Identification of a natural allopentaploid hybrid Fragaria (Rosaceae), new to Europe

The morphological recognition of interspecific hybrids in the genus Fragaria (strawberry, Rosaceae) is difficult due to the frequent lack of clear species-specific characters. A putative hybrid Fragaria taxon from Bavaria, Germany, was characterised by its somatic chromosome number, flow cytometric measurement of total nuclear DNA amount, fertility tests, and parental identification as inferred from randomly amplified polymorphic DNA (RAPD) phenotypes. The chromosome number in young root tips was 35, and the corresponding total nuclear DNA amount as measured by mean fluorescent intensity was 504, indicating pentaploidy. Detection of species-specific RAPD bands characteristic of hexaploid F. moschata and of diploid F. vesca in the RAPD phenotype of the German plant strongly suggests an allopentaploid origin with these two species as the parents, most likely through the fusing of an unreduced diploid gamete from F. vesca with a normal gamete from F. moschata. The putative hybrid has low pollen fertility, and experimental selfing and cross-pollinations using pollen from the likely parental species failed to result in any fruit or seed set. This study supports the view that allopolyploidy via unreduced gametes is an ongoing process in the speciation of the genus Fragaria.