جداسازی باکتری‌های تثبیت‌کننده نیتروژن از ریزوسفر پیاز با توانایی کنترل فوزاریوم آن

Nitrogen, as an essential element for plant growth and development, exists in the Earth's atmosphere in the form of nitrogen gas (N2). Plants are not able to directly use the nitrogen present in the atmosphere. Microorganisms in the rhizosphere perform the process of nitrogen fixation. Biological nitrogen fixation (BNF) is a process through which a group of microorganisms known as diazotrophs convert non-absorbable atmospheric nitrogen into ammonia. The resulting ammonia fixation is a nutrient that is essential for plant growth. In this research, 28 bacterial isolates were isolated from the rhizosphere and roots of onion plants samples from the area near Shahid Madani University. Laboratory tests showed that these bacteria can grow in nitrogen-free environments and have the ability to fix nitrogen. Bromothymol blue color change test was used to confirm the nitrogen fixation ability of these isolates. This test is based on the pH increase and indicator color change in the culture medium, which depends on the concentration of ammonium ions (nitrogen fixation product). The results showed that 10 isolates out of 28 bacterial isolates have the ability to fix nitrogen more than others. Greenhouse experiments showed that bacterial isolates with the ability to fix nitrogen significantly improve the growth indicators of onion seedlings, including shoot length, root length, and plant chlorophyll. The results showed that onion plants treated with nitrogen-fixing bacteria grow significantly better than control plants. Also, the test to evaluate the antagonistic activity of isolated bacterial isolates against these two fungal species, Fusarium proliferatum and Fusarium falciforme, as agents of root rot disease and according to the onion plant, in Laboratory showed that a large number of bacterial isolates have the ability to inhibit the growth of these two fungi. The top 10 bacterial isolates identified as strong nitrogen fixers in the previous steps showed 33-80% inhibition against F. proliferatum and 20-80% inhibition against F. falciforme. This research showed that the microorganisms in the soil can play a key role in supplying nitrogen needed by plants, promoting their growth and protecting them against fungal diseases. Using these microorganisms as an alternative to chemical fertilizers and pesticides can be a sustainable and environmentally friendly way to increase agricultural productivity and product health.