Document Type : Research paper-Persian
Authors
1
M.Sc. Graduate of Plant Pathology, Department of Plant Protection, Faculty of Agriculture, Razi University, Kermanshah, Iran
2
Department of Plant Protection, Razi University, Kermanshah
3
Associate Professor, Department of Plant Protection, Faculty of Agriculture, Razi University, Kermanshah, Iran
4
Assistant Professor, Department of Soil Science, Faculty of Agriculture, Razi University, Kermanshah, Iran
5
Associate Professor of Department of Plant Protection, Campus of Agriculture and Natural Resources, Razi University, Kermanshah, Iran
Abstract
Background and Objectives: Potato (Solanum tuberosum L.) is a vital crop of great global importance. Common scab is one of the most destructive diseases affecting the quality and yield of potatoes. Effective disease management strategies for potatoes include crop management, crop rotation, seed certification, natural and chemical pesticides, disease prediction models, germplasm screening, and the development of resistant varieties. Sulfur fertilization improves potato resistance to common scab, possibly by decreasing the soil pH. Applying sulfur and Thiobacillus bacteria in alkaline and calcareous soils has improved nutrient solubility and reduced damage caused by common potato scab disease.
Materials and Methods: An experiment was conducted to investigate the effects of sulfur and Thiobacillus on tuber yield and the common scab disease index under field conditions. The farm had a history of natural and uniform infection with potato scab disease. The treatments included: 1- control (no use of Thiobacillus and sulfur), 2- application of Thiobacillus, 3- granular sulfur, 4- liquid sulfur, 5- Thiobacillus+granular sulfur, and 6- Thiobacillus+granular sulfur+liquid sulfur. The experiment was conducted using a randomized complete block design with four replications.
Results: Analysis of variance indicated that the application of sulfur and Thiobacillus significantly affected tuber yield and the common scab disease index. However, there was no significant difference in the mean number of plants among the experimental treatments. Regarding the mean number of tubers, the count increased from 104 in the control group to 135.75 in the treatment with granular sulfur+liquid sulfur+Thiobacillus treatment. This combination significantly increased tuber weight by approximately 4 kg compared to the control. Regarding the average number of tubers per plant, the treatments of granular sulfur+liquid sulfur+Thiobacillus and granular sulfur+Thiobacillus showed a significant difference compared to the control, increasing the number of tubers by 13.06% and 8.10%, respectively. Both treatments also significantly increased the mean tuber weight per plant by 19.69% and 16.21%, respectively, compared to the control. The percentage and disease index varied under the influence of the experimental treatments. The lowest disease index on potato tubers was associated with the simultaneous application of granular sulfur+liquid sulfur+Thiobacillus, followed by liquid sulfur alone. The decrease in the disease index on potato tubers can be attributed to the reduction in pH resulting from sulfur application. This study demonstrated that the simultaneous application of sulfur and Thiobacillus can effectively lower soil pH.
Discussion: In conclusion, the application of sulfur and Thiobacillus bacteria enhances the yield and quality of potato tubers by improving soil conditions and plant nutrition. The forms of sulfur used played a crucial role in disease management; liquid sulfur, either alone or in combination with other treatments, significantly reduced disease severity. Liquid sulfur contains sulfate forms and has a pH of approximately one. Additionally, its liquid form allows for better penetration into soil pores and does not require soil microbial processes to alter pH. In contrast, powdered and granular forms of sulfur must be converted to sulfate forms by sulfur-oxidizing bacteria such as Thiobacillus. This conversion process is lengthy and gradually reduces soil pH over time. In the present study, various forms of sulfur, especially the liquid form, effectively reduced soil pH, although it did not lower it enough to classify the soil as acidic. It is important to note that the study's soil was calcareous, which has buffering properties that prevent drastic pH changes. Moreover, the effect of sulfur is not solely dependent on pH; even low amounts or specific forms of sulfur can significantly reduce common potato scabs without altering soil pH. This phenomenon may be due to the conversion of sulfur into toxic forms for microbes, such as hydrogen sulfide (H2S).
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