Relationships Among Group IV Phytophthora Species Inferred by Restriction Analysis of the ITS2 Region

The polymerase chain reaction (PCR) was used to amplify the ITS2 region of nuclear ribosomal DNA from six Phytophthora species which comprise taxonomic Group IV. Digestion of the ca. 600 bp PCR product with restriction enzymes Alu I, Dra I, Hha I, Hinf I, Msp I, and Taq I revealed variation which allowed relationships among the species to be assessed. P. infestans, P. mirabilis and P. phaseoli were indistinguishable from one another with all enzymes tested. With Alu I and Taq I. P. ilicis, P. colocasiae. and P. hibernalis each showed unique banding patterns different from the common banding pattern shared by P. infestans. P. mirabilis. and P. hibernalis. Dra I allowed differentiation of P. ilicis and P. colocasiae from P. infestans, P. mirabilis, P. phaseoli, and P. hibernalis. all of which shared a common banding pattern. Hha I allowed differentiation of P. colocasiae and P. hibernalis from P. infestans, P. mirabilis, P. phaseoli, and P. ilicis. Hinf I allowed differentiation of P. ilicis and P. hibernalis, (each of which showed a unique banding pattern) from P. infestans, P. mirabilis, P. phaseoli, and P. colocasiae. Msp I allowed differentiation of P. hibernalis from the other five species. Species groupings determined by restriction analysis of ITS2 were consistent with those based on morphological criteria. These results show that restriction analysis of PCR‐amplified TS2 regions can be useful as an adjunct to morphological criteria in Phytophthora species identification.