بررسی علل زوال درختان ارس در ارتفاعات طارم استان زنجان

The mountainous region of Tarom has some areas covered with Juneperus excelsa. Declining trees were visited between 2016 and 2020, following reports of the death of juniper trees in Tarom heights. Preliminary studies have shown a high sever infection of juniper trees by semi-parasitic plant called juniper dwarf mistletoe (Arceuthobium oxycedri (DC.) M. Bieb). At the same time, the suspicious diebacks and the canker symptoms on the branches and discoloration of the leaves highlighted the possible role of fungal pathogens in this mortality. Therefore, while surveying in the field and recording the symptoms of decaying trees, samples were taken from the foliage and roots of declining trees and transferred to the laboratory. Isolation and identification of the fungal pathogens were performed using common laboratory methods. Specimens of pests and harmful insects active on juniper trees were also collected and identified. Morphological identification of isolated fungi was performed using valid mycological keys and to confirm the identification of obtained fungal isolates, molecular methods were used by proliferation and comparison of nuclear ribosomal Internal Transcribed Spacer (ITS) region using general primers (ITS- 1 and ITS-4). In this study, more than 200 different fungal isolates were obtained, including Nigrospora oryzae fungi (31 isolates), Penicillium spp. (9 Separation), Aspergillus spp. (4 isolates), Trichoderma spp. (5 isolates), Aureobasidium pullulans (33 isolates) and Polyporus sp. (3 isolates), Phoma sp. (14 isolates), Phoma medicaginesis (3 isolates), Alternaria alternata (5 isolates), Alternaria sp. (9 isolates), Alternaria consortialis (6 isolates), Hormonema carpetanum (5 isolates), Hormonema sp. (9 isolates), Peyronellaea pinodella (4 isolates), Kabatiella microsticta (3 isolates), Microsphaeropsis spp. (8 isolates) had the highest frequency among the obtained isolates. The isolated fungi mainly belonged to opportunistic fungal pathogens which are often active on stressed hosts. Field observations showed that 100% of declined juniper trees infected with juniper dwarf mistletoe (Arceuthobium oxycedri (DC.) M. Bieb). During the survey of diebacks, it was disclosed that 27% of cases were damage from woodboring beetle pest called ((Phloeosinus nr. Aubei (Peris, 1855) (Coleoptera, Scolytinae)) and only 3 cases of damage were related to Osphranteria coerulescens (Coleoptera: Cerambycidae). Based on the results of this research it seems that the main cause of juniper trees decline in Tarom heights is juniper dwarf mistletoe (Arceuthobium oxycedri) and isolated pathogenic fungi, pest damages and environmental stresses have been the secondary and complementary role in decline and mortality of these trees.