Etiology and Molecular Identification of Phytophthora spp. Causing Root Rot of Pistachio in Arid Agricultural Zones

Abstract

Root rot disease caused by Phytophthora species has emerged as a significant threat to pistachio cultivation in arid agricultural zones, leading to severe reductions in plant vigor, productivity, and orchard sustainability. The present study aimed to investigate the etiology and molecular identification of Phytophthora spp. associated with root rot symptoms in pistachio plantations located in drought-prone agricultural regions. Field surveys were conducted across selected orchards exhibiting symptoms such as wilting, chlorosis, crown necrosis, and root decay. Diseased root and rhizosphere soil samples were collected and subjected to pathogen isolation using selective media techniques. Morphological characterization of isolates was performed based on colony appearance, sporangial morphology, and hyphal structures. Molecular identification was carried out through polymerase chain reaction (PCR) amplification and sequencing of the internal transcribed spacer (ITS) region of ribosomal DNA, followed by phylogenetic analysis. The results confirmed the presence of multiple Phytophthora species associated with pistachio root rot, with Phytophthora cinnamomi and Phytophthora nicotianae identified as the predominant pathogens. Pathogenicity assays demonstrated severe root tissue degradation and significant reduction in seedling growth under controlled conditions. Environmental factors such as poor drainage, saline irrigation water, and elevated soil temperatures were found to enhance disease incidence and pathogen proliferation in arid ecosystems. The study highlights the importance of integrating molecular diagnostics with traditional pathogen identification methods for accurate detection of Phytophthora species. Early diagnosis and effective disease management strategies are essential to minimize economic losses and improve the long-term sustainability of pistachio cultivation in arid agricultural environments.