Haplotype variation of cpDNA in the agamic grass complex Pennisetum section Brevivalvula (Poaceae)

The Brevivalvula section of the grass polyploid complex Pennisetum shows va rious reproductive systems, apomixis being the most widespread. Haplotype v ariation of chloroplast DNA was studied in the six morphological taxa (spec ies) of this section by using RFLP analysis in 54 plants corresponding to 1 4 elementary taxa, each characterized on the basis of morphology and ploidy level. Two additional species, Pennisetum glaucum and P. purpureum, which belong to another section of the same genus, were analysed for comparison. In Brevivalvula, chloroplast DNA size was estimated to range between 130 an d 133 kb. Thirteen of 15 distinct haplotypes identified in the study were s pecific to the Brevivalvula section. They were unequally distributed among the morphotypes, the ploidy levels and sampling sites. Within the Brevivalv ula section, plants of P. setosum, which are perennial and reproduce vegeta tively or by agamospermy, possessed a single specific haplotype. This speci es differed clearly from the five other morphological species, which are kn own to be annual, to show either sexual or agamospermic reproduction and wh ich shared most of the 12 other haplotypes observed in the section, suggest ing the occurrence of multiple hybridization events between the taxa. Chlor oplast DNA variation was highly geographically structured, suggesting low s eed dispersal between sites, whereas the substantial haplotype diversity ob served in the sites may indicate that agamic reproduction is responsible fo r the maintenance of distinct genetically isolated clones. Haplotype classi fication using Wagner's parsimony suggested the occurrence of bidirectional gene flow between the diploids and the polyploids, as reported already in other related apomictic complexes.