گزارشی از برخی نماتدهای مهم انگل گیاهی از نهالستان‌های درختان میوه در شمال استان سمنان

Semnan is the seventh largest province of Iran. The northern part of this province includes the cities of Miami, Mahdishahr, Shahroud, Damghan and Sorkheh, which are adjacent to the Alborz Mountain range and have a mountainous climate. The vegetation of these areas is in three forms: orchards(including various types of pome and stone fruit trees, pomegranates, figs, persimmons, olives, etc.), forests(including various types of fruitful and non-fruitful trees and shrubs) and nurseries. Plant parasitic nematodes are one of the most important factors causing damage to agricultural products. The most efficient management method of these pests is preventing of infection and their spread. One of the most important ways of their spreadis through infected seedlings. Nowadays, most of the newly built orchardsare created in barren lands, where their initial infestationwith devastatingplant parasitic nematodes is unlikely. If gardeners are not careful enough in preparing healthy seedlings, the infestation of the field will start by introducing infected seedlings. In order to conduct a preliminary investigation of the infestation of nurseries in the northern Semnan province, 20 soil and root samples from the rhizosphere of pome and stone fruit trees were collected and transferred to the laboratory. After extracting nematodes using usual methods, identification and determination of population density of nematodes were done. As a result, the following nematodes were identified: Helicotylenchus dihystera, Meloidogyne sp., Mesocriconema antipolitanum, M. xenoplax, Pratylenchus thornei, P. neglectus and Paratrichodorus sp. The highest population density was related to the root-knot nematode (species identification is under investigation) with 3500 second-stage juveniles, followed by the stubby root nematode with 280individualsper 200cm3of soil. Symptoms of weakness, yellowness and low growth of seedlings were observed in the parts with high population density of nematodes. The remarkable finding relates to discovery of high populations of stubby root nematode, especially in association with pome fruit trees from different nurseries, along with symptoms of weakness and yellowness. In addition to direct damage, these nematodes can also transmit some plant pathogenic viruses. According to the obtained results, monitoring of the nurseries to assess their infestation with plant parasitic nematodes and the infection of the rootstocks with plant pathogenic viruses is highly recommended.