| چکیده انگلیسی مقاله |
Extended Abstract
Background: Soybean (Glycine max L.) holds a crucial position as one of the most significant and strategic agricultural products globally. This plant serves a vital purpose in fulfilling human nutritional demands by providing vegetable proteins and edible oils, while also finding extensive use across multiple industries. However, soybean production consistently faces considerable challenges. One of the most serious threats to soybean yields is charcoal rot disease, caused by the fungus Macrophomina phaseolina. Losses attributed to this disease can be substantial; in certain instances, the disease has been known to reduce soybean yields by as much as 50%. Managing this disease has involved various strategies, including the implementation of optimal cultivation techniques, seed treatment with fungicides, and the application of biological control methods. However, the results obtained have usually been limited or short-term and have failed to permanently solve the problem. Therefore, one of the essential and key strategies for effectively managing charcoal rot disease is focusing on strengthening the genetic resistance of the host. This strategy not only provides an opportunity to reduce economic losses but also ensures the sustainability of soybean production. This research has been designed and implemented with the overall objective of identifying resistant soybean cultivars, analyzing the key mechanisms of plant resistance, and evaluating the enzymatic activity associated with this resistance.
Methods: Initially, soybean plants showing symptoms of charcoal rot were collected from different fields in Mazandaran Province. The fungal pathogen was then isolated, purified, and identified using both molecular and morphological methods. In the subsequent phase of the study, six commercial soybean cultivars were selected, cultivated, and evaluated to identify resistant and susceptible varieties. Once the seedlings reached the six-leaf stage, they were inoculated with the fungus, and two weeks later, the severity of pathogenicity was assessed. The selected resistant and susceptible cultivars were re-planted and treated with a suspension of M. phaseolina fungal spores at the six-leaf stage. Sampling was conducted at various time points post-inoculation (0, 24, 48, 72, 96, and 144 hours). Plant extracts were then prepared, and the activities of the enzymes catalase, peroxidase, and ascorbate peroxidase were evaluated.
Results: Based on the characteristics of fungal and molecular clones (ITS4/5), the causative isolate was identified as M. phaseolina. Screening results among six soybean cultivars revealed that cultivar JK exhibited the lowest level of contamination, while cultivar Sahar demonstrated the highest level of contamination. Consequently, these cultivars were identified as the most resistant and the most sensitive, respectively. The analysis of variance revealed significant differences in the activity levels of the CAT, POX, and APX enzymes across all sources. The analysis of catalase enzyme activity showed that in JK and Sahar cultivars, after fungal contamination, the activity level of this enzyme increased gradually in time intervals of 24, 48 and 72 hours after contamination. However, the amount of catalase activity at the peak time in the resistant cultivar JK was about 1.63 times higher than the sensitive cultivar Sahar at the same time. The activity of peroxidase enzyme also increased in response to fungal contamination in both studied cultivars, namely JK and Sahar. The peak activity of peroxidase enzyme was observed in the resistant cultivar JK at 96 hours after infection, which was 5.47 times the activity compared to zero time. On the other hand, the sensitive cultivar Sahar showed its highest activity level at 144 hours after contamination, which is 2.85 times the initial level recorded at zero time. Regarding the ascorbate peroxidase enzyme in the resistant cultivar JK, the activity of this enzyme increased continuously for 72 hours after being infected with the fungus and then went through a decreasing process. The highest level of enzyme activity in cultivar JK was measured at 72 hours, which was approximately 2.38 times the control level. In the sensitive cultivar Sahar, the activity of this enzyme increased gradually after infection and reached its maximum level at 144 hours after infection, showing an increase of 1.47 times the initial amount recorded at zero time.
Conclusion: The results indicate differences in the performance of antioxidant enzymes between resistant and susceptible cultivars, reflecting varying plant responses to stress caused by the pathogenic fungus. Based on the analyses and findings, the JK cultivar, which exhibits higher activity of enzymes such as catalase, ascorbate peroxidase, and peroxidase, has demonstrated superior performance compared to other soybean genotypes under conditions of charcoal rot disease. This suggests a greater tolerance of the JK cultivar to the disease. Since no cultivars have been identified as completely resistant to this disease so far, it is possible to identify genotypes that excel in this area by evaluating the activity levels of their enzyme systems and defense mechanisms against the disease. These genotypes can then be recommended as tolerant cultivars for cultivation in infected areas.
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