نبذة مختصرة : Background and Objectives Wheat (Triticum aestivum L.) is one of the most important crops worldwide, responsible for a large portion of the human diet. In light of the increasing population, increased demand of 20 million tons by 2025 has been predicted by the Iranian Ministry of Agriculture. However, Fusarium graminearum and Xanthomonas translucens are among the most destructive diseases that lead to high yield loss. The present study aimed to isolate and evaluate the antagonistic plant growth-promoting endophytic bacteria in Iranian wheat cultivars. Materials and Methods In this study, endophytic bacteria were isolated from different tissues (e.g., seeds, roots, and shoots) of 14 wheat cultivars: Arg, Bahar, Baharan, Behrang, Chamran, Chamran 2, Dena, Falat, Heidari, Parsi, Pishgam, Sayonz, Sirvan, and Sivand. Bacterial strains were cultured in different media (i.e., NA, LBA, and TSA 10%). Then, their antifungal and antibacterial activity against F. graminearum and X. translucens were analyzed by dual culture assays. Moreover, the effect of isolates on seed germination was evaluated in vitro. In addition, extracellular enzyme production and plant growth-promoting properties were assessed. Furthermore, the effect of endophytes on plant growth was evaluated in greenhouse trials, and finally, the selected isolates were identified by 16S rRNA gene sequencing using two sets of universal primers (rD1, fD1, and 27F, 1492R). Results In this study, a total of 464 endophytic bacteria were isolated from wheat surface-sterilized tissues. Forty-four isolates successfully suppressed both Fusarium and Xanthomonas in vitro. The highest percentage of the fungal growth inhibition was evaluated at 86.66% (CB2), and the highest clear halo around isolates, which indicated the antibacterial activity, was 49.33% (PaR28, PiR5). Among the isolated bacteria, twelve were capable of increasing seed germination in vitro by at least 10% more than untreated seeds and could increase shoot and root length, which were selected for further characterization. The clear halos, which indicated enzyme production, were calculated as follows: protease 0.36 to 2.53, cellulase 1.03 to 1.75, pectinase 1.06 to 2.65, and amylase 0.43 to 2.1 cm. The diameter of siderophore production on CAS agar medium varied from 0.21 to 1.46 cm. Moreover, IAA was between 7.05 and 14.14 μg/mL, ammonia production varied from 0.29 to 34.49 mg/mL, and phosphate solubilization was between 6.09 and 14.95 μg/mL. Greenhouse experiments indicated that the biomass was significantly increased in plants treated with endophytes. In addition, DNA sequencing using the 16S rRNA gene showed that the isolate CB2 had 99.06% homology with B. subtilis, B. velezensis, and B. amyloliquefaciens. Plus, the isolates PaR28, SeR8, BaR15, and BR20 indicated a homology of more than 99% with P. jamilae, P. polymyxa, and P. peoriae. The sequence of the mentioned isolates has been deposited in the GenBank under accession numbers MT258405 (CB2), MT258403 (BaR15), MT258407 (SeR8), MT258404 (BR20), and MT258406 (PaR28). Discussion The present study is the first report on the endophytic population in mentioned wheat cultivars and an indication of their significance in the biocontrol of X. translucens. As isolates identified in this study have several desirable characteristics, a better-informed knowledge of them can be expected to have promising applications as biofertilizers and biopesticides. [ABSTRACT FROM AUTHOR]
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