RESUMO
BACKGROUND: Resistance to 2,4-Dichlorophenoxyacetic acid (2,4-D) has been reported in several weed species since the 1950s; however, a biotype of Conyza sumatrensis showing a novel physiology of the rapid response minutes after herbicide application was reported in 2017. The objective of this research was to investigate the mechanisms of resistance and identify transcripts associated with the rapid physiological response of C. sumatrensis to 2,4-D herbicide. RESULTS: Differences were found in 2,4-D absorption between the resistant and susceptible biotypes. Herbicide translocation was reduced in the resistant biotype compared to the susceptible. In resistant plants 98.8% of [14 C] 2,4-D was found in the treated leaf, whereas ≈13% translocated to other plant parