| چکیده انگلیسی مقاله |
Extended Abstract
Introduction and Objectives: Rice (Oryza sativa L.) serves as the primary food source for over half of the world's population. The disease caused by Rhizoctonia solani has significantly impeded rice production, resulting in substantial economic losses and posing a threat to food security. Currently, the most suitable method to control this disease is the use of commercial fungicides. However, the use of fungicides results in increased costs and harm to the environment and human health. Therefore, the utilization of biocompatible chemical compounds is regarded as an innovative and effective strategy for integrated product management and combating various stressors. One such compound is potassium phosphite, which work to reduce disease by directly affecting the pathogen and indirectly stimulating the host's defense responses.
Materials and Methods: The seeds of local Tarom and Khazar cultivars were prepared and disinfected to produce identical, pathogen-free seedlings. Subsequently, the seeds were germinated and transferred to plastic pots filled with sterile soil. Finally, the pots were moved to the growth chamber. Some of the seedlings were treated with potassium phosphite, while others served as the positive control. All the plants were then infected with R. solani. Leaf tissue sampling from the treated and control seedlings was conducted at 0, 24, 48, 72, and 96 hours after infection. The leaf extract was then obtained to measure enzyme activity, including catalase, polyphenol oxidase, and superoxide dismutase. Disease severity and enzyme activity were studied in a factorial design using a completely randomized design with two cultivars, Tarom (resistant) and Khazar (susceptible), and two treatments of potassium phosphite and R. solani, each with three replications.
Results: The results of the analysis of variance showed that the effects of the treatments were significant in all sources of changes in the severity of the disease and the activity of PPO and SOD enzymes. However, the effects of the treatments were not significant in treatment number for the CAT enzyme activity, but were significant in other sources. The severity of the disease was more pronounced in the control plants compared to the plants treated with potassium phosphite, and in the sensitive variety (Khazar) compared to the resistant variety (Tarom). Additionally, in both the control and treated plants, the disease progressed more by the 10th day after infection than on the 21 st day. Enzyme activity was significant in both the resistant (Tarom) and sensitive (Khazar) varieties, as well as between the two potassium phosphite treatments in the presence of the pathogen. The highest level of enzyme activity was associated with the Tarom variety and potassium phosphite treatment in the presence of the pathogen, while the lowest level was linked to the Khazar variety and R. solani treatment. The activity of the catalase enzyme increased in both treatments and cultivars at 24 hours after infection, then gradually decreased at 48 and 72 hours. However, at 96 hours, it reached the highest level of activity compared to the initial time. The activity of the polyphenol oxidase enzyme increased in all time periods, while the activity of superoxide dismutase gradually increased, reaching its peak at 72 hours, and then decreased at 96 hours.
Conclusion: Catalase catalyzes the conversion of hydrogen peroxide into water and oxygen, protecting the plant against oxidative damage caused by pathogens. In diseased plants, the presence of potassium phosphite led to an increase in enzyme activity compared to infected control plants. This suggests that potassium phosphite enhances enzyme activity in plants to combat pathogens. Polyphenol oxidases catalyze the oxidation of phenol to quinone, creating unfavorable conditions for pathogen development. In potassium phosphite treatment, it induces resistance, leading to increased quinone production and creating a toxic environment for the pathogen. The spread of the disease has decreased compared to the treatment of R. solani. Superoxide dismutase plays a crucial role in plant physiology by serving as signals in transmission pathways and as a defense against cell damage caused by excessive oxygen production. In plants treated with potassium phosphite, the enzyme exhibited maximum activity at 72 hours. In the control plants, this peak occurred at 96 hours after contamination. This suggests that potassium phosphite has reduced oxidative stress, thereby impeding the progression of the disease and its associated symptoms. In this study, the activities of catalase, polyphenol oxidase, and superoxide dismutase enzymes were lower in the sensitive variety (Khazor) compared to the resistant variety (Tarom). This suggests that the level of reactive oxygen species was higher in the Khazor variety, leading to an increase in the spread and symptoms of the disease. R. solani induces cell death in plants by secreting enzymes and toxins. Potassium phosphite inhibits cell death by enhancing the activity of antioxidant enzymes such as catalase, polyphenol oxidase, and superoxide dismutase, thereby impeding the progression of the fungus. Therefore, potassium phosphite can be used as a biocompatible chemical compound instead of fungicides in the integrated management of the disease.
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