Differential translocation of paraquat in paraquat‐resistant populations of Hordeum leporinum

Abstract

Two populations of Hordeum leporinum have evolved resistance to paraquat within a small area in central Tasmania, Australia. One population (THL1) was more than 80-fold resistant to paraquat when treated in winter, compared with a susceptible population (THL4) collected nearby, whereas the other population (THL2) was only 19-fold resistant. Translocation of paraquat was examined in all three populations at warm and cool temperature regimes. Herbicide was applied to a basal section of the second leaf of plants kept in the dark and translocation measured after 16 h of dark and during a subsequent light period. Paraquat absorption into the treated leaf was uniformly high in susceptible and resistant populations, with >93% of the applied herbicide absorbed within 16 h in the dark at both tempera-tures. Translocation of paraquat out of the treated leaf was low in the dark, with <4% of the herbicide translocated to the remainder of the plant. More herbicide was translocated out of the treated leaves in susceptible plants in the dark, compared with resistant plants at both temperature regimes and more paraquat was translocated at warmer temperatures. Extensive basipetal translocation of paraquat to the rest of the plant occurred in susceptible plants following exposure of the treated plants to light. However, basipetal translocation was much reduced in resistant plants in the light and corresponded to the degree of resistance. Resistance to paraquat in H. leporinum is the result of reduced translocation of paraquat out of the treated leaves.

Reduced sensitivity to paraquat evolves under selection with low glyphosate doses in Lolium rigidum

“…1; Table 1). Temperature is a major factor affecting the plant response to paraquat (Preston et al 2005;Purba et al 1995;Yu et al 2004). Similarly here, we observed higher paraquat efficacy and greater differential sensitivity to paraquat between the unselected parental and glyphosate-selected plants grown at lower temperature ( Table 1).…”

“…Figure 3a, b, c from Busi and Powles 2009 observed shift was well beyond the expected baseline variation for herbicide sensitivity to paraquat in unselected populations of L. rigidum or other species (Yu et al 2004;Preston et al 2005;Yu et al 2007). Selection experiments repeated in time and place by conducting one experiment under controlled growth room conductions and one in field conditions showed the same evolution of glyphosate resistance and concomitant reduced paraquat sensitivity (Tables 1 and 2).…”

Procedures for Detection of Resistant Weeds Using 14C- Herbicide Absorption, Translocation, and Metabolism

“…Reduced translocation was reported as the cause of resistance to paraquat in two populations of Hordeum leporinum [7]. The inability to translocate paraquat out of the treated leaves was verified with the use of 14 C-labeled paraquat comparing the two resistant populations with a susceptible one, all from Australia.…”

HRAC Classification of Herbicides and Resistance Development

“…It was concluded that the resistance to paraquat was the result of the reduced herbicide translocation out of the treated leaves [76]. One can suppose that also in this species herbicide sequestration may have been the primary cause for the altered long-distance transport.…”