Repetitive DNA Polymorphism Analysis as a Tool for IdentifyingPhytophthoraSpecies

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Abstract
A method has been developed for the rapid extraction of the total DNA of Phytophthora. Up to 100 .mu.g of DNA, with a size greater than 23 kb, could be recovered from 0.25 g of frozen mycelium. The DNA was digested with a restriction enzyme, then subjected to electrophoresis in 1% agarose gels. After staining with ethidium bromide, the gels were examined under UV light. Repetitive DNA fragments appeared as numerous discrete bands over a faint smear. The method was applied to 39 isolates belonging to 12 species of Phytophthora [P. cactorum, P. palmiuora, P. megakarya, P. parasitica, P. capsici, P. citrophthora P. infestans, P. megasperma, P. cambivora, P. cinnamomi, P. cryptogea, and P. drechsleri]. Isolates belonging to a single species exhibited the same digestion pattern, whereas different species had clearly different patterns. This held true when different restriction enzymes were used, except the minor intraspecific variations were occasionally detected with methylation-sensitive enzymes. The analysis of repetitive DNA profiles discriminated between the very similar species P. cryptogea and P. drechsleri. It also supported the heterogeneous status of P. megasperma by differentiating the soybean isolates. In contrast, complete homogeneity was observed among profiles from 12 isolates of P. parasitica, including eight isolates from tobacco. It is suggested that, because of its simplicity, the method might be useful, not only in investigating taxonomical problems, but also for identification purposes.