RAPD profiling and isozyme analysis of New Zealand Hydrilla verticillata

Abstract

Hydrilla verticillata is an invasive submerged weed, which has been introduced and become established in a variety of freshwater habitats around the world. It was first recorded in New Zealand in 1963, and today occurs in four lakes in the Hawke’s Bay region. Isozyme analyses (six enzyme systems; MDH, PGM, PGD, GPI, AAT and IDH) were carried out on these populations to determine the level and pattern of genetic diversity in New Zealand H. verticillata. Australian and USA monoecious and dioecious H. verticillata samples were also analysed for the same six enzyme systems. Four isozymes (MDH, PGM, GPI and AAT) were polymorphic between country-samples. Isozyme banding patterns of New Zealand H. verticillata populations were compared with those of H. verticillata from other countries, both by examining published data as well as by direct analysis, to determine the likely source of H. verticillata in New Zealand. Random amplified polymorphic DNA (RAPD) reaction carried out on the same sample set using 14 random primers indicated that there was a single dominant genotype present in all four New Zealand H. verticillata populations. USA and Australian H. verticillata samples contained more than one genotype. Both analyses indicated that the New Zealand H. verticillata plants were more similar to those from Australia than to either of the USA samples. The study also indicated that New Zealand H. verticillata was probably the result of a single introduction, the most likely source being Australia, and that reproduction is solely by vegetative means.