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Understanding cross- and multiple-herbicide resistance in Setaria adhaerens from olive orchards with two decades of multiple herbicides use.

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Title: Understanding cross- and multiple-herbicide resistance in Setaria adhaerens from olive orchards with two decades of multiple herbicides use.
Authors: Palma-Bautista, Candelario1 (AUTHOR), Rojano-Delgado, Antonia M.2 (AUTHOR), Rey, María-Dolores1,3 (AUTHOR) b52resam@uco.es, Gherekhloo, Javid4 (AUTHOR), Domínguez-Valenzuela, José A.1 (AUTHOR), Jorrín-Novo, Jesús V.3 (AUTHOR), Plaza, Guido5 (AUTHOR), Osuna, María D.6 (AUTHOR), De Prado, Rafael3 (AUTHOR)
Source: Pesticide Biochemistry & Physiology. Feb2026, Vol. 217, pN.PAG-N.PAG. 1p.
Subject Terms: *Herbicide resistance, *Weed control, Cytochrome P-450, Orchards, Setaria, Multidrug resistance
Geographic Terms: Spain
Abstract: Two populations of Setaria adhaerens (resistant [R] and susceptible [S]) have been identified in Spanish olive orchards. The R population shows multiple resistance to chlorotoluron (PSII inhibitor), diclofop-methyl (ACCase inhibitor), tribenuron-methyl (ALS inhibitor), glyphosate (EPSPS inhibitor), and oxyfluorfen (PPO inhibitor), along with potential natural tolerance to diflufenican (PDS inhibitor). This study evaluated herbicide efficacy at field rates, enzyme activity (ALS, ACCase, EPSPS, PPO, PSII), and the role of cytochrome P450 and glutathione-S-transferases using malathion and NBD-Cl, respectively. The S population was fully controlled by all herbicides except diflufenican, which showed only ∼45 % control in both populations, indicating possible innate tolerance. In the R population, chlorotoluron, diclofop-methyl, tribenuron-methyl, and glyphosate had no effect on enzyme activity, suggesting non-target site resistance (NTSR). In contrast, oxyfluorfen inhibited PPO activity only in the S population, indicating target-site resistance (TSR). NBD-Cl showed no activity, ruling out glutathione-S-transferases-mediated metabolism. However, malathion restored over 50 % sensitivity to chlorotoluron, diclofop-methyl, and tribenuron-methyl in the R population, suggesting enhanced metabolism likely mediated by cytochrome P450 monooxygenases. Metabolic profiling further confirmed enhanced herbicide detoxification in the R population as a key resistance mechanism. These findings highlight the complexity of resistance in S. adhaerens and underline the urgent need to incorporate metabolic resistance monitoring into weed management programs. Future studies will focus on unraveling the molecular basis of these resistance mechanisms. Main message: Setaria adhaerens from Spanish olive orchards exhibits complex multiple resistance, involving both target-site and cytochrome P450-mediated metabolic mechanisms, highlighting the need to monitor metabolic resistance in weed management. [Display omitted] • First case of multiple herbicide resistance in Setaria adhaerens in Spain. • Reduced control with ACCase, ALS, EPSPS, PPO, and PSII inhibitor herbicides. • Cytochrome P450 enzymes drive enhanced metabolism of several herbicides. • Glyphosate degradation to sarcosine revealed as a novel resistance mechanism. [ABSTRACT FROM AUTHOR]
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Abstract:Two populations of Setaria adhaerens (resistant [R] and susceptible [S]) have been identified in Spanish olive orchards. The R population shows multiple resistance to chlorotoluron (PSII inhibitor), diclofop-methyl (ACCase inhibitor), tribenuron-methyl (ALS inhibitor), glyphosate (EPSPS inhibitor), and oxyfluorfen (PPO inhibitor), along with potential natural tolerance to diflufenican (PDS inhibitor). This study evaluated herbicide efficacy at field rates, enzyme activity (ALS, ACCase, EPSPS, PPO, PSII), and the role of cytochrome P450 and glutathione-S-transferases using malathion and NBD-Cl, respectively. The S population was fully controlled by all herbicides except diflufenican, which showed only ∼45 % control in both populations, indicating possible innate tolerance. In the R population, chlorotoluron, diclofop-methyl, tribenuron-methyl, and glyphosate had no effect on enzyme activity, suggesting non-target site resistance (NTSR). In contrast, oxyfluorfen inhibited PPO activity only in the S population, indicating target-site resistance (TSR). NBD-Cl showed no activity, ruling out glutathione-S-transferases-mediated metabolism. However, malathion restored over 50 % sensitivity to chlorotoluron, diclofop-methyl, and tribenuron-methyl in the R population, suggesting enhanced metabolism likely mediated by cytochrome P450 monooxygenases. Metabolic profiling further confirmed enhanced herbicide detoxification in the R population as a key resistance mechanism. These findings highlight the complexity of resistance in S. adhaerens and underline the urgent need to incorporate metabolic resistance monitoring into weed management programs. Future studies will focus on unraveling the molecular basis of these resistance mechanisms. Main message: Setaria adhaerens from Spanish olive orchards exhibits complex multiple resistance, involving both target-site and cytochrome P450-mediated metabolic mechanisms, highlighting the need to monitor metabolic resistance in weed management. [Display omitted] • First case of multiple herbicide resistance in Setaria adhaerens in Spain. • Reduced control with ACCase, ALS, EPSPS, PPO, and PSII inhibitor herbicides. • Cytochrome P450 enzymes drive enhanced metabolism of several herbicides. • Glyphosate degradation to sarcosine revealed as a novel resistance mechanism. [ABSTRACT FROM AUTHOR]
ISSN:00483575
DOI:10.1016/j.pestbp.2025.106883