Herbaceous host plants diversity and phylogenetic relationship among isolates of Phytophthora parsiana

The high temperature-tolerant oomycete Phytophthora parsiana was considered to be limited to woody plants. In the preliminary study, the host range of the pathogen on annual herbaceous plant species using six isolates of P. parsiana including type strains from different sources was examined under greenhouse conditions. Among herbaceous species including cucurbits, pepper, pulse and oil crops, two isolates were pathogenic to pepper. Then three cultivars of pepper were used to discriminate pepper cultivars to sixteen isolates of P. parsiana. Results showed P. parsiana were pathogenic to red pepper (‘Anheim’ and ‘Casabel’cultivars) but not bell pepper. This is the first report of an herbaceous host of P. parsiana (sensu lato). Phylogenetic relationships of the pathogenic isolates of P. parsiana from pistachio to pepper and two isolates of the species from pistachio from Rafsanjan and Yazd were not pathogenic to pepper were examined. Based on sequences of the internal transcribed spacer (ITS) region of the ribosomal RNA, isolates pathogenic to pepper and one from Rafsanjan were in a group of P. parsiana belonging to clade 10 but the Yazd isolate had no genetic similarity to P. parsiana, being placed in clade 6 of the ITS tree, closely matching that of Phytophthora taxon Walnut (99-100 nucleotide identity). This is the first report of Phytophthora taxon Walnut from pistachio in Iran.