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The blast disease of rice caused by the fungus Pyricularia oryzae is considered one of the most important fungal diseases of rice. Currently, this disease causes damage and reduces yield every year due to the cultivation of sensitive local varieties and the specific microclimatic conditions in some of our country's fields, especially in Mazandaran and Giulan, where conditions are favorable for the disease's development. Given the significance of this disease, extensive efforts have been made to identify the factors influencing its spread and management, and several chemical fungicides have been registered and introduced for its control. Due to the environmental pollution caused by the use of chemical fungicides, as well as the potential for resistance development, one of the most economical and effective strategies for managing this disease is the introduction and cultivation of resistant varieties. In this study, the resistance of 34 promising lines from the Rice Research Institute of Iran was evaluated against the blast disease, along with two control varieties (susceptible and resistant). To assess leaf blast, in early July, the seeds of each line were separately planted in rows 50 centimeters long and spaced 10 centimeters apart in a blast nursery containing soft, nutrient-rich soil. To infect the selected lines, infected leaves from various locations in Giulan province were collected and spread over the nursery. Simultaneously, a suspension of the fungus spores was prepared at a ratio of 105 spores per milliliter and sprayed as a solution. For better infection and to maintain humidity, irrigation was carried out in a rain-like manner. The severity of the disease was assessed based on the standard international method with ratings from zero to nine. To evaluate panicle blast, seedlings were grown in large pots in the greenhouse and inoculation was done by injection method at the neck of the panicle. Finally, the disease severity was evaluated based on the international standard method with grades from 0 to 9. Nine and tow Lines showed resistance reaction to leaf blast disease with grades 1 and 2, respectively. Other lines were relatively susceptible, susceptible to highly susceptible to the disease. Three, one, and eight Lines showed resistance reaction to panicle blast disease with grades 0, 1, and 3, respectively. The remaining lines were relatively susceptible, susceptible, and highly susceptible to panicle blast disease.
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