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[Traduit par la Redaction] Introduction Allopolyploidization is an evolutionary process involved in plant speciation which occurs naturally by combining two or more different genomes into a single nucleus by inter-specific [...], Recent studies in the genera Aegilops and Triticum showed that allopolyploid formation triggers rapid genetic and epigenetic changes that lead to cytological and genetic diploidization. To better understand the consequences of cytological diploidization, chromosome pairing and seed fertility were studied in [S.sub.1], [S.sub.2], and [S.sub.3] generations of 18 newly formed allopolyploids at different ploidy levels. Results showed that bivalent pairing at first meiotic metaphase was enhanced and seed fertility was improved during each successive generation. A positive linear relationship was found between increased bivalent pairing, improved fertility, and elimination of low-copy noncoding DNA sequences. These findings support the conclusion that rapid elimination of low-copy noncoding DNA sequences from one genome of a newly formed allopolyploid, different sequences from different genomes, is an efficient way to quickly augment the divergence between homoeologous chromosomes and thus bring about cytological diploidization. This facilitates the rapid establishment of the raw allopolyploids as successful, competitive species in nature. Key words: Aegilops, allopolyploidy, bivalent pairing, chromosome-specific sequences, diploidization, Triticum, wheat. De recents travaux au sein des genres Aegilops et Triticum ont montre que la formation d'allopolyploides enclenche de rapides changements epigenetiques qui menent a une diploidisation cytologique et genetique. Afin de mieux comprendre les consequences de la diploidisation cytologique, l'appariement des chromosomes et la fecondite ont ete examines chez les generations [S.sub.1], [S.sub.2] et [S.sub.3] de 18 allopolyploides nouvellement formes et presentant des niveaux de ploidie differents. Les resultats montrent que la formation de bivalents lors de la premiere metaphase meiotique etait superieure et que la fecondite etait accrue avec chaque generation successive. Une relation lineaire positive a ete trouvee entre une formation accrue de bivalents, une fecondite amelioree et l'elimination de sequences d'ADN non-codant a faible nombre de copies. Ces observations supportent la conclusion qu'une elimination rapide des sequences d'ADN non-codant a faible nombre de copies d'un des genomes, possiblement differentes au sein de differents genomes, est un moyen efficace pour augmenter rapidement la divergence nucleotidique entre chromosomes homeologues et entrainer une diploidisation cytologique. Ceci facilite l'etablissement rapide des allopolyploides a l'etat brut en tant qu'especes competitives en nature. Mots-cles : Aegilops, allopolyploidie, formation de bivalents, sequences specifiques des chromosomes, diploidisation, Triticum, ble.