نخستین گزارش از Phytopythium megacarpum در باغات پسته ایران

Phytopythium, as a new genus, has morphological characteristics between Pythium and Phytophthora genera. The members of the clade containing species of this genus have intermediate characteristics of two above-mentioned genera: i.e. globes to ovoid sporangia, as well as internal proliferations which are similar to Phytophthora species and zoospore formation and differentiation within vesicles, which resemble Pythium species. During sampling from pistachio plantations in Kerman Province, Iran in 2014-2015, Oomycete isolates were isolated from infested soil and infected roots and crowns of the pistachio tree. Morphological, morphometric and physiological characteristics of all isolates were studied. Sequencing was performed for molecular studies, on nuclear (internal transcribed spacers of rDNA, and β-tubulin) as well as mitochondrial regions (cytochrome c oxidase subunit 1) using tree primer sets: ITS4 and ITS6, COXF4N and COXR4N and Btub_F1 and Btub_R1. Phylogenetic analysis of these three regions based on neighbor-joining and maximum-likelihood methods showed a distinct clade from Pythium and Phytophthora species. Further studies led to grouping of this clade with other species of Phytopythium and identification of Phytopythium megacarpum. This species along with Php. boreale, as the closest sister group, were clustered in clade 1 of the three known clades in the phylogenetic tree of this genus species. Phytopythium megacarpum was formerly considered as one of the Pythium species and was new to the Oomycete mycobiota of Iran. This species was also reported for the first time in the world from pistachio plantations.