Abstract
Betula ovalifolia Rupr. (Betulaceae) is a dwarf birch broadly distributed in northeast Asia, but in Japan limited to two mires in Hokkaido where it is endangered because of drying habitats due to open ditches. Moreover, putative hybrids between B. ovalifolia and a congener grow along the ditches, suggesting the risk of genetic pollution and extirpation of B. ovalifolia. We aimed to elucidate the parental species of the hybrids, to develop species-specific PCR primers to cost-effectively identify hybrids without DNA sequencing, and to examine using the primers whether hybrids invade the mires. Sequencing of nrDNA ITS revealed that the parental species were B. ovalifolia and the allopatric B. ermanii, not B. platyphylla, which inhabited the same ditches. The developed primers successfully amplified the DNA of the parental species and the hybrids with a low enough error rate to screen the hybrids. PCR using the primers indicated that six of eight putative individuals were hybrids while the other two were atypically tall individuals of B. ovalifolia. Exfoliating twig bark was a diagnostic characteristic of the hybrids. Tests for hybrids using the primers showed no evidence of hybrids inside the mires. The hybrids have the same parents as the endangered Hokkaido endemic, B. apoiensis, but the hybrids in the ditches are the consequence of human disturbance and are thus considered to have no conservation value.
