Powdery mildew resistance in winter barley cultivars

Powdery mildew is the most common disease of barley in the Czech Republic and winter barley plays a crucial role in the winter survival and reproduction of the pathogen. This study was aimed at identifying resistance genes in winter barley cultivars grown in the Czech Republic from 1971 to 2005 by using the method of postulation. Forty-one cultivars and a parental line were tested at the seedling stage for their reaction to 32 selected isolates of Blumeria graminis f. sp. hordei . In total, 26 resistance spectra were detected and the following 18 resistance genes were found: Mla6 , Mla7 , Mla8 , Mla13 , Mla14 , MlaMu2 , MlaNo3 , MlaRu4 , Mlg , Mlh , MlLa , Mlra , Ml ( Bw ), Ml ( Ch ), Ml ( Dr2 ), Ml ( Dt5 ), Ml ( IM9 ) and Ml ( St ). Two cultivars ('Kiruna' and 'Sorna') exhibited heterogeneity for mildew resistance. Another source of Mla13 and a possible centre of origin of Ml ( Bw ) are discussed.     

Temperature-sensitive genes for resistance to Puccinia striiformis in Triticum dicoccoides

Summary Twenty-six selections of wild emmer collected at different sites in Israel and three entries obtained from Turkey were studied for the possible presence of temperature-sensitive genes controlling reaction to Puccinia striiformis. In tests carried out in Israel with a local P. striiformis isolate at two temperature regimes, 16 selections showed a change in infection rating toward resistance at the higher temperature regime. In comparable tests performed in the United States with a Montana P. striiformis isolate of different virulence pattern-including 14 of the same selection—ten entries displayed a temperature-sensitive reaction. Although slightly different temperature regimes were used in Israel and the United States, the results obtained were in general agreement. The shift toward resistance observed in the seedling tests at the higher temperature-profile was also evident in the field in the mature plant stage with increasing spring temperatures.     

Validation of the two-gene epistatic model for vernalization response in a winter × spring barley cross

A two gene epistatic model in which a dominant “winter growth habit” allele at Vrn-H2 encodes a repressor with a corresponding binding site in a recessive vrn-H1 allele explains the vernalization response phenotypes in an array of barley germplasm. In order to validate the model genetically, we developed an F ₂ population (and F ₂-derived F ₃ families) from the cross of Hardy (winter) × Jubilant (spring). Using gene-specific primers, we determined the Vrn-H1 and Vrn-H2 allele architecture of each F ₂ plant and we measured the growth habit phenotype of each F ₂ plant via phenotyping of its F ₃ progeny under controlled environment conditions. We used a set of treatments involving plus/minus vernalization under long photoperiod and vernalization under short photoperiod. Alleles at the two loci showed expected patterns of segregation and independent assortment. Under long day conditions, the two Vrn genes were the primary determinants of heading date, regardless of the vernalization treatment. Under short photoperiod, the effects of these loci were not significant. There was incomplete dominance at Vrn-H1: heterozygotes were significantly later to head than Vrn-H1Vrn-H1 genotypes. Vrn-H2 genotypes were also significantly later to head, even when plants were vernalized. These results validate the two-gene epistatic model for vernalization response under long-day conditions. The results under short photoperiod, and the variance in flowering with vernalization, confirm that while the two Vrn genes are the primary determinants of vernalization response, they are part of a larger interactome that determines the timing of the vegetative to reproductive transition.     

