Effect of glyphosate on the physiological parameters of horseweed

Abstract

The aim of this study was to determine changes in the photosynthetic process and the inhibition of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPs) by shikimic acid accumulation, after application of the herbicide glyphosate in four biotypes of C. sumatrensis collected in the state of Rio Grande do Sul. Therefore, the experiments were conducted under greenhouse and laboratory, assessing plant biomass, photosynthesis rate, transpiration and water use efficiency; the amount of shikimic acid was calculated for each treatment. Glyphosate application reduced growth and affected the photosynthesis rate and water use efficiency of the biotypes differentially, and the resistant biotype had small interference from glyphosate, while physiological parameters of the susceptible biotype were deeply affected by the herbicide. Susceptible biotypes had higher shikimic acid accumulation than the resistant biotype, indicating differential sensitivity of EPSPs to glyphosate between resistant and sensitive biotypes.