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

Abstract

This is the first report of low-dose glyphosate selection causing a shift towards paraquat resistance. Herbicide resistance in weed species is a serious threat to world agriculture. We report rapid resistance evolution in the genetically variable cross-pollinated grass weed Lolium rigidum when recurrently selected with low doses. Results show that an herbicide-susceptible L. rigidum population selected over three generations with below-label doses of glyphosate exhibited not only glyphosate resistance evolution but also a progressive and concomitant shift in sensitivity to the structurally unrelated herbicide paraquat. Thus, reduced paraquat sensitivity was a consequence of recurrent selection with glyphosate at low doses. In the three-time glyphosate-selected progeny, the estimated paraquat dose to cause 50% mortality (LD 50 ) was 4-fold greater than for the unselected susceptible parent. Studying the evolutionary outcomes of below-label herbicide dose selection can help prevent genetic changes in weed populations and sustain the efficacy of herbicides widely used in world agriculture.

Understanding the potential for resistance evolution to the new herbicide pyroxasulfone: field selection at high doses versus recurrent selection at low doses

“…3; Table 4). The evolution of pyroxasulfone resistance, evidenced here by low‐dose pyroxasulfone selection, is similar to other examples of rapid resistance evolution experimentally observed in L. rigidum (Neve & Powles, 2005a,b; Busi & Powles, 2009, 2011; Manalil et al. , 2011).…”

“…Studies with Lolium rigidum (Gaud.) have shown that recurrent low‐dose herbicide selection can lead to rapid and substantial herbicide resistance evolution (Neve & Powles, 2005a; Busi & Powles, 2009, 2011; Manalil et al. , 2011).…”

Response to low-dose herbicide selection in self-pollinatedAvena fatua

“…Studies with the highly genetically variable, cross‐pollinated and resistance‐prone grass weed species Lolium rigidum (Gaud.) have established that recurrent selection at low herbicide dose can rapidly lead to herbicide resistance evolution . Obligate cross‐pollination in L. rigidum ensures that with low‐dose herbicide selection the genetic traits conferring survival will be shared through cross‐pollination, and herbicide resistance will evolve .…”

Occurrence and distribution of glyphosate-resistant giant ragweed (Ambrosia trifida L.) in southwestern Ontario

“…and rigid ryegrass (Lolium rigidum Gaud.) are known for their genetic diversity and biotypes with resistance to several different herbicide modes of action have been reported (Falk et al 2005;Nordby et al 2007;Stachler and Loux 2007;Norsworthy et al 2008;Busi and Powles 2011;Heap 2011). The repeated use of glyphosate in an intensive GR cropping system has led to the selection of several GR weed biotypes worldwide (Heap 2011).…”