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A TC/AG-repeat microsatellite sequence derived from the rice blast fungus (Magnaporthe grisea) hybridized to all of the centromeres of Hordeum vulgare chromosomes, but hybridized faintly or not at all to the chromosomes of Hordeum bulbosum. Using this H. vulgare centromere-specific probe, the chromosomes of four F[sub 1] hybrids between H. vulgare and H. bulbosum were analyzed. The chromosome constitution in the root tips of the hybrids was mosaic, i.e., 7 (7v, H. vulgare) and 14 (7v + 7b H. bulbosum), or 14 (7v + 7b) and 27 (14v + 13b), or 7 (7v), 14 (7v + 7b), and 27 (14v + 13b). The 27-chromosome tetraploid hybrid cells were revealed to have the NOR (nucleolus organizer region) bearing chromosome of H. bulbosum in a hemizygous state, which might indicate some role for this chromosome in the chromosome instability of the hybrid condition. The chromosomal distribution showed that the chromosomes of H. vulgare were concentric and chromosomes of H. bulbosum were peripheral in the mitotic squash. This non-random chromosome distribution and the centromere-specific repeated DNA differences in the two species were discussed in relation to H. bulbosum chromosome elimination. Meiotic chromosome analyses revealed a high frequency of homoeologous chromosome pairing in early prophase. However, this chromosome pairing did not persist until later meiotic stages and many univalents and chromosome fragments resulted. These were revealed to be H. bulbosum by fluorescence in situ hybridization (FISH) analysis with the H. vulgare centromere-specific probe. Because the chromosome segregation of H. vulgare and H. bulbosum chromosomes at anaphase I of meiosis was random, the possibility for obtaining chromosome substitution lines in diploid barley from the diploid hybrid was discussed.Key words: Hordeum vulgare, Hordeum bulbosum, centromere-specific repeated DNA, FISH, chromosome instability.Un microsatellite TC/AG dérivé du Magnaporthe grisea, l'agent de la pyriculariose du riz, s'hybride à tous les centromères des chromosomes du Hordeum vulgare, mais n'hybridait que faiblement ou pas du tout aux chromosomes du Hordeum bulbosum. À l'aide de la sonde spécifique des centromères du H. vulgare, les chromosomes de quatre hybrides entre l'H. vulgare et l'H. bulbosum ont été analysés. Le complément chromosomique au niveau des pointes racinaires était mixte : 7 (7v, H. vulgare) et 14 (7v + 7b H. bulbosum) ou 14 (7v + 7b) et 27 (14v + 13b), ou encore 7 (7v), 14 (7v + 7b) et 27 (14v + 13b). Les cellules hybrides tétraploïdes à 27 chromosomes se sont avérées hémizygotes pour le chromosome du H. bulbosum qui porte l'organisateur nucléolaire (NOR). Cela pourrait suggérer un rôle pour ce chromosome dans l'instabilité chromosomique liée à la condition hybride. La distribution chromosomique a révélé que les chromosomes du H. vulgare sont concentriques alors que les chromosomes du H. bulbosum sont localisés en périphérie des étalements mitotiques. Cette distribution chromosomique non-aléatoire et les différences entre les deux espèces au niveau de l'ADN répétitif spécifique au centromère sont discutées par rapport à l'élimination d'un chromosome du H. bulbosum. L'analyse de chromosomes méiotiques a révélé une haute fréquence d'appariements homéologues tôt en prophase. Cependant, cet appariement chromosomique ne persistait pas lors des stades méiotiques ultérieurs et plusieurs univalents et fragments chromosomiques étaient observés. Ceux-ci se sont avérés provenir du H. bulbosum sur la base d'une analyse d'hybridation in situ en fluorescence (FISH) à l'aide d'une sonde spécifique des centromères du H. vulgare. Comme la ségrégation des chromosomes du H. vulgare et du H. bulbosum était aléatoire lors de l'anaphase I de la méiose, les auteurs discutent des perspectives d'obtention de lignées de substitution d'orge diploïde à partir de l'hybride diploïde.Mots clés : Hordeum vulgare, Hordeum bulbosum, ADN répétitif spécifique au centromère, FISH, instabilité chromosomique.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

The PI 386148 triticale from Russia is among the highest resistant line to the Russian wheat aphid (RWA) (Diuraphis noxia (Mordvilko)). This triticale line was used as the male parent in crosses with Lamar wheat (Triticum aestivum L.). The F1 plants were backcrossed to Lamar wheat. The progenies were tested for RWA biotype 1 reaction for at least eight backcross and selfing generations. Five lines from these selections were identified for their resistance to the RWA and their seeds were increased for agronomic and other characterizations. Molecular and cytological analyses of these lines were performed using genomic in situ hybridization and rye chromosome-specific microsatellites markers. Three lines were cytologically stable and carried a pair of rye (Secale strictum (C. Presl) C. Presl) chromosomes as disomic addition lines of 1R. One line was unstable and showed a moderate level of mixoploidy with monosomic additions of 1R. Duplication of rye chromosome 1R was also identified. No wheat-rye chromosome interchange was detected, suggesting little homology between S. strictum and T. aestivum chromosomes. Specific microsatellite primers were used to identify the rye chromosomes present in each line. One rye chromosome, 1R, from the donor species contains genes for RWA resistance. Grain yield and test weight of three of the lines were similar to some adapted released wheat varieties under stress conditions.

In situ hybridization with [3H]dCTP labelled pScT7 (5S rDNA) and pTa80 (18S + 26S rDNA) indicated that both hybridized to the terminal regions of two pairs of chromosomes in Triticum monococcum. When the hybridization was performed with a mixture of both probes, only two pairs of chromosome arms were labelled, which suggested that the loci of both genes were located in juxtaposition to one another. Both probes labelled one pair of sites more heavily than the other. Southern analysis of 5S with BamHI-digested DNA from 12 accessions of T. monococcum (including T. urartu) produced two superimposed ladders of approximate sizes of 500 and 330 bp, which differ from T. aestivum in which 500- and 420-bp ladders were found. The 500-bp ladder is derived from chromosome 5A (5SDna-A2) and the 330-bp ladder from chromosome 1A (5SDna-A1). The recognition site for SstI was present in the long spacer region but absent in the short spacer as in T. aestivum; however, unlike T. aestivum, there were HaeIII (GGCC) and HindIII (AAGCTT) recognition sites in the short spacer region. The TaqI recognition sites (TCGA) in the long and short spacer regions are probably more highly methylated in T. monococcum than in T. aestivum. The results have implications regarding the evolutionary changes that occurred in the A genome of the hexaploid compared with the diploid.