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Leaf rust and stripe rust are devastating wheat diseases, causing significant yield losses in many regions of the world. The use of resistant varieties is the most efficient way to protect wheat crops from these diseases. Sharon goatgrass (Aegilops sharonensis or AES), which is a diploid wild relative of wheat, exhibits a high frequency of leaf and stripe rust resistance. We used the resistant AES accession TH548 and induced homoeologous recombination by the ph1b allele to obtain resistant wheat recombinant lines carrying AES chromosome segments in the genetic background of the spring wheat cultivar Galil. The gametocidal effect from AES was overcome by using an 'anti-gametocidal' wheat mutant. These recombinant lines were found resistant to highly virulent races of the leaf and stripe rust pathogens in Israel and the United States. Molecular DArT analysis of the different recombinant lines revealed different lengths of AES segments on wheat chromosome 6B, which indicates the location of both resistance genes. Key words: Aegilops sharonensis, wheat, recombinant lines, leaf rust resistance, stripe rust resistance, DArT mapping. Les rouilles brunes et jaunes sont des maladies devastatrices chez le ble puisqu'elles causent d'importantes pertes de rendement dans plusieurs regions du monde. L'emploi de varietes resistantes est le moyen le plus efficient de proteger le ble de ces maladies. L'egilope de Sharon (Aegilops sharonensis ou AES), une espece diploide sauvage apparentee au ble, presente une haute frequence de resistance aux rouilles brunes et jaunes. Les auteurs ont employe une accession resistante de l'AES, TH548, et induit de la recombinaison homeologue a l'aide de l'allele ph1b pour obtenir des lignees recombinantes de ble dotees de resistance grace a des segments chromosomiques de l'AES introduits dans le fond genetique du cultivar de ble de printemps Galil. L'effet gametocide de l'AES a ete surmonte en employant un ble mutant << anti-gametocide >>. Ces lignees recombinantes etaient resistantes a des races tres virulentes des rouilles brunes et jaunes en Israel et aux Etats-Unis. Des analyses DArT realisees sur les differentes lignees recombinantes ont revele que les segments chromosomiques de l'AES introduits sur le chromosome 6B du ble etaient de differentes longueurs, ce qui a permis de deduire l'emplacement des deux genes de resistance. [Traduit par la Redaction] Mots-cles: Aegilops sharonensis, ble, lignees recombinantes, resistance a la rouille brune, resistance a la rouille jaune, cartographie a l'aide de marqueurs DArT., Introduction Leaf rust, caused by Puccinia triticina Erikss., and stripe (yellow) rust, caused by Puccinia striiformis Westend. f. sp. tritici Erikss., are major wheat diseases. Leaf rust can cause yield [...]

Nuclear DNA amount (1C) was determined by flow cytometry in the autotetraploid cytotype of Hordeum bulbosum, in the cytologically diploidized autotetraploid cytotypes of Elymus elongatus, Hordeum murinum subsp. murinum and Hordeum murinum subsp. leporinum, in Hordeum marinum subsp. gussoneanum, in their progenitor diploid cytotypes, and in a newly synthesized autotetraploid line of E. elongatus. Several lines collected from different regions of the distribution area of every taxon, each represented by a number of plants, were analyzed in each taxon. The intracytotype variation in nuclear DNA amount of every diploid and autotetraploid cytotype was very small, indicating that no significant changes have occurred in DNA amount either after speciation or after autopolyploid formation. The autotetraploid cytotypes of H. bulbosum and the cytologically diploidized H. marinum subsp. gussoneanum had the expected additive amount of their diploid cytotypes. On the other hand, the cytologically diploidized autotetraploid cytotypes of E. elongatus and H. murinum subsp. murinum and H. murinum subsp. leporinum had considerably less nuclear DNA (10%-23%) than the expected additive value. Also, the newly synthesized autotetraploid line of E. elongatus showed similar reduction in DNA as its natural counterpart, indicating that the reduction in genome size occurred in the natural cytotype during autopolyploidization. It is suggested that the diploid-like meiotic behavior of these cytologically dipolidized autotetraploids is caused by the instantaneous elimination of a large number of DNA sequences, different sequences from different homologous pairs, leading to differentiation of the constituent genomes. The eliminated sequences are likely to include those that participate in homologous recognition and initiation of meiotic pairing. A gene system determining exclusive bivalent pairing by utilizing the differentiation between the two groups of homologues has been presumably superimposed on the DNA reduction process. Key words: autopolyploidy, DNA content, DNA sequence elimination, genome size. Le contenu en ADN nucleaire (1C) a ete determine par cytometrie en flux chez les cytotypes suivants : le cyto-type autotetraploide de l'Hordeum bulbosum, les cytotypes autotetraploides diploidises (formant principalement des bivalents) de l'Elymus elongatus, des Hordeum murimum subsp. murinum et Hordeum murimum subsp. leporinum, des Hordeum marinum subsp. gussoneanum, les cytotypes diploides des especes progenitrices et d'un E. elongatus autotetraploide nouvellement synthetise. Plusieurs lignees provenant des differentes regions de l'aire de distribution de ces taxons, chacune representee par plusieurs plantes, ont ete analysees pour chaque taxon. La variation pour le contenu en ADN nucleaire au sein d'un cytotype etait tres faible chez tous les cytotypes diploides et autotetraploides, indiquant qu'aucun changement important n'etait survenu apres la speciation ou la formation d'un autopolyploide. Les cytotypes autotetraploides de l'H. bulbosum et de l'H. marinum subsp. gussoneanum diploidise presentaient la quantite attendue suite a l'addition des cytotypes diploides. Par contre, les cytotypes diploidises de PE. elongatus et des H. murinum subsp. murinum et H. murium subsp. leporinum avaient un contenu en ADN nucleaire nettement moins grand (de 10% a 23% moins) que la somme attendue. De plus, la lignee autotetraploide nouvellement synthetisee de FE. elongatus a affiche une reduction semblable a celle observee chez son pendant naturel ce qui indique que la reduction de la taille du genome serait survenue lors de l'autopolyploidisation chez le cytotype naturel. Les auteurs suggerent que le comportement meiotique de type diploide chez les autotetraploides diploidises est cause par une elimination instantanee d'un grand nombre de sequences, diverses sequences chez differentes paires de chromosomes homologues, menant ainsi a la differenciation des genomes constitutifs. Il est probable que l'on compte parmi les sequences eliminees celles qui participent a la reconnaissance des homologues a l'initiation de l'appariement meiotique. Un systeme genetique entrainant un appariement exclusivement sous forme de bivalents moyennant la differenciation des deux groupes d'homologues se seraient vraisemblablement superposee au processus de reduction de la taille du genome. Mots-cles : autopolyploidie, contenu en ADN, elimination de sequences d'ADN, taille du genome. [Traduit par la Redaction], Introduction Polyploidy, the presence of three or more chromosome sets in an organism, has played a major role in the evolution of multicellular plants (Stebbins 1950, 1971; Grant 1971; Masterson [...]

Abstract: Recent molecular studies in the genera Aegilops and Triticum showed that allopolyploidization (interspecific or intergeneric hybridization followed by chromosome doubling) generated rapid elimination of low-copy or high-copy, noncoding and [...]

Abstract: One of the intriguing issues concerning the dynamics of plant genomes is the occurrence of intraspecific variation in nuclear DNA amount. The aim of this work was to assess [...]