The transitional zone ultrastructure has morphological

differences that clearly separate the chytrids, the oomycetes and green algae or plants (Barr 1992). A comprehensive multigene phylogeny of the oomycetes is not available yet find more and the painful reconstruction of the zoospore ultrastructure remains to be done for several oomycetes genera. However, absence of hairs on the anterior flagellum has been reported on many of the basal genera whereas differences K-bodies and vesicles are found among higher orders (Beakes et al. 2011; Beakes 1987). Several important morphological structures used in taxonomic keys that are easily observable by light microscopy are known to be polyphyletic characters, e.g. ornamentation of oospores, and are of little use for phylogeny. On the other hand, phylogenies based on zoospore ultrastructure features such as the helix of the transitional zone or the base and root of the flagella remained for the most part valid following the advent of Selleckchem Etomoxir molecular phylogenies. Unfortunately, the technical complexity of doing transmission electron microscopy combined with the difficulties in obtaining the proper sections of zoospores is discouraging many to pursue this line Batimastat of work. DNA technology

The pioneers in oomycete research DNA was discovered in 1953 but it is in the 1970’s that this discovery started to be exploited in oomycete research. Green and Dick (1972) determined by CsCl gradient untracentrifugation the percent GC composition and the presence of satellite bands for various Saprolegniaceae. With the advent of recombinant DNA technology in the 1970’s it was now possible to transform an organism with DNA from another species using a range of molecular biology protocols such as DNA digestion by restriction enzymes, electrophoresis, DNA hybridization, that had all been adapted to work with minute amounts of DNA. It started to be exploited by scientists working on oomycetes in the 1980’s. The impact of the

work by Gunderson et al. (1987) and Förster et al. (1990) on the classification of the oomycete at the kingdom level Aspartate was mentioned above. Klassen et al. (1987) used differential DNA extraction with CsCl centrifugation to generate restriction maps of rDNA. Panabières et al. (1989) looked at restriction fragment length polymorphism (RFLP) of total DNA, Förster et al. (1989) and Martin and Kistler (1990) looked at RFLP of purified mitochondrial DNA to compare Phytophthora species whereas Martin (1991) characterized the circular plasmid in three Pythium spp. Goodwin et al. (1989, 1990a, b) generated species specific cloned DNA probes to detect Phytophthora species by hybridization. Hulbert et al. (1988) developed a genetic map of Bremia lectucae by RFLP whereas Judelson and Michelmore (1989, 1990) studied its gene expression and identified promoters that Judelson et al.