TAXONOMIC STRUCTURE OF PHYTOPHTHORA-CRYPTOGEA AND P-DRECHSLERI BASED ON ISOZYME AND MITOCHONDRIAL-DNA ANALYSIS

Intra- and interspecific isozyme variation was evaluated for 123 isolates assigned to either Phytophthora cryptogea or P. drechsleri, and compared with that of 15 isolates of P. erythroseptica and 11 isolates of P. lateralis. Isolates of P. cryptogea and P. drechsleri were from worldwide sources and displayed a high degree of variability. The majority of these isolates were subsequently divided into ten distinct groups based on numerical analysis of 24 putative enzyme loci. None of the enzyme loci were monomorphic for all ten groups. Analysis of mitochondrial (mt) DNA restriction fragment length polymorphisms of selected isolates from each isozyme group supported the isozyme data. Differences in morphological features of the ten isozyme groups of P. crytogea and P. drechsleri were not sufficiently distinct to readily distinguish between them. Isozyme analysis of P. erythroseptica revealed that it is a uniform and distinct taxon. The isolates of P. lateralis also formed a homogeneous and discrete group. An interspecific comparison revealed that the variation among the ten isozyme groups of P. crytogea and P. drechsleri was as great as that observed among P. cinnamomi, P. cambivora, P. lateralis, P. erythroseptica and P. richardiae. The combined results of isozyme and mtDNA analysis indicate that there are at least seven distinct molecular species represented by the 123 isolates of P. cryptogea and P. drechsleri evaluated in this study.