequencing activities are necessary.
Recently, a major gene determining nonspecific, adult-plant disease resistance to stripe rust designated Yrns-B1 was mapped in wheat using a cross between 'Lgst. 79-74' (resistant) and 'Winzi' (susceptible). Linkage to five Gatersleben wheat microsatellite (GWM) markers was discovered, previously mapped on chromosome arm 3BS. This map was improved by the incorporation of four additional GWM markers. QTL analysis revealed high LOD values for the resistance at all nine loci, whereas the largest LOD (20.76) was found for the newly mapped marker Xgwm1329.
Microsatellite analysis and resistance tests of a collection of old German/UK wheat cultivars, including probable ancestors of Lgst.79-74 were made. A high coincidence of nonspecific, adult-plant disease resistance to stripe rust and the presence of an Lgst.79-74 allele (117 bp) of the marker Xgwm533 was observed among the cultivars tested. Linkage during the inheritance of both the resistance and the 117-bp allele of Xgwm533 was demonstrated. Carriers of this resistance gene have been grown in Germany on large areas for more than 100 years.
To estimate the capability of Xgwm533 as a diagnostic marker for nonspecific adult-plant disease resistance to stripe rust, microsatellite analysis and resistance tests on a collection of Russian spring wheat cultivars were made. The 117-bp allele of Xgwm533 was found in about 35% of the Russian cultivars analyzed, however, none possessed the expected disease resistance. Thus, the utilization of Xgwm533 as diagnostic marker seems to be restricted to certain gene pools.
Bread wheat/Ae. markgrafii introgression lines expressing leaf rust resistance were developed from a cross between a leaf rust-resistant Ae. markgrafii accession and the susceptible bread wheat cultivar Alcedo. The content of the introgressed segments present in five sister introgression lines was assessed with the help of chromosome-specific SSRs. One of the lines was used as a parent of a 140-line, individual F2 mapping population by crossing with the leaf rust-susceptible bread wheat cultivar Borenos. The population was tested for susceptibility or resistance to leaf rust, and linkage analysis indicated the presence of a QTL (QLr.ipk-2A), originating from the Ae. markgrafii parent, mapping to the distal segment of chromosome arm 2AS.
At the IPK Gatersleben, a series of 84 bread wheat/goatgrass (Ae. tauschii) introgression lines was developed recently. Based on the knowledge that chromosome 7D of this particular Ae. tauschii is a donor of resistance to Septoria tritici blotch, a subset of 13, chromosome-7D introgression lines was investigated along with the susceptible recipient cultivar Chinese Spring and the resistant donor line CS (Syn 7D). The material was inoculated with two Argentinian isolates of the pathogen (IPO 92067 and IPO 93014) at both the seedling (two leaf) and adult (tillering) stages at two locations over two years (2003 and 2004). The resistance was effective against both isolates and at both developmental stages, and the resistance locus maps to the centromeric region of chromosome arm 7DS. On the basis of its relationship with the microsatellite marker Xgwm44, it is likely that the gene involved is Stb5. Stb5 is, therefore, apparently effective against M. graminicola isolates originating from both Europe and South America.
The set of 84 wheat/Ae. tauschii introgressions lines is available on request.
A QTL approach was applied to dissect the complex genetic control of plant growth response to osmotic stress in common wheat. A set of 114 RILs of the wheat International Triticeae Mapping Initiative (ITMI) mapping population were subjected to osmotic stress, induced by 12% polyethylene glycol (PEG 6000) from the onset of germination to day 8 of seedling development. Root, coleoptile, and shoot length, and root/shoot length ratio were compared under stress and control conditions. A total of 35 regions on 10 chromosomes contributed effects on seedling growth traits. Almost half of the QTL (16) were detected in controls, 17 under osmotic stress conditions, and two QTL corresponded to tolerance index. In regions on five chromosome arms (1AS, 1BL, 2DS, 5BL, and 6BL) the QTL detected under stress co-mapped with QTL for the same trait under control conditions, so they were classified as QTL affecting seed vigor per se. A wide chromosome region on chromosome 1AL, comprising five QTL with major impact of markers Glu1A (LOD 3.93) and Xksuh9d (LOD 2.91), positively affected root length under stress and the tolerance index for root length, respectively. A major QTL (LOD 3.60), associated with marker Xcdo456a in the distal part of chromosome arm 2DS, was detected for tolerance index for shoot length. Three minor QTL (LOD <3.0) for root length and root/shoot length ratio under osmotic stress were identified in the distal part of chromosome arms 6DL (marker Xksud27a) and 7DL (marker Xksue3b). Selecting for the favorable alleles at marker loci associated with the detected QTL for growth traits may be an efficient approach for increasing the ability of plants to maintain growth of roots, coleoptile, and shoots under water deficit stress at critical early developmental stages.
A set of 20, high-yielding wheat cultivars was compared with a set of preselected Genebank accessions varying in their response to salt stress, the salt-tolerant Indian landrace Kharchia, and the derived tolerant cultivar Kharchia 65. The high-yielding wheat cultivars were released in Germany before 1950 and between 1950 and 1969, 1970 and 1989, and 1990 and 2005.
Experiments were performed at the germination stage (climate chamber) and seedling stage (hydroponics, greenhouse); both with two replications. A germination test was made on filter paper (0, 1, 1.5, and 2 % NaCl; 20°C; 12-hour light/dark photoperiod; 10 days; score 0-9). For the greenhouse experiment, plant material was pregerminated in a climate chamber on moistened filter paper in the dark at 22°C for 4 days. Fifteen young, healthy plants/cultivar accession with normal growth habit were selected for hydroponics (greenhouse, 20°C, 12-hour light/dark photoperiod, 50 % Hoagland's solution). Plant boxes were covered with perforated aluminium foil, which allowed the plants to hang the roots into the solution for nutrient uptake. After a 1-week adaptation time, the nutrient solution was increased to full concentration (100% Hoagland's solution) and the stress variant was subjected to additional 100 mM NaCl. Ten days after stress initiation, shoot and root length and the fresh weight of the biomass were measured.
Germination tests clearly showed a higher tolerance of the wheat cultivars released before 1950. High-yielding cultivars released during the last 15 years were more sensitive. The comparison of the material at the seedling stage was based on the tolerance index (character under stress condition / character in control * 100). The index of the shoot length decreased from cultivars released before 1950 to modern cultivars of present time, which agrees with findings of the germination test. No clear differences were noted within the cultivars with respect to the shoot fresh weight. Most of the cultivars reacted more tolerant than Kharchia 65.
Aluminum toxicity is a major problem for cereal production worldwide, especially in the tropics. A nutrient solution culture approach was used to classify the wheat aluminium tolerance, based on the root growth of the seedlings. We investigated cytogenetic stocks of T. aestivum subsp. aestivum cultivar Chinese Spring, single-chromosome substitution lines available at IPK Gatersleben. As a result, a set of DH lines derived from the cross between 'Chinese Spring / Synthetic 3B' was used to dissect the QTL involved in aluminum tolerance. In order to construct a genetic map for chromosome 3B, the parents were screened for polymorphism using Gatersleben Wheat Microsatellite markers followed by genotyping of the DH lines, linkage analysis, and QTL detection.
A set of 114 RILs of the ITMI mapping population was evaluated for the domestication traits preharvest sprouting and dormancy. Under field conditions, major QTL could be localized for preharvest sprouting on chromosome 4AL and for dormancy on chromosome 3AL. Under greenhouse conditions, a main QTL on chromosome 4AL was found for both traits. But the major QTL on chromosome 3AL could not be detected again. In order to find the cereal genome regions responsible in general, two barley mapping populations were evaluated for both traits as well. Ninety-four DH lines of the OWB-population (Oregon Wolfe Barley) and 150 DH lines of the 'Steptoe / Morex' mapping population were grown under field and greenhouse conditions in Gatersleben. QTL for preharvest sprouting and dormancy were detected on chromosome 5H and 7H in the centromeric region. When the data were compared, there is no correlation between wheat and barley.
M.S. Röder and X.Q. Huang.
The previously described QTL for grain weight QTgw.ipk-7D associated with microsatellite marker Xgwm1002-7D was originally detected in a BC2F3 advanced backcross population of the German winter wheat cultivar Prinz and the synthetic wheat line W-7984 (lab designation: M6) (Huang et al. 2003). We developed NILs with introgressions of M6 in the genetic background of Prinz with varying sizes on chromosome 7D. The BC4F3 NILs had a 10% increased 1,000-kernel weight compared to the control group and the recurrent parent Prinz, and 84.7% of the phenotypic variance could be explained by the segregation of marker Xgwm1002-7D. The trait increased grain weight and was strongly correlated with increased grain length and increased plant height, whereas the trait grain number/ear was stable between the NILs and the control group. The QTL QTgw.ipk-7D was delimited to the interval Xgwm295-Xgwm1002, which is located in the most telomeric bin 7DS4-0.61-1.00 in the physical map of wheat chromosome arm 7DS (Röder et al. 2007). We propose the presence of a gene modulating grain weight with the preliminary designation gw1, which has a recessive or intermediate mode of inheritance for the large grain phenotype. Furthermore, our data suggest the presence of a novel, plant-height reducing locus Rht on chromosome arm 7DS of Prinz. The two phenotypes, large grain and increased plant height, may reflect the pleiotropic action of one gene or may be caused by two linked genes. In general, our data support the concept of using nearly isogenic introgression lines for validating and dissecting QTL into single Mendelian genes, opening the way for map-based cloning of a grain-weight QTL in wheat.