Ali Akbar Safari Sinegani

PGPB play an important role in agricultural systems, and contain broad range of bacterial genera. Therefore, in this study, seeds of wheat were inoculated with 18 rhizobacteria strains belonging to Azotobacter chroococcum (14SPI, 44SP-2, 16SP-2, 14SP2-1), Pseudomonas sp. (24A-1, 34A-2, 34SPIII, 35SP-2), Agrobacterium sp. (14A-4, 22SP-1), Rhizobium sp. (12A-3), Sphingomonas sp. (37SP), Stenotrophomonas sp. (16SP7-2), Citrobacter sp. (44 A-4S), Achromobacter sp. (14SPIII), Klebsiella oxytoca (4A-1), Beijerinckia sp. (2SP-5) and 36 A-2L isolate, to determine the effects on growth and yield of spring wheat under greenhouse condition. In this study, 18 carrier-based PGPB treatments along with one negative (B0: no inoculation) and two positive controls (B0N50 and B0N100; containing 50% and 100% of urea fertilizer, respectively) were used. The results showed that inoculation treatments had no significant effect on some plant parameters (e.g., chlorophyll index, spike length) compared with the B0, but revealed significant differences (p < .01) in other parameters such as seed weight, seed number, total dry weight, and N uptake of grain. B0N100, B0N50, and 14A-4 significantly enhanced the total dry weight (shoot, root, spike, and leave) by 35%, 32.4%, and 28.5% as compared to the control, respectively. These trends were observed in seed number and seed weight, too. Highest content of grain N uptake and Zn uptake were in 14SPI, content of P was in 44SP-2, and K and Fe content were achieved in 16SP-2 and 14SPI. In general, Agrobacterium sp. 14A-4, A. chroococcum (14SP-I, 16SP-2, and 44SP-2) were effective isolates to improve qualitative and quantitative traits of wheat.

This study aimed to compare the prevalence of antibiotic-resistant coliforms and Escherichia coli strains between industrial and antimicrobial-free poultry manure. The mean counts of high-level antibiotic-resistant coliforms were determined using the spread plate technique. Metal and antibiotic resistance of Escherichia coli strains in manure samples was compared using plate dilution and CLSI procedures, respectively. Several multi-drug resistant Escherichia coli strains were screened for plasmids using alkaline lysis method as well. The relative abundance of high-level antibiotic-resistant coliforms was significantly (p < 0.05 and 0.001) higher in industrial manure than in antimicrobial-free manure. Metal analysis indicated that the concentrations of copper (Cu), zinc (Zn), lead (Pb), and cadmium (Cd) in manure samples were significantly (p < 0.05) correlated with the percentage of coliforms resistant to several antibiotics. The number of multidrug-resistant Escherichia coli strains was significantly (p < 0.001) higher in industrial manure (97.4%) than in antimicrobial-free manure (80.7%). Four out of twelve screened Escherichia coli strains harbored plasmids. Considering the high number of drug-resistant isolates in both samples, reductions in co-selecting agents is essential for the effectiveness of antibiotics, along with controlling the activities which cause the spread of resistance.