LrGSTU181 Contributes to Glufosinate Resistance in the Multiple Resistant Lolium rigidum Populations

Glufosinate is increasingly applied alongside glyphosate to control glyphosate-resistant weeds, a practice that has led to emerging resistance issues. Here, glufosinate resistance was confirmed in two multiple-resistant Lolium rigidum (glyphosate, ALS- and ACCase inhibitors) populations, NLR70 and WALR70 (RIs of 4.47 and 2.17, respectively), with no target-site GS resistance mutations. GST and P450 inhibitor studies identified distinct mechanisms: NBD-Cl reversed glufosinate resistance in both populations, while malathion reversed resistance only in population NLR70. Resistance in population NLR70 involved both the overexpression of LrGS1-2 and LrGS2 and the upregulation of LrGSTU181, CYP94B3, and possibly other GSTs and P450s. Whereas in population WALR70, resistance likely involved LrGSTU181 and possibly other GSTs. Transgenic validation demonstrated that LrGSTU181 contributes to glufosinate resistance and clodinafop-propargyl. These findings suggest a possible preadaptation scenario wherein detoxification genes selected under long-term herbicide pressure contribute to the evolution of resistance to chemically distinct herbicides.