نقش تغذیۀ گوگرد و مایه‌زنی با باکتری تیوباسیلوس در مهار بیماری پاخوره گندم ناشی از Gaeumannomyces Tritici

بیماری پاخوره با عامل gaeumannomyces tritici، یکی از مخرب‌ترین بیماری‌های ریشۀ گندم در سراسر جهان است. از این رو ارائه راهکاری مدیریتی جهت کنترل این بیماری، بسیار ضروری به نظر می‌رسد. هدف از این پژوهش بررسی نقش تغذیه با گوگرد و اثر باکتری تیوباسیلوس بر وقوع بیماری پاخوره گندم بود. بدین منظور، ابتدا خصوصیات فیزیکیشیمیایی خاک مورد آزمون ارزیابی شد. گوگرد در غلظت‌های صفر، دو، چهار و هشت گرم بر کیلوگرم با خاک مخلوط شد و به سه صورت مورد مصرف قرار گرفت. در یک تیمار، خاک غنی‌شده با غلظت‌های مختلف گوگرد بلافاصله با بیمارگر مایه‌زنی و مورد کشت گندم قرار گرفت، در تیمار دوم خاک غنی‌شده با غلظت‌های مختلف گوگرد به مدت دو ماه در گلخانه نگه‌داری شد و سپس مایه‌زنی و کشت شد. در تیمار سوم نیز خاک غنی‌شده با غلظت‌های مختلف گوگرد با باکتری تیوباسیلوس تیمار شد و بلافاصله مایه‌زنی و کشت انجام شد. تجزیۀ خاک مورد آزمایش نشان داد این خاک آهکی بوده و ph آن 24/7 یعنی نسبتاً قلیایی است. میزان دسترسی نیتروژن و عنصر روی آن مناسب بود، ولی غلظت عناصر آهن، مس و تا حدودی فسفر خاک کم بود. نتایج نشان داد که غلظت‌های مختلف گوگرد به صورت کشت بلافاصله و نگه‌داری دو ماهه اثر معنی‌داری در کاهش بیماری پاخوره نداشتند، اما در تیمار همزمان گوگرد و باکتری تیوباسیلوس در غلظت هشت گرم بر کیلوگرم خاک شدت بیماری حدود 45 درصد کاهش یافت. تیمار خاک با گوگرد در غلظت دو گرم بر کیلوگرم خاک با و بدون نگه‌داری دو ماهه وزن خشک گیاه را به ترتیب 20 و 25 درصد افزایش داد ولی افزایش بیشتر غلظت اثری بر افزایش رشد گیاه نداشت. در تیمار گوگرد و باکتری تیوباسیلوس با افزایش غلظت گوگرد، وزن خشک گیاه 25 درصد افزایش داشت. در مجموع، ترکیب گوگرد و باکتری تیوباسیلوس می‌تواند به عنوان رهیافتی امیدبخش در مهار پاخوره و بهبود رشد گندم مدنظر قرار گیرد.

Effect of Sulfur Nutrition and Thiobacillus Inoculation on Suppression of Take-all Disease Caused by Gaeumannomyces tritici

Introduction: Wheat takeall caused by Gaeumannomyces tritici fungus is one of the most destructive diseases in the world. The disease is common in alkaline to natural, nonfertile and lowdrainage soils. Thereby, wheat takeall can be suppressed by reducing soil pH. In recent years, sulfatecontaining fertilizers had been substituted with new sulfurfree fertilizers which decrease soil content of sulfur and sulfuroxidizing bacteria, significantly. So, soil amendment with mineral sulfur or Thiobacillus spp. could be reconsidered to reduce soil pH. However, soil amendment with mineral sulfur seems to be more effective when the rhizosphere is colonized by sulfuroxidizing bacteria. This study aimed was to investigate the effect of mineral sulfur and Thiobacillus sp. on takeall disease and wheat growth.;Materials and Methods: Physicochemical properties of soil were analyzed based on standard methods. Sulfur was mixed with soil in 0, 2, 4 and 8 g/kg of soil with three methods. In the first method, sulfur amended soil was inoculated with the pathogen and sown immediately. In the second method, amended soil was incubated for two months then inoculated and seeded with wheat. In the third method, sulfur amended soil was inoculated with Thiobacillus sp. bacteria and sown immediately. G. tritici inoculum was prepared on oat seeds and was placed in a layer under plant seeds. Disease severity was checked once plants seedling in control pots exhibited the disease symptoms. The experiments were carried out in a completely randomized design with four replicates. Analysis of variance was done by SAS 9.1. ;Results and Discussion: Analysis of soil showed the examined soil was calcareous and moderately alkaline. It has appropriate nitrogen and zinc content but slightly Fe, Cu and P are deficient. Results exhibited that sulfur amended has no significant role on takeall disease neither with incubation nor without incubation. However, mixed treatment with sulfur and Thiobacillus sp. decreased disease severity in concentration depended on manner. The highest disease suppression achieved in 8 g /kg sulfur of soil which decreased disease severity up to 45%. Soil amendment with 2 g/kg sulfur of soil either incubated or not increased plant dry weight 20 and 25%, respectively. However, a further increase in sulfur concentration showed no more increase in plant growth. In a combination with sulfur and Thiobacillus sp., wheat aerial parts dry weight was increased paralleled with an increase in sulfur concentration and reach to 25% higher than control in 8 g /kg sulfur of soil. Calcareous soils are highly buffered and it is very difficult to change their pH. In our experiment, the Soil amendment with mineral sulfur was unable to reduce pH as much as necessary for Takeall suppression. However, sulfur had synergistic interaction with Thiobacillus sp.. Indeed, these bacteria can colonize the plant rhizosphere efficiently. Thereby, they can reduce the pH of the rhizosphere zone instead of whole balk soil. In this situation, G. tritici could not survive in an acidic condition of the rhizosphere. On the other hand, mineral sulfur improved plant growth in all concentrations. It should be considered that sulfur could be uptake by the plant as a nutrient element. However, sulfuroxidizing bacteria will help the plant to uptake sulfur more efficiently. It should be considered that Thiobacillus is compatible with other biocontrol bacteria such as Bacillus and Pseudomonas. These bacteria are highly effective in Takeall disease but cannot survive well in calcareous soils. Coinoculation of these bacteria with Thiobacillus sp. in the presence of sulfur seems to be a promising approach in biological control of Takeall disease.;Conclusion: Our results showed that a combination of sulfur with sulfuroxidizing bacteria could be a promising approach in the suppression of Takeall in wheat. In recent years, integrated disease management and integrated crop management receive high attention in susceptible agriculture. In these strategies, agricultural practices such as plant nutrition are considered as multifaceted practice. This means that soil amended with specific fertilizer not only increases plant growth but it can increase or decrease specific plant disease. In the case of sulfur, this element not only decreases Takeall disease but also improves the availability of other nutrients such as Fe, Zn and Cu. Furthermore, it should be considered that soil amendment with a low amount of sulfur is not effective to reduce soil pH in buffered calcareous soils and we need to add sulfuroxidizing bacteria to improve fertilizer efficiency. This combination is effective against Takeall disease.