Building up resistance by recurrently exposing target plants to sublethal doses of herbicide

Abstract

Application of a series of sublethal rates of diclofop-methyl (DM) herbicide to cloned individuals of Lolium multiflorum Lam increased their level of resistance to this herbicide. Under controlled environmental and field conditions, individuals of L. multiflorum genotypes herbicide-acclimated with 35 and 70 g a.i. ha −1 diclofop-methyl rates showed up to 80% survival and produced more aboveground biomass when exposed to four times higher rates compared to herbicide non-acclimated plants. The acquired increase in individual herbicide tolerance was not transmitted to their offspring, denoting the nature of acclimation response. The lack of transmission of resistant traits to the progeny highlights that exposure to sublethal rates of herbicide in susceptible individuals allowed for the expression of pre-existing cytoplasmatic information or simultaneously induced and selected extra-nuclear contents associated with resistance. The potential mechanisms through which induced tolerance may occur in L. multiflorum plants treated with sublethal concentrations of diclofop-methyl are discussed. Any recommendation or attempt to control weeds by reducing herbicide rates to increase economic returns and reduce the risk of environmental contamination should (a) acknowledge the potential acclimation responses in target plants and (b) be made and based on long-term studies.