Evaluation of Bacteria from Soil and Rhizosphere as Herbicidal Candidates of Some Broadleaf Weeds

T HE USE of bacteria in biological weed control is an alternative ecofriendly way to tackle weed problems and reduce the risk of herbicide resistance.In this study, we obtained four main active bacterial isolates under the genera Pseudomonas, Bacillus and Xanthomonas from Wadi El Natroun region.All the tested bacterial isolates caused high significant reductions in seed germination and seedling growth of Convolvulus arvensis and Portulaca oleracea.Bioassaying ethyl acetate crude extracts of these isolates showed that Pseudomonas sp.(isolate 1) was the most active against seedling stage of Portulaca oleracea.The cultural filtrate of the same isolate caused 100% reduction when assayed on seed germination, shoot and root length of Convolvulus arvensis and Portulaca oleracea.At the highest concentration (40mg/ml) of the crude ethyl acetate extract, the reduction percentage in total biomass fresh weights of Portulaca oleracea and Convolvulus arvensis seedlings reached 71.27 and 39.37%, respectively.The EC 50 values (concentration that inhibited growth by 50%) were 1.3 and 1.64mg/ml for Portulaca oleracea and Convolvulus arvensis, respectively.Comparative 16S rRNA gene sequencing analysis and biochemical characterization demonstrated that isolate FS15 was member of the genus Pseudomonas and belongs to the Pseudomonas aeruginosa group with Pseudomonas aeruginosa strain NR 113599.1 as the closest relative (99.5% sequence similarity).In conclusion, Pseudomonas aeruginosa has high potential to be developed as natural bacterial herbicide and may be used in broadleaf weed control.