Clonal diversity in the rare Calamagrostis porteri ssp. insperata (Poaceae): comparative results for allozymes and random amplified polymorphic DNA (RAPD) and intersimple sequence repeat (ISSR) markers

Four populations of the rare, highly clonal grass Calamagrostis porteri ssp . insperata were examined using allozymes and the two polymerase chain reac tion (PCR)-based markers, random amplified polymorphic DNA (RAPD) and inter simple sequence repeat (ISSR) bands. Only one of the 15 allozyme loci was v ariable and two alleles were detected, both of which were found in two popu lations, while only one genotype was detected in the other two populations. ISSR and RAPD markers detected more genotypes within populations than did allozymes. ISSR markers detected more diversity than RAPD markers in three of the four populations examined. In one population, no RAPD diversity was found whereas eight different genotypes were found among the 10 plants with ISSR markers. This diversity is present despite rare flowering, no documen ted occurrence of seed set in natural populations and very low seed set wit h experimental pollinations, all of which suggest that sexual reproduction rarely occurs. The subspecies is self-compatible, but seed initiation is lo wer in self ed ovules; also, there is high embryo abortion regardless of po llen source. Variation detected by RAPD and ISSR primers may reflect higher levels of sexual reproduction in the past, very rare sexual reproduction i n extant populations, somatic mutations, or a combination of the three. Alt hough the PCR-based markers identify several multilocus genotypes within po pulations, it is not known whether these all represent distinct genets gene rated by sexual reproduction or result from somatic mutations in the old, p erennial and highly clonal plants.