The use of isozymes and PCR-based DNA polymorphism in aquatic weed management: a case-study on introduced and native clones of a hybrid complex

Enzyme polymorphisms have been widely used in aquatic plants since the 1980 s. Studies on DNA polymorphisms are less numerous and a case-study using bo th methods on Scirpus is worked out. Along the unique freshwater tidal zone of the River Schelde (Belgium), clumps of Scirpus species are mostly scatt ered in small and fragmented locations on the dikes and mud flats. Most of these taxa are native S. triqueter, S. tabernaemontani or intermediate morp hological forms. However, several cultivated strains of S. tabernaemontani have been introduced in recent years. Such 'exotic' strains have been plant ed to stabilize the muddy riverbanks and became well established and may pe rform better than the native hybrid complex. In order to determine the exis ting genetic diversity among these species and the possibility for genetic pollution, stems of 30 clumps from a series of locations along the tidal ri ver were investigated for seven enzymes (SDH, PGM, EST, MNR, GOT, 6PGD and ME) and for markers at DNA level using random amplified polymorphic DNA's ( RAPD) of 22 decanucleotides. Data analysis of the allozymes and of the ampl ified DNA fragments enabled us to classify unambiguously the different Scir pus taxa. Direct evidence of hybridization between S. triqueter and S. tabe rnaemontani could not be obtained, but the putative hybrids are genetically intermediate or close to S. triqueter when considering the DNA polymorphis m. The introduced clones of S. tabernaemontani consisted of at least three groups of genotypes of which one was very related to the native ones. The e scaped clumps could be assigned to a third introduced but less-related stra in.