بررسی کنش ضد‌قارچی جدایه‌های بومی Bacillus thuringiensis علیه قارچ عامل پژمردگی گوجه فرنگی Fusarium oxysporum f. sp. lycopersici در سطح آزمایشگاه.

Tomato (Lycopersicon esculentum Mill) is a valuable plant in agriculture and food industry. The high content of antioxidant compounds makes this plant one of the most widely used summer crops in the world. Fusarium oxysporum f. sp. lycopersici is the cause of Fusarium wilt of tomato and one of the most relevant form species that annually brings about a tremendous economic loss at tomato fields especially in Khuzestan province of Iran. Bacillus thuringiensis is known as a biocontrol agent against most plant pests and its antifungal activity has been proven against varies plant pathogen fungi. This research was performed to do a pre-screening of the native B. thuringiensis isolates (Mollasani, Khuzestan province, Iran) based on their antifungal activities under in vitro condition. The soil samples were collected from the rhizosphere of healthy tomato plant Falat-cultivar, and the isolation of the bacteria was performed by using sodium acetate. The fungus was obtained from the collection of the Department of Plant Pathology, Faculty of Agriculture, Tarbiat Modares University, Tehran, Iran. The pathogenicity test was performed using wheat-grain inoculated with pathogenic fungi at a rate of 15 g/kg on tomato plant Falat-cultivar. Three repetitions were performed for each treatment and the symptoms were assessed qualitatively. The antifungal activity of the isolates was studied on the potato dextrose agar (PDA) medium, following dual-culture approach using four replicates per treatment. The fungal radial growth inhibition percentage was determined using ImageJ software and data analysis was performed under in a Randomized Complete Design. After 40 days, the pathogenic fungus caused symptoms such as yellowing and wilting on tomato plant compared to the control treatment. Microscopic study from the vascular area of wilted plants, confirmed the presence of fungi (Hyphae, micro and macroconidia) into the vessels. 30 bacterial isolates were isolated and purified. All isolates were gram-positive and catalase-positive. Microscopic study confirmed the stretched bacilliform shape and the presence of crystalline endospores in all isolates. Nine isolates exhibited unequal antagonistic activities against the pathogenic fungus. The isolate T-Bt 25 indicated the highest antifungal effect with 20% inhibition of the pathogenic fungus radial growth compared to other isolates. After that, T-Bt 5-2 and T-Bt 11-2 were the best isolates with 15.66% and 12% inhibition, respectively. Hence, it seems that the application of the native isolates of B. thuringiensis is a suitable choice for the biological control of the pathogen in Khuzestan Province, Iran. However, further investigations in greenhouse and field are required.