Analysis of Phytophthora parasitica by retrotransposon-derived DNA fingerprinting

Phytophthora parasitica, being able to attack a wide variety of plants, is a very important plant pathogen in Taiwan. It has been shown that isolates of P. parasitica from tobacco, dieffenbachia, and loquat differed significantly from other isolates in morphology and pathogenicity and were recognized as “atypical” types of the fungus. In the current study, a partial sequence of the reverse transcriptase gene of a Ty1-copia retrotransposon was cloned from P. parasitica and used as the probe, designated herein as G2Ty-1, for genomic Southern hybridization analyses of P. parasitica. It was demonstrated that G2Ty-1 existed as a moderately repetitive sequence in the genome of P. parasitica. The banding pattern of G2Ty-1 was mitotically stable for at least five consecutive asexual generations. DNA fingerprint analysis of P. parasitica using G2Ty-1 as the probe demonstrated that the banding patterns of G2Ty-1 were highly polymorphic among the isolates analyzed. “Atypical” strains from tobacco, dieffenbachia, and loquat, nonetheless, displayed host-specific banding patterns. Phylogram generated by cluster analysis demonstrated that isolates from tobacco and dieffenbachia were well separated from each other and from all other isolates of P. parasitica. These results provided a genetic basis for distinguishing these isolates from others and validate the use of retrotransposon as a genetic marker to study phylogeny in Phytophthora parasitica.