Evidence of sexuality in European Rubus (Rosaceae) species based on AFLP and allozyme analysis

Reproduction of polyploid Rubus species is described as facultatively apomi ctic. Pollination is needed for seed set, but most seedlings are produced a sexually by pseudogamy. Although sexual processes may occur, clonal diversi ty can be extremely low. We performed a pollination experiment to investiga te the breeding system and used allozyme and AFLP markers to analyze geneti c variation among and within seed families in R. armeniacus and R. bifrons. Pollination either with self or outcross pollen was necessary to trigger s eed set. Outbreeding marginally increased the number and quality of seeds c ompared with selfing. The enzyme PGI revealed some genetic variation within seed families. Seven other enzyme systems were monomorphic. The more detai led AFLP analyses with five primer pairs detected the same rate of genetic variation (14-17% of seedlings were generically distinct) and confirmed the allozyme results for the same individuals. No genetic variation was found between the seed families from within a species collected in widely separat ed populations, but clear species-specific differences were observed. The r esults support the view that polyploid Rubus species are pseudogamous apomi cts with low genetic diversity among and within seed families. However, sex ual reproduction occasionally occurs and contributes to the maintenance of genetic variation within natural populations.