شناسایی باکتری اندوفیت Bacillus velezensis جداشده از بذر گندم به عنوان عامل مهارزیستی و محرک رشد گیاه

Fusarium head blight (FHB), Fusarium crown rot (FCR), and bacterial leaf streak (BLS) have been identified as destructive wheat diseases worldwide. The lack of resistant cultivars and the harmful effects of using chemical pesticides to control these diseases have encouraged researchers to use biological agents as an environmentally friendly strategy. Plants carry a small community of microbes that affect their growth and protect them against pathogens. This study aimed to isolate and identify antagonistic plant growth-promoting endophytic bacteria in wheat seeds. In this research, 51 endophytic bacteria were isolated from the seeds of 14 Iranian wheat cultivars (Arg, Bahar, Baharan, Behrang, Chamran, Chamran 2, Dena, Falat, Heidari, Parsi, Pishgam, Sayonz, Sirvan and Sivand). According to the calculations, the logarithm of endophytic bacterial population density in seeds was estimated from 0.602 (Chamran 2) to 1.544 (Parsi). The isolates were evaluated against two important pathogens Fusarium graminearum and Xanthomonas translucens by dual culture assays. Three isolates showed antagonistic activity against both phytopathogens. Among these bacteria, one potent antagonist isolate, capable of increasing seed germination by 15.85% more than untreated seeds and also could increase the growth of roots and shoots in vitro, was selected for further investigation. This isolate could produce protease, pectinase, cellulase, amylase, catalase, indoleacetic acid (IAA), ammonia, siderophore, and solubilized phosphate, but could not produce lipase, chitinase, and hydrogen cyanide (HCN). Growing on a minimal salt medium DF test showed that this isolate could produce ACC deaminase, and growing on a nitrogen-free medium showed that it has the potential to fix atmospheric nitrogen. Greenhouse experiments indicated that plant growth-promoting characteristics of shoots and roots in endophyte-treated wheat seedlings increased and included length (33.22 and 38.83%, respectively), fresh weight (43.08 and 39.88%, respectively) and dry weight (63.07 and 61.5%, respectively). One thousand grains weight also increased by 11.29% in treated plants. The plant protection rate against pathogenic bacterium was 64.23%. The percentage of FHB infection reduction was 80.33% and FCR disease severity reduction was 78.19%. By whole genome sequencing (WGS), the bacterial isolate was identified as Bacillus velezensis. This endophyte has a wide antagonistic range, so it can be used as a biocontrol agent to protect plants against various phytopathogens and as a fertilizer to increase the growth of different plants. The effect of this endophytic bacterium on the biocontrol of fusarium crown rot and bacterial leaf streak diseases was reported for the first time.