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 (Poa ceae: Triticeae) were examined using fluorescence in situ hybridization (FI SH) and restriction fragment length polymorphism (RFLP). Both approaches re vealed a close relationship between L. arenarius (8x = 56, northern Europea n) and L. racemosus (4x = 28. central Eurasian), whereas L. mollis (4x = 28 , northern American/Pacific) was distinct. Each species had three homologou s 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 i n 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 h ave originated from the latter; via interspecific hybridization and/or poly ploidy. The rDNA-RFLPs further indicated relationships of these species to other species of Leymus (L. karellini, 8x = 56 and L. angustus, 12x = 84) a nd 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, Le ymus and Psathyrostachys, than that among species within a genus.