SummaryVirus diseases are widespread threats for crop production, which can, in many cases, be controlled efficiently by exploiting naturally occurring resistance. Barley, an important cereal species of the Triticeae, carries two genes, rym4 and rym5, which are located in the telomeric region of chromosome 3HL and confer recessive resistance to various strains of the Barley yellow mosaic virus complex. The barley 'eukaryotic translation initiation factor 4E' (Hv-eIF4E) was identified as a candidate for resistance gene function by physical mapping on a 650 kb contig. It is located in a chromosomal region characterized by suppressed recombination, in a position collinear to its homologue on rice chromosome 1L. Sequence diversity in the coding region of Hv-eIF4E, as calculated from a collection of unrelated barley accessions, revealed non-silent single nucleotide polymorphisms (SNPs) in four of its five exons. Stable transformation of a resistant barley genotype with a genomic fragment or a full-length cDNA of Hv-eIF4E derived from susceptible cultivars induced susceptibility to Barley mild mosaic virus. Moreover, the identification of SNPs diagnostic for rym4 and rym5 provides evidence that these are two alleles, which confer different resistance specificities. These findings demonstrate that variants of Hv-eIF4E confer multiallelic recessive virus resistance in a monocot species. The identification of eIF4E as the causal host factor for bymovirus resistance illustrates that mutations in this basic component of the eukaryotic translation complex form a seminal mechanism for recessive virus resistance in both dicot and monocot plants.

Soybean cultivation holds great potential for a sustainable agriculture in Europe, but adaptation remains a central issue. In this large mega-environment (MEV) study, 75 European cultivars from five early maturity groups (MGs 000-II) were evaluated for maturity-related traits at 22 locations in 10 countries across Europe. Clustering of the locations based on phenotypic similarity revealed six MEVs in latitudinal direction and suggested several more. Analysis of maturity identified several groups of cultivars with phenotypic similarity that are optimally adapted to the different growing regions in Europe. We identified several haplotypes for the allelic variants at the E1, E2, E3 and E4 genes, with each E haplotype comprising cultivars from different MGs. Cultivars with the same E haplotype can exhibit different flowering and maturity characteristics, suggesting that the genetic control of these traits is more complex and that adaptation involves additional genetic pathways, for example temperature requirement. Taken together, our study allowed the first unified assessment of soybean-growing regions in Europe and illustrates the strong effect of photoperiod on soybean adaptation and MEV classification, as well as the effects of the E maturity loci for soybean adaptation in Europe.

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Soil-borne barley yellow mosaic virus disease--caused by a complex of at least three viruses, i.e. Barley mild mosaic virus (BaMMV), Barley yellow mosaic virus (BaYMV) and BaYMV-2--is one of the most important diseases of winter barley in Europe. The two genes rym4, effective against BaMMV and BaYMV, and rym5, additionally effective against BaYMV-2, comprise a complex locus on chromosome 3HL, which is of special importance to European barley breeding. To provide the genetic basis for positional cloning of the Rym4/Rym5 locus, two high-resolution maps were constructed based on co-dominant flanking markers (MWG838/Y57c10 - MWG010/Bmac29). Mapping at a resolution of about 0.05% rec., rym4 has been located 1.07% recombination distal of marker MWG838 and 1.21% recombination proximal to marker MWG010. Based on a population size of 3,884 F2 plants (0.013% recombination) the interval harbouring rym5 was delimited to 1.49+/-0.14% recombination. By testing segmental recombinant inbred lines (RILs) for reaction to the different viruses at a resolution of 0.05% rec. (rym4) and 0.019% rec. (rym5), no segregation concerning the reaction to the different viruses could be observed. AFLP-based marker saturation for rym4, using 932 PstI+2/MseI+3 primer combinations only resulted in three markers with the closest one linked at 0.9% recombination to the gene. Two of these markers detected epialleles arising from the differential cytosine methylation of PstI sites. Regarding rym5, profiling of 1,200 RAPD primers (about 18,000 loci) and 2,048 EcoRI+3/MseI+3 AFLP primer combinations (about 205,000 loci) resulted in one RAPD marker and seven AFLP markers tightly linked to the resistance gene. Flanking markers with the closest linkage to rym5 (0.05% and 0.88% recombination) were converted into STS markers. These markers provide a starting point for chromosomal walking and may be exploited in marker-assisted selection for virus resistance based on rym5.

Chromosome analyses in human peripheral lymphocytes provide a means of estimating equivalent whole-body doses after actual or suspected over-exposure to ionizing radiations [2,7,10,14]. As a prerequisite representative calibration curves have to be established from standardized in vitro experiments.For an adequate consideration of cell proliferation kinetics on aberration yield, chromosome analyses should be carried out on cultures treated with 5-bromodeoxyuridine (BrdU) in only first-division cells (M1) , identified by fluorescence plus Giemsa staining (FPG) [8,19].For experiments with 220-keV X-rays [23] and 14.5-MeV neutrons [6] we could recently demonstrate that distinct different dose-effect curves for dicentrics and acentrics may result depending on the application of FPG-staining or conventional staining.Additionally, for calibration purposes an appropriate statistical analysis of dose-response functions must be Carried out. For an estimation of regression parameters of common models of dose-response mainly the least squares method is used. Since the variances of observed aberration yields are different at different doses, one has to account for statistical weights (reciprocal sample variance) for each observation [12].The present study reports on experiments with human lymphocytes exposed to 6°Co 7-rays at dose rates of 0.017 and 0.5 G y -m i n -1. Chromosome aberrations were scored exclusively in Ml-cells and the dose-response was analysed by applying a weighted least squares approximation.Irradiation conditions for whole blood from a healthy male donor were identical to our earlier experiments with 6°Co 7-rays [5]. A detailed description of culture conditions is given elsewhere [1,13]. A total of 29,200 Ml-cells was analysed for both experiments and the dose response for dicentrics and excess acentrics (sum of terminal and interstitial deletions + acentric rings) was determined. Since ringchromosomes were always observed in a frequency of only about one tenth of total dicentrics they were not included in the quantitative analysis. The control data are pooled from 24,000 Ml-cells of 47 unexposed persons analysed in our laboratory (0.38 dicentrics and 3.0 acentrics per 103 cells).