ارزیابی میزان انتقال بیماری لکه نواری جو به نسل بعد در مزرعه

Barley leaf stripe disease caused by Pyrenophora graminea Ito & Kuribayashi with the anamorph Drechslera graminea (Rabeneh. Ex. Schlech. Shoem) is one of the most important seed-borne diseases in the barely-growing areas of the world. This research aims to detect the level of infection to fungus P. graminea in seed samples, evaluate the pathogenicity of isolates isolated, and investigate the transmission rate of Barley leaf stripe disease by seeds infected. In order to identify the disease-causing fungus, samples were taken from barely seed fields of Isfahan, Tehran, Alborz, Khuzestan, North Khorasan, South Khorasan and Hamedan provinces according to the International Rules for Seed Testing (ISTA). For isolation of fungi, 100 seeds of each sample, after washing with water and surface sterilization with 1% sodium hypochlorite solution and were placed on different agar media with alternating 12 hours light and 12 hours darkness at 22 ± 1 °C. Purification of fungal colonies was performed using single spore and hyphal tip methods on 2% water agar medium. The fungal isolates were identified based on morphological characteristics and valid identification keys and used to confirm species identification from molecular method based on ITS-rDNA regions were amplified by ITS1 and ITS4 primers and a partial sequence of the β-tubulin gene. Pathogenicity test of isolates and the transmission rate of disease to the next generation were carried out using susceptible "Reihan" cultivar in a randomized complete block design with four replications. Seed were inoculated by sandwich technique according to Houston and Oswald and disease severity was assessed by Mathur and Bhatnagar method. Based on the morphological characteristics, differences in the mycelium growth and color were noticed among isolates collected from different regions. In general, eight isolates belonging to P. graminea were identified and isolated in seed samples. According to the results, the highest percentage of natural infected with fungus P. graminea in seed samples of barley were belong to the samples collected from Tehran (four isolates), Hamedan (three isolates), and Khuzestan (one isolate) provinces, respectively. No infection was observed in the seed samples collected from Alborz, Isfahan, North Khorasan and South Khorasan provinces. The results of pathogenicity test showed that all fungal isolates on barley seedlings were pathogenic and weakly pathogenic. The results showed that the rate of disease transmission in the field by seeds infected with P. graminea was on average about 23%. In general, the level of seed infection is within the national standard of barley seed health in the field. Therefore, it is necessary to use of certified seed and disinfection of seeds before planting using recommended fungicides to prevent the transmission of fungal pathogen and spread of the disease.