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Genome Analysis of the Tetraploid Pseudoroegneri tauri¹

The alloploid nature of some tetraploid accessions of Pseudoroegneria tauri (Boiss. & Bal.) A. Löve and P. spicata (Pursh) A. Löve was investigated by conducting meiotic analyses of the following hybrids: P. tauri (2n=28) x P. libanotica (Hackel) D.R. Dewey (2n=14, genomes SS); P. tauri x P. spicata (2n=14, genomes SS); P. tauri x P. spicata (allo-4x, 2n=28, genomes SSXX); P. tauri x Agropyron cristatum (L.) Gaertn. (2n=14, genomes PP); and P. tauri x A. cristatum (2n=28, genomes PPPP). Meiotic data of these hybrids showed that P. tauri possessed both the S and P genomes, and it had only the S genome in common with the allotetraploid P. spicata. Mitotic cells showed 14 short and 14 long chromosomes in P. tauri; 14 short and 7 long chromosomes in P. tauri x P. libanotica; and 14 long and 7 short chromosomes in P. tauri x A. cristatum. It is concluded that two tetraploid accessions of P. tauri from Iran used in this study have the PPSS genome formula in which the long chromosomes are those of the P genome and the short ones are those of the S genome. An unknown (X) genome present in allotetraploid P. spicata differs from both the S and the P genomes, and possibly is an H genome. This study revealed that the alloploid nature of P. tauri, and possibly some tetraploid P. spicata accessions, is not due to the presence of a Ph-like genetic system because of the high frequencies of nonhomologous pairing or incomplete preferentiality observed in these triploid and tetraploid hybrids. In view of these findings, forage grass breeders should not use these amphiploids in crosses with autotetraploid species in the genus Pseudoroegneria. Taxonomists must find a way to classify the natural amphiploid species with PPSS genomes.

Key Words: Crested wheatgrass • Bluebunch wheatgrass • Genome • Meiotic analyses

² Research geneticists and botanist, respectively, USDA-ARS, Forage and Range Research, Utah State Univ., UMC-63, Logan, UT 84322-6300.

Received for publication October 15, 1985.