DETECTION OF PHYTOPHTHORA SPECIES BY OLIGONUCLEOTIDE HYBRIDIZATION TO AMPLIFIED RIBOSOMAL DNA SPACERS

Four probes were developed to distinguish DNA from isolates of Phytophthora capsici, P. cinnamomi, P. megakarya, and P. palmivora. These four probes complement different ribosomal DNA (rDNA) internal transcribed spacer (ITS) sequences that exhibit variations between species but not within species, based on previous comparative DNA-sequence analyses of 18 P. cinnamomi, two P. palmivora, two P. megakarya, and two P. capsici isolates (21). A fifth probe that was complementary to identical sequences in all Phytophthora isolates tested, a ''genus Phytophthora'' probe, was developed. DNA-DNA hybridization of the probes to ITS amplified by polymerase chain reaction (PCR) from 30 isolates representing seven Phytophthora species and from 12 isolates representing nine other genera of the Oomycete class demonstrated the utility of this approach. Probes of P. capsici, P. cinnamomi, P. megakarya, and P. palmivora hybridized only to their respective targets: three isolates of P. capsici, 18 isolates of P. cinnamomi, one isolate of P. megakarya, and two isolates of P. palmivora. In addition, the ''genus Phytophthora'' probe hybridized to the target DNA of all 30 isolates of Phytophthora species tested but not to DNA of isolates from nine other Oomycete genera.