Abstract
The relation between host reaction and yield losses due to net blotch disease was tested in six commercial barley cultivars through two seasons 2017/18 and 2018/19 under field infection compared with same six cultivars protected with fungicide (Montero). Net blotch incidence was also recorded as disease severity % and area under disease progress curve (AUDPC). Yield losses were parallel to net blotch severity and area under disease progress curve in both seasons. Net blotch triggered losses irrespective of the level of resistance obsessed by the cultivars. Giza134 and 135 showed lowest levels of severity% and AUDPC followed by Giza 124 and 125 which exhibited lower levels of losses as compared to the highly susceptible cultivar Giza 2000 and 121 in which grain reduction reached 8.71% to 11.32% and 5.53% to 8.83% respectively. Contrariwise, losses in yield per plot in Giza134 and 135 ranged from 2.80 % to 5.00% and 3.05% to 5.03% respectively, compared to Giza 2000 and 121 ranged from 26.70% to 29.11% and 19.58% to 22.89% respectively. The cultivars Giza 2000 and 121 had great values for susceptibility while, the average grain yield potential for both cultivars were less than others as Giza 134 and 135. This indicated that Giza 2000 and 121 have low tolerance level. Phonotypical scoring of disease with yield losses were resistance cultivars (Giza 134 and 135), moderately resistance (Giza 124 and 125) and Giza 2000 and 121 were also identified as susceptibility to net blotch at natural infection. This is an important study to prove that Giza 134 and Giza 135 barley cultivars are resistant under natural infection compared to treated cultivars with Montero. This study is very important to the plant breeders to protect the resistant cultivars from breakdown and create new resistant cultivars, consequently decreasing the fungicides use and environmental pollution.