شناسایی عوامل لکه‌برگی آلترناریایی و پراکنش آنها در باغ‌های پسته استان سمنان

Plant diseases are one of the most important factors limiting pistachio production in Iran. Alternaria leaf spot causes spots on leaves and fruits (mainly resulting in shell staining), reduces photosynthesis and the quality and quantity of the pistachio fruits mainly in orchards with high humidity. In this research, in addition to identification of the causal agents of Alternaria leaf spot, their frequency and distribution were evaluated in the pistachio orchards of Semnan province during the years 1400 to 1403. Leaf and fruit samples with and without surface disinfection with 10% sodium hypochlorite solution were cultured on APDA (2.5 ml of 25% lactic acid per liter) and petri dishes were incubated at 25°C. Fungal samples were identified based on macroscopic and microscopic characteristics and the use of ITS1/ITS4, RPB2-5F2R/RPB2-7CR and EF1-728F/EF1-986R primers. Pathogenicity test of the isolates were conducted on detached pistachio leaves cv. ahmad aghaei. For each isolate five fully expanded leaves were inoculated by 5 mm discs of 6-day old fungal colonies with and without wounding. The leaves were incubated in plastic boxes with high humidity at 25°C and after 7 days, diameter of spots was measured and scores on a 4-point rating systems. The results showed that 33, 39 and 28 isolates of A. alternata, A. tenuissima and A. arborescens were isolated from pistachio orchards in Semnan province, respectively. The frequency of A. alternata, A. tenuissima and A. arborescens isolates was 58, 56 and 57% in Damghan, 24, 28 and 25% in Shahrood and 18, 15 and 18% in Miami. Also, in each species, 69, 64 and 66% of the isolates were isolated from the leaves of pistachio trees. Although in pathogenicity test, the diameter of the spots on wounded leaves was more than unwounded leaves, but in both leaves, the diameter of the spots was more than 5 mm.