Genomic origin and organization of the hybrid Poa jemtlandica (Poaceae) verified by genomic in situ hybridization and chloroplast DNA sequences

Chloroplast DNA sequencing and genomic in situ hybridization (GISH) were us ed to investigate the genomic origin and organization of the alpine grass P oa jemtlandica. Using genomic probes of P. alpina and P. flexuosa, GISH cle arly distinguished between these two putative parental genomes and thus con firmed the hybrid nature of P. jemtlandica. The chloroplast trnL intron and trnL-trnF intergenic spacer (IGS) sequence genotypes of P. flexuosa and P. jemtlandica were 100% identical but differed from those of P. alpina by a total of ten or 11 nucleotide substitutions and six indels over 866 aligned positions, identifying P. flexuosa as the maternal parent of the P. jemtla ndica population studied here and supporting a relatively recent origin of the hybrid. GISH revealed the presence of intergenomic translocations in th e hybrid genome, indicating that the two parental genomes have undergone so me rearrangements following hybridization. It is likely that some of these chromosome changes took place soon after hybridization in order to overcome the adverse interactions between the nuclear and the cytoplasmic genomes a nd to facilitate the successful establishment of the newly formed hybrid. T he presence of intergenomic chromosome changes may play an important role i n the evolution of natural hybrids and the establishment of new evolutionar y lineages. (C) 2000 Annals of Botany Company.