الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The field investigations were carried out in the Experimental Farm of Faculty of Agriculture, Kafrelsheikh University, Egypt during the two successive growing seasons of 2014/2015 and 2015/2016. The laboratory investigations were carried out in the plant pathology and biotechnology lab and EPCRS Excellence Center. Evaluation the efficiency of ten treatments against the natural infection with net blotch on the susceptible barley Giza 2000 was studied. Effect of treatments against Drechslera teres which caused barley net blotch disease and untreated control on barley were investigated. The best disease control effect was achieved with belize fungicide treatment, which gave a highly significantly reduced disease symptoms in both seasons compared with seed treatment by premis or non-fungicide treatments. BTH treatment it gave a medium effect on disease severity. Tannic acid treatment showed slight a little difference compared to control treatment. The increased levels of ROS early after infection could play a pivotal role in killing the fungus or inhibiting the severity of disease symptoms as well as immunizing plants by increasing enzyme activities. Interestingly enough that the treatments were efficient so that the field characters values were increased significantly compared with control treatment. It seems that early accumulation of H2O2 and O2.- could have a dual roles, first role is inhibiting or killing the pathogens early, second immunization of plants by stimulating the activities of antioxidant enzymes later on which thereby, neutralize the harmful effect of ROS and consequently suppressing disease symptoms, decreasing the electrolyte leakage and increasing chlorophyll a and b concentrations and yield as well. It can be recommends to give more attention to these new mechanisms of resistance particularly in relation to early accumulation of ROS levels and antioxidant activities which are very important for plant breeders and useful for finding alternative control strategies as well. These new and interesting promising results could help the plant breeders to create new resistant barley cultivars as well as decreasing environmental pollution from fungicides use, in addition to producing organic food safe for human health.