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Carrot (Daucus carota L.) chromosomes are small and poorly differentiated in size and morphology. Here we demonstrate that fluorescent in situ hybridization (FISH) signals derived from arbitrary PCR probes can be used for chromosome identification in carrot. To prepare probes, we searched for nonpolymorphic products abundantly amplified with arbitrary decamer primers in a group of accessions representing carrot genetic diversity. As a result, 13 fragments ranging in size from 517 to 1758 bp were selected, sequenced, and used as probes for fluorescent in situ hybridization. Four of these probes produced clear and reproducible hybridization signals. The sequences showed similarity to a number of carrot BAC-end sequences, indicating their repetitive character. Three of them were similar to internal portions of gypsy and copia LTR retrotransposons previously identified in plants. Hybridization signals for the four probes were observed as dotted tracks on chromosomes, differing in distribution and intensity. Generally, they were present in pericentromeric and (or) interstitial localizations on chromosome arms. The use of the four probes allowed discrimination of chromosome pairs and construction of more detailed karyotypes and idiograms of carrot. Key words: arbitrary PCR, carrot, fluorescent in situ hybridization, karyotype, repetitive DNA. Les chromosomes de la carotte (Daucus carota L.) sont petits et difficiles a distinguer sur la base de leur taille ou de leur morphologie. Les auteurs montrent ici que les signaux produits par hybridation in situ en fluorescence (FISH) a l'aide de sondes correspondant a des produits PCR arbitraires permettent d'identifier les chromosomes chez la carotte. Pour preparer des sondes, les auteurs ont employe des amorces decanucleotidiques aleatoires pour identifier des amplicons abondants et monomorphes au sein d'un groupe d'accessions representatif de la diversite genetique chez la carotte. Ainsi, 13 amplicons dont la taille variait entre 517 et 1758 pb ont ete selectionnes, sequences et employes comme sondes lors d' analyses FISH. Quatre de ces sondes ont produit des signaux clairs et reproductibles. Ces sequences presentaient de la similitude avec bon nombre de sequences terminales de clones BAC de la carotte, ce qui suggere qu' il s' agit de sequences repetees. Trois de ces sequences presentaient de l'homologie avec les portions internes de retrotransposons LTR de type gypsy et copia decrits anterieurement chez les plantes. Les signaux d'hybridation obtenus a l'aide de ces quatre sondes prenaient la forme de suites de points sur les chromosomes, mais dont la distribution et l'intensite differait. En general, ces signaux etaient presents dans les regions pericentromeriques ou internes des bras chromosomiques. L' emploi de ces quatre sondes a permis de distinguer les paires de chromosomes et de produire des caryotypes et des idiogrammes plus detailles chez la carotte. Mots-cles : PCR aleatoire, carotte, hybridation in situ en fluorescence, caryotype, ADN repete. [Traduit par la Redaction], Introduction Identification of individual chromosomes is a major difficulty in many plant species, especially those with small chromosomes. Fluorescent in situ hybridization (FISH) combines molecular information of a DNA sequence [...]

Genomic in situ hybridization (GISH) has been proved to be the most effective and accurate technique for confirmation of hybrid character. The objective of our study was to adapt and optimize a GISH protocol for identification of donor chromatin in hybrids obtained by interspecific crosses between five Rhododendron taxa (R. aureum, R. brachycarpum, R. catawbiense 'Catharine van Tol', R. catawbiense 'Nova Zembla', and R. yakushimanum 'Koichiro Wada'). Positive results were obtained only when we used mitotic chromosome spreads prepared from anthers. The best differentiation of maternal and paternal chromosomes in hybrid genomes was obtained when 50 ng of probe was applied together with blocking DNA at a concentration of 3.0 µg/µL. The results demonstrate that GISH is a practical tool for detection of alien genomes and analysis of the constitution of the chromosomes in rhododendron hybrids. Key words: GISH, interspecific hybrids, Rhododendron sp. L'hybridation genomique in situ (GISH) est reconnue comme etant la technique la plus efficace et precise pour confirmer le statut hybride. L'objectif de cette etude etait d'adapter et d'optimiser le protocole GISH pour l'identification de la chromatine etrangere au sein d'hybrides issus de croisements interspeecifiques entre cinq especes du genre Rhododendron (R. aureum, R. brachycarpum, R. catawbiense 'Catharine van Tol', R. catawbiense 'Nova Zembla' et R. yakushimanum 'Koichiro Wada'). Des resultats positifs ont ete obtenus uniquement en employant des etalements de chromosomes mitotiques provenant des antheres. La meilleure differentiation des chromosomes paternels et maternels au sein de genomes hybrides a ete obtenue lorsque 50 ng de sonde ont ete; employees avec 3,0 µg/µL d'agent bloquant. Les resultats obtenus demontrent que la technique GISH constitue un outil pratique pour la detection de genomes etrangers et l'analyse de la constitution des chromosomes chez des rhododendrons hybrides. Mots-cles: GISH, hybrides interspecifiques, Rhododendron sp. [Traduit par la Redaction], Introduction Rhododendrons are among the most popular ornamental plants in Europe and North America. The genus Rhododendron L. of the family Ericaceae comprises about 1000 wild species, and most of [...]

Karyotype analysis provides insights into genome organization at the chromosome level and into chromosome evolution. Chromosomes were marked for comparative karyotype analysis using FISH localization of rDNA genes for the first time in Apioideae species including taxa of economic importance and several wild Daucus relatives. Interestingly, Daucus species did not vary in number of rDNA loci despite variation in chromosome number (2n = 18, 20, 22, and 44) and previous publications suggesting multiple loci. All had single loci for both 5S and 18S-25S (nucleolar organizing region) rDNA, located on two different chromosome pairs. The 5S rDNA was on the short arm of a metacentric chromosome pair in D. crinitus (2n = 22) and D. glochidiatus (2n = 44) and on the long arm of a metacentric pair in other Daucus species, suggesting possible rearrangement of this chromosome. For other Apiaceae, from two (Apium graveolens), to three (Orlaya grandiflora), to four (Cuminum cyminum) chromosomes had 18S-25S rDNA sites. Variability for number and position of the 5S rDNA was also observed. FISH signals enabled us to identify 20-40% of the chromosome complement among species examined. Comparative karyotype analysis provides insights into the fundamental aspects of chromosome evolution in Daucus. Key words: Apiaceae; Daucus; rDNA genes; fluorescence in situ hybridization; karyotypes; karyotype symmetry.