Genomic and genetic relationships among species of Leymus (Poaceae: Triticeae) inferred from 18S-26S ribosomal genes

The 18S-26S ribosomal genes in three closely related species of Leymus (Poaceae: Triticeae) were examined using fluorescence in situ hybridization (FISH) and restriction fragment length polymorphism (RFLP). Both approaches revealed a close relationship between L. arenarius (8x = 56, northern European) and L. racemosus (4x = 28. central Eurasian), whereas L. mollis (4x = 28, northern American/Pacific) was distinct. Each species had three homologous pairs of major rDNA loci: a1, a2, and a3 for L. arenarius: mi. m2, and m3 for L. mollis: and r1, r2, and r3 for L. racemosus. Leymus arenarius had in addition three minor loci, a4, a5, and a6. The major loci of L arenarius and L, racemosus were identical, indicating that the former species could have originated from the latter; via interspecific hybridization and/or polyploidy. The rDNA-RFLPs further indicated relationships of these species to other species of Leymus (L. karellini, 8x = 56 and L. angustus, 12x = 84) and Psathyrostachys (P. fragilis, huashanica, P. juncea, and P, lanuginosa, which are all diploids). A phenogram constructed from 20 BamHI, EcoRI, and DraI rDNA fragments revealed closer relationship between the two genera, Leymus and Psathyrostachys, than that among species within a genus.