Evolution in an autopolyploid group displaying predominantly bivalent pairing at meiosis: genomic similarity of diploid Vaccinium darrowi and autotetraploid V. corymbosum (Ericaceae).

The genomic relationship between V. darrowi Camp (2n = 2x = 24) and V. corymbosum L. (2n = 4x = 48) was examined using an interspecific tetraploid hybrid, US 75, and representatives of the parental species. Two features in the background of US 75 led to the prediction that it was an allopolyploid: (1) the parental species are quite distinct morphologically and geographically, and (2) the diploid genome was incorporated into US 75 via an unreduced gamete. However, US 75 recently was shown to display tetrasomic inheritance using molecular markers. In the present cytological study, US 75 was found to have a lower than expected number of multivalents for an autopolyploid, although it had a significantly higher number of quadrivalents than its autotetraploid parent, V. corymbosum. Normal chromosome distributions were observed at anaphase I and II, and pollen viability was high. Our findings suggest that little genomic divergence has developed between the Vaccinium species and that the polyploids may freely exchange genes with sympatric diploid species via unreduced gametes. This pattern of hybridization could be an important component of evolution in all autopolyploid groups, making them much more dynamic than traditionally assumed.