جداسازی باکتری‌های مقاوم به شوری و خشکی از ریزوسفر گیاهان و ارزیابی برخی خصوصیات محرک رشدی آن‎ها

تنش‌های محیطی مانند شوری خاک و خشکی و همچنین حاصلخیزی ضعیف خاک نقش مهمی در کاهش تولید محصولات کشاورزی دارد. هدف از این پژوهش ارزیابی تحمل باکتری‌های جدا شده از ریزوسفر گیاهان زعفران، پسته و زرشک به تنش‌های شوری و خشکی و همچنین قابلیت انحلال فسفر و تولید ایندول استیک در شرایط آزمایشگاهی بود. برای این منظور از ریزوسفر هر گیاه 10 جدایه باکتری با خصوصیات ظاهری متفاوت کلونی انتخاب و از نظر رشد در محیط کشت با سطوح شوری و خشکی (صفر، 5- و 10- بار) مختلف و توان انحلال تری کلسیم فسفات و تولید ایندول استیک اسید ارزیابی شدند. نتایج نشان داد که با افزایش شوری و غلظت پلی اتیلن گلیکول در محیط کشت، رشد باکتری‌ها کاهش یافت. باکتری‌های جدا شده از ریزوسفر گیاه زرشک توانایی بیشتری نسبت به دیگر جدایه‌ها برای رشد در سطوح شوری و خشکی بالا نشان دادند. بیشترین مقدار فسفر آزاد شده در محیط مایع برابر با 629 میکروگرم بر میلی لیتر بود که به جدایه s4 تعلق داشت. حلالیت فسفر توسط جدایه‌ها در دامنه 629-237 میکروگرم بر میلی لیتر متغیر بود. متوسط انحلال تری کلسیم فسفات در باکتری‌های جدا شده از ریزوسفر گیاهان زعفران، پسته و زرشک به‌ترتیب برابر 484، 472 و 393 میکروگرم بر میلی لیتر بود. تولید ایندول استیک اسید توسط جدایه‌ها در دامنه 18.83-3.23 میکروگرم بر میلی لیتر متغیر بود. بیشترین مقدار تولید ایندول استیک اسید مربوط به جدایه s6 (18/83 میکروگرم بر میلی لیتر) بود. بنابراین می‌توان از این جدایه‎ها برای آزمون آنها برای تهیه مایه تلقیح‌های میکروبی برای القای مقاومت به گیاه و تامین عناصر غذایی و رشد آنها در شرایط تنش استفاده کرد.

isolation of salinity and drought-tolerant bacteria from the rhizosphere of plants and evaluation of some of their growth-promoting properties

extended abs tractintroductiona large part of iran, especially the provinces located in the eas t and center, is located in arid and semi-arid regions where the annual precipitation is less than 150 mm. conse-quently, agriculture conditions in these areas are challenging. environmental s tresses such as soil salinity, drought, and poor soil fertility play significant roles in reducing agricultural production. the utilization of beneficial soil microorganisms is crucial for managing agricultural production. the objective of this s tudy was to assess the toler-ance of bacteria isolated from the rhizosphere of saffron, pis tachio, and barberry plants to salinity and drought s tresses, as well as their capacity to solubilize phosphorus and produce indole acetic acid under laboratory conditions. material and methodsto isolate plant growth-promoting bacteria, soil samples were collected from the rhizo-sphere of pis tachio, barberry, and saffron plants in various regions of south khorasan province and transported to the soil biology laboratory of the faculty of agricul-ture. subsequently, the bacteria were cultured on the growth medium, and thereafter, bacterial isolates exhibiting variations in colony shape and appearance were chosen for purification and further inves tigations. following this, 10 bacterial isolates were picked and evaluated for growth in culture media with varying salinity levels (0, 10, 20, and 40 ds/m), drought conditions (0, -5, and -10 bar), as well as for the solubili-zation of tricalcium phosphate, and the production of indole acetic acid. finally, the data underwent s tatis tical analysis using sas software, and mean comparisons were performed utilizing the lsd tes t.resultsthe results indicated that bacterial growth decreased with increasing salinity and poly-ethylene glycol concentration in the culture medium. bacteria isolated from the rhi-zosphere of barberry plants demons trated a greater ability than other isolates to thrive in high salinity and drought conditions. as per the findings, the growth of isolates at salinity levels of 0, 10, 20, and 40 ds/m ranged from 0.603 to 1.524, 0.501 to 1.343, 0.417 to 1.234, and 0.184 to 1.038, respectively. the highes t growth at salinity levels of 0, 10, 20, and 40 ds/m was observed in isolates s2, b3, b3, and b8, respectively, while the lowes t growth was noted in isolates p6, p6, p2, and s1 at these salinity levels. the average growth (light absorption) of bacteria isolated from the rhizosphere of saffron, pis tachio, and barberry plants at -5 bar water potential was 0.779, 0.850, and 1.059, respectively, and at -10 bar water potential was 0.756, 0.563, and 0.483, respectively. the highes t growth of isolates at -5 and -10 bar water potential levels was attributed to isolate b7, where-as the lowes t growth was associated with isolates p2 and s10 at these water potential levels. the highes t phosphorus release in the liquid medium was recorded at 629 μg/ml, attributed to isolate s4. the solubility of phosphorus by the isolates ranged from 237 to 629 μg/ml. the average solubility of tricalcium phosphate in bacteria isolated from the rhizosphere of saffron, pis tachio, and barberry plants was 484, 472, and 393 μg/ml, respectively. the production of indole acetic acid by the isolates varied from 18.83 to 3.23 μg/ml, with the highes t production observed in isolate s6 (18.83 μg/ml). conclusionthe decrease in rainfall in iran’s agricultural regions, the increase in salinity and drought s tresses in these areas, and the low efficiency and negative effects of chemical fertilizers on human health and the environment have made the use of beneficial microorganisms that are resis tant to environmental s tresses more necessary than ever. the results of this s tudy showed that mos t of the isolates s tudied were able to tolerate different levels of salinity and drought in laboratory conditions up to a salinity of 40 ds/m and drought s tress of -20 bar. on the other hand, mos t of the bacterial isolates isolated from the rhizosphere of saffron, pis tachio, and barberry plants had the ability to dissolve tricalcium phosphate in solid and liquid media, reduce the ph of the environment, and also produce indole acetic acid as a plant growth-s timulating hormone. therefore, these isolates can be tes ted for the preparation of microbial inoculants to induce plant resis tance and promote growth under s tressful conditions.