Theplant pathogenic Phytophthora drechsleri is morphologically similar to some other non-papillate Phytophthora spp., especially P. melonis, and it is difficult to discriminate these convergent taxa. It seems that the Iranian putative P. drechsleri isolates from different cucurbit species have been generally misidentified and their characteristics do not match with P. drechsleri. In order to compare these two groups, authentic P. drechsleri isolates and isolates from different cucurbits were assessed for morphological, physiological (cultural, temperature relations, mating type), and molecular traits. Multiple gene genealogy analysis were performed on regions of nuclear (ITS, β-tubulin, translation elongation factor 1α, elicitin) and mitochondrial (cytochrome c oxidase subunit I) gene sequences. Congruence was observed in different phylogenetic data sets. The present study demonstrated that putative P. drechsleri isolates from cucurbits and pistachio trees were a distinct species and belonged to P. melonis. Data showed that P. melonis was a homogenous species and there were no considerable molecular intraspecific variations between isolates from cucurbits and isolates from other hosts. Design of a molecular species-specific identification tool for P. melonis isolates is under investigation. 

Keywords: Internal transcribed spacer of rDNA, Phylogeny, Phytophthora melonis, Oomycota

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