Multiple resistance to glyphosate, paraquat and ACCase-inhibiting herbicides in Italian ryegrass populations from California: Confirmation and mechanisms of resistance

Authors: TEHRANCHIAN, PARSA - University Of California; Nandula, Vijay; JUGULAM, MITHILA - Kansas State University; PUTTA, KARTHIK - Kansas State University; JASIENIUK, MARIE - University Of California

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2017
Publication Date: 12/8/2017
Citation: Tehranchian, P., Nandula, V.K., Jugulam, M., Putta, K., Jasieniuk, M. 2017. Multiple resistance to glyphosate, paraquat and ACCase-inhibiting herbicides in Italian ryegrass populations from California: Confirmation and mechanisms of resistance. Pest Management Science. 74:868-877.

Interpretive Summary: Glyphosate, paraquat and acetyl CoA carboxylase (ACCase)-inhibiting herbicides are widely used in California annual and perennial cropping systems. Recently, glyphosate, paraquat, ACCase and acetolactate synthase (ALS)-inhibitor resistance was confirmed in several Italian ryegrass populations in the Central Valley of California. Scientists from the Crop Production Systems Research Unit of USDA-ARS, Stoneville, MS, University of California, Davis, and Kansas State University conducted greenhouse and laboratory studies to characterize the possible mechanisms of resistance in the Italian ryegrass populations. The multiple resistant populations (MR1, MR2) are resistant to several herbicides from at least three modes of action. Glyphosate resistance in MR plants was partially due to Pro106-to-Ala and Pro106-to-Thr substitutions. EPSPS gene copy number and expression level were similar in plants from the Sus and MR populations. An Ile1781-to-Leu substitution in the ACCase gene sequence of MR plants confers high level of resistance to sethoxydim and cross-resistance to ACCase-inhibitors. The radiolabeled herbicide studies and phosphorimaging indicated that MR plants had restricted translocation of 14C-paraquat to untreated leaves compared to the Sus plants. This study shows that multiple herbicide resistance in Italian ryegrass populations in California, USA, is due to both target-site and non-target-site resistance mechanisms. This report of multiple herbicide resistance evolution emphasizes the importance of including non-chemical management strategies, such as cultural and mechanical practices, for management of Italian ryegrass and sustainable use of non-selective global herbicides such as glyphosate and paraquat.

Technical Abstract: BACKGROUND: Glyphosate, paraquat and acetyl CoA carboxylase (ACCase)-inhibiting herbicides are widely used in California annual and perennial cropping systems. Recently, glyphosate, paraquat, ACCase and acetolactate synthase (ALS)-inhibitor resistance was confirmed in several Italian ryegrass populations in the Central Valley of California. This research characterized the possible mechanisms of resistance. RESULTS: The multiple resistant populations (MR1, MR2) are resistant to several herbicides from at least three modes of action. Dose-response experiments revealed that the levels of resistance to glyphosate, sethoxydim and paraquat were ' 45, ' 122, and ' 20-fold, respectively, for the MR1 population and ' 24, ' 93, and ' 4-fold, respectively for the MR2 population. Accumulation of shikimate in the herbicide-susceptible (Sus) plants was significantly greater than in the MR plants 32 h after light pretreatments. Glyphosate resistance in MR plants was partially due to Pro106-to-Ala and Pro106-to-Thr substitutions. EPSPS gene copy number and expression level were similar in plants from the Sus and MR populations. An Ile1781-to-Leu substitution in the ACCase gene sequence of MR plants confers high level of resistance to sethoxydim and cross-resistance to ACCase-inhibitors. The radiolabeled herbicide studies andphosphorimaging indicated that MR plants had restricted translocation of 14C-paraquat to untreated leaves compared to the Sus plants. CONCLUSION: This study shows that multiple herbicide resistance in Italian ryegrass populations in California, USA, is due to both target-site and non-target-site resistance mechanisms. This report of multiple herbicide resistance evolution emphasizes the importance of including non-chemical management strategies, such as cultural and mechanical practices, for management of Italian ryegrass and sustainable use of non-selective global herbicides such as glyphosate and paraquat.