Selection of rhizobacteria for pre-emergence control of wild poinsettia, horseweed and sourgrass

This study aimed to select rhizobacteria isolates for pre-emergence control of three glyphosate-resistant species: horseweed ( Conyza sumatrensis ), sourgrass ( Digitaria insularis ), and wild poinsettia ( Euphorbia heterophylla ). Nineteen strains of Bacillus spp. and thirty-four strains of Pseudomonas spp. were isolated from soil samples from the states of Minas Gerais, Sao Paulo, Parana, and Santa Catarina. These strains were evaluated in vitro and under greenhouse conditions for inhibition of seed germination and growth of target weeds. Several strains of Bacillus spp. and Pseudomonas spp. inhibited the germination and radicle growth of the three target species in Petri dishes containing agar-water medium with the respective bacterial isolates, separately. However, Bacillus spp. strains A1B1, A1B3, A1B4, A2B2, A2B3, A10B1, A10B5, A11B1, and A13B3 were the only ones to inhibit germination of horseweed seeds in greenhouse soil. The soil methodology (greenhouse) was more effective in the selection of strains than the in vitro methodology for not overestimating the bacterium-host interaction and for simulating better field conditions. Promising Bacillus spp. strains must be identified at the species level and cha­racterized for metabolite production, plant growth regulation, root colonization, and effect on cultivated plants.