Hybridization and Gene Flow Between Distantly Related Species of Rubus (Rosaceae): Evidence from Nuclear Ribosomal DNA Internal Transcribed Spacer Region Sequences

Abstract

Abstract Hybridization has long been considered a source of taxonomic complexity in Rubus. This study uses molecular data to examine natural hybridization between R. caesius, a facultatively agamospermous tetraploid of subgenus Rubus (blackberries) and R. idaeus, a sexual diploid of subgenus Idaeobatus (raspberries). Both species are widespread in Europe, and hybridization between them is postulated to have given rise to numerous species, including R. maximiformis and R. picticaulis. We sequenced the nuclear ribosomal DNA internal transcribed spacer (ITS) region of R. caesius, R. idaeus, five putative hybrids from Sweden, and one individual each of R. maximiformis and R. picticaulis from Germany. Rubus caesius differs from R. idaeus at 20 nucleotide sites and one insertion/deletion event. The putative hybrids exhibit nucleotide polymorphism additivity at all or most of these sites indicating that gene flow does occur naturally between R. caesius and R. idaeus. For each of five putative hybrids we analyzed...