A revision of Phytophthora parsiana isolates based on single-strand-conformation polymorphism of ribosomal DNA

Phytophthora parsiana has been considered as a unique and important pathogen in Iranian pistachio orchards. The description of novel and closely related species to this phylogenetic taxon in Clade 9 of Phytophthora spp. phylogenetic trees, including P. hydropathica, P. hydrogena and P. virginiana, as well as extremely heterogeneous morphological, physiological and host rang of the assigned isolates, necessitates a comparative study of the isolates as a complex species. Isolates that have been assigned to this taxon during the last 25 years, along with the isolates which have been isolated in 2014-2015 were studied using single-strand-conformation polymorphism (SSCP) of ribosomal DNA. The results of the patterns showed that the isolates assigned to P. parsiana were classified into four distinct groups. Phylogenetic analysis of cytochrome C oxidase subunit I based on maximum-likelihood inference also confirmed the results and the isolates grouped in four distinct groups along with other members of the Phytophthora spp. of clade 9. Morphology and physiology characteristics and pathogenicity tests revealed some differences between these four groups. Unlike other groups, the isolate of the third group was not pathogenic to pistachio seedlings, and the same as isolates of groups one and four it was not able to grow at 40 ° C. Additionally the micrometric characteristics of sporangia were significantly different from those of other groups. The evidence from this grouping confirms the existence of a significant intra-species variation as well as the need for a revision of the initial description of this complex species.