Evaluation of trifluralin, metribuzin and imazethapyr herbicides effects on Bradyrhizobium japonicum isolates growth

Growth of B. japonicum isolates at different concentrations of herbicide used on soybean was studied as factorial experiment arranged in a completely randomized design with three replications. Isolates B1, B6, B43 and 0, 0.125, 0.25, 0.5, 1, 2, 4, 8 and 16 folded of the recommended doses of trifluralin, metribuzin and imazethapyr herbicides were considered as factors. Isolates population trends over time and colony forming unit (CFU) data at different herbicide concentrations were fitted using the Gompertz and four parameters logistic models, respectively. Results showed that Max. B1, B6 and B43 isolates population grown in YMB at 28 C were 4.77 × 109, 4.54 × 109 and 4.43 × 109 cell/ml, respectively. In addition to, isolates population doubled during 10.76, 11.55 and 12.51 hours and reached to their mid log phase in 26.14, 25.72 and 27.20 hours after incubation at 28 C. Using four parameters dose - response logistic models revealed metribuzin> trifluralin > and imazethapyr herbicides order affecting on B. japonicum population isolates. Mean estimated EC50 values for metribuzin, trifluralin and imazethapyr herbicides were 13, 7 and 4 mg. L-1 which were 6 to 10 times more than herbicides recommended doses.