Genetic mapping of the genes for glaucous leaf and tough rachis in Aegilops tauschii, the D-genome progenitor of wheat

Glaucous leaf and tough rachis phenotypes are rare in Aegilops tauschii, the D genome donor to common wheat (Triticum aestivum). The genes for glaucous leaf and tough rachis were mapped using microsatellite probes in A. tauschii. The glaucous phenotype was suppressed by the inhibitor W2^I located on chromosome 2DS. The gene W2^I was mapped to the distal part of 2DS, and was unlinked to the centromere. This suggests that the distance of the W2^I locus from the centromere was maintained during the evolution of hexaploid wheat from its diploid progenitors as the inhibitor gene is at the same position in A. tauschii and bread wheat. The Br^t (Brittle rachis of A. tauschii) locus was located on the short arm of chromosome 3D, and was 19.7 cM from the centromeric marker, Xgdm72.3D. Br^t causes breakage of the spike at the nodes, thus creating barrel-shaped spikelets, while Br₁ in hexaploid wheat causes breakage above the junction of the rachilla with the rachis such that a fragment of rachis is attached below each spikelet.     

18S.26S Ribosomal RNA Genes Are Not in Every Case Located on the B Chromosomes in the Rye Genome

To examine whether or not the 18S.26S ribosomal RNA genes are located on the B chromosomes of rye, we applied conventional and molecular cytological techniques to the B chromosomes of six rye strains, including cultivated, weedy and wild species. The results indicated that the B chromosomes in the rye genome do not generally carry repeats of the 18S.26S rRNA genes detectable at the cytological level.     

Mapping genes for resistance to sprouting damage in wheat

A series of experiments to investigate the genetic basis of pre-harvest sprouting are reported. The results are combined with previously published studies in a composite genetic map for sprout resistance in hexaploid wheat. Different studies, using classical genetics, aneuploids, chromosome substitutions, or QTL mapping, have identified various regions of the A, B, and D genomes affecting dormancy. Comparisons between the available studies lead to the following conclusions: • Different studies often identify different genetic loci, in part reflecting different sampling from the available gene pool. This implies that many loci are involved in determining resistance, and that new loci may be discovered as the number of mapping studies increases.• There are, however, examples where similar map locations are implicated over different crosses. These may reflect the detection of key resistance genes. • Finally, (genotype × environment) interactions are frequently observed. The implications of these observations for crop improvement and research programmes are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

A New Source of Resistance to Puccinia striiformis f. sp. tritici in Spring Wheats (Triticum aestivum)

The use of P. striiformis f. sp. tritici pathotypes virulent or avirulent with respect to both Yr6 and a previously undescribed source of resistance, designated YrA, allowed the recognition of the corresponding host resistance genes m a range of Australian and exotic spring wheats. The phenotypes conferred by the YrA resistance varied when exposed to contrasting light intensities in the post-inoculation phase. The implications of the results in international studies of host resistance to P. striiformis f. sp. tritici are discussed.     

Inheritance of genetic markers from two potato dihaploids and their respective parent cultivars

Summary In the first inbred generation (I₁) of cv. Black 4495 a dark green, slowly growing mutant (coded ds) was found, whereas the I₁ of its self-compatible dihaploid, B16, comprised this ds mutant and in addition the mutants virescens (v) and yellow margin (ym). The occurrence of ds and ym might trace back to diploid S. phureja, one of the ancestors of Black 4495. No lethal mutants were observed in I₁ of B16. Analysis of I₁ of cv. Gineke revealed a simplex condition for virescence and either duplex or triplex heterozygosity for one lethal gene. On the other hand, the I₁ of its dihaploid, G254, segregated for virescence and for three different lethal genes. It is shown that both in B16 and in G254 homozygosity of an S-bearing translocation causes early death of embryo and endosperm, thus preventing seed development. From this study it appeared that the three lethal genes from G254 affect germination rate of the seeds. The genotypes at 11 loci of B16 and G254 are presented.Visiting scientists from Birmingham, England and Mlochow, Poland, respectively.     

Cross-fertilization behaviour of some white flowering varieties of Vicia faba

Summary Applying a special design for maximalization of cross-fertilization and using flower colour as a marker, considerable differences in the percentage of cross-fertilization between white flowering Vicia faba varieties were observed. Part of these differences were due to differences in beginning of flowering in white and coloured varieties, part of them proves to be independent of this and, therefore appear to be characteristic for the variety. Interaction between mother and father varieties was absent.