THE GENOME ORIGIN OF TETRAPLOID SPECIES OF LEYMUS (POACEAE, TRITICEAE) INFERRED FROM VARIATION IN REPEATED NUCLEOTIDE-SEQUENCES

To investigate the origin of the tetraploid species of Leymus Hochst., we examined variation in 26 repeated nucleotide sequence families isolated from four species of Triticeae. The genome relationships were determined by calculating repeated nucleotide sequence identity (RSI) between species. RSI is the ratio of the number of diagnostic bands (DBs) and diagnostic hybridization intensities (DIs) in Southern blots of a diploid taxon encountered in a polyploid species divided by the total number of the DBs and DIs of the diploid taxon (DB is a band in Southern blot observed in a single diploid taxon, and DI is the intensity of hybridization higher by at least one order of magnitude in a diploid taxon than in any other diploid taxon). The RSIs of Psathyrostachys Nevski with Leymus ranged from 0.92 to 0.95, which confirmed that the N genome of Psathyrostachys was involved in the phylogeny of Leymus. Since RSIs of other genera of Triticeae with Leymus varied from 0.00 to 0.17, it is unlikely that any of them contributed the second pair of Leymus genomes. RSIs were also calculated between Leymus and the lineage of Lophopyrum Love-Thinopyrum Love or the lineage of Lophopyrum-Thinopyrum-Pseudoroegneria (Nevski) Love-Agropyron Gaertn. The RSIs were close to zero, which made it unlikely that the second pair of Leymus genomes originated from even an extinct species in these major lineages of Triticeae. Several lines of evidence were obtained that indicated that the second pair of Leymus genomes is also from Psathyrostachys. The genomes of tetraploid species of Leymus were designated N1N1N2N2, rather than JJNN as proposed by other workers.