Glyphosate effect on plant rhizobacteria

Journal or Publishing Institution: Universidad Nacional de Colombia

Study: http://www.bdigital.unal.edu.co/46478/

Author(s): Duque, G., and Madelén, J.

Article Type: Study

Record ID: 578

Abstract: Results obtained from several studies suggest that the pre-seeding application of the widely used herbicide glyphosate can alter the microbial community of the rhizosphere of non-target plants, as well as soil processes mediated by microorganisms. Although this impact should be related to the response of weed plants to glyphosate application, little is known on the changes taking place in the microbial community of weed plant rhizosphere. A field and a greenhouse experiments were conducted in order to test the influence of recommended doses of glyphosate on the rhizosphere community of the weeds mustard, tansy mustard, and volunteer wheat. The greenhouse experiment determined the effect of two recommended doses of glyphosate (450 g a.i. ha-1, 1800 g a.i. ha-1) on the fungi and bacteria inhabiting the rhizosphere of the targeted volunteer wheat (Triticum aestivum L. cv. AC Lillian) and mustard plants (Brassica juncea) as revealed by plate counts conducted 24 h, 3 d and 7 d after application. Glyphosate shifted microbial community size, increasing the rhizobacterial counts in a dose-dependent manner. This effect could be direct, as glyphosate can be released by roots into the rhizosphere, or through physiological changes experienced by dying plants after glyphosate application. In the field experiment, the rhizosphere soil of wheat (Triticum aestivum L. cv. AC Lillian) and tansy mustard plants (Descurainia pinnate (Walter) Britton) growing in the pea and the wheat phases of a pea-wheat rotation system, was collected before and after glyphosate application (450 g a.i. ha-1). The microbial communities were analyzed by plate counts based on colony morphology. Bacterial morphotypes were identified based on 16S rDNA. Glyphosate triggered no detectable effects on the rhizobacterial community of tansy mustard or on fungi, but glyphosate influenced differently the rhizobacterial communities of the wheat crops grown in both, the pea and the wheat stubble environments. Glyphosate increased the abundance of the known triazine-s decomposer Arthrobacter aurescens, and decreased the abundance of potentially plant-growth-promoting Mesorhizobium loti and Variovorax paradoxus strains. It is concluded that pre-seeding applications of glyphosate may have undisclosed agronomic and environmental implications.

Keywords: Rhizosphere microbial community, Herbicide, Weeds, Rotation system, Field recommended dose, Glyphosate, Wheat

Citation: Duque, G., and Madelén, J., 2015. Glyphosate effect on plant rhizobacteria. Maestría thesis, Universidad Nacional de Colombia – Sede Medellín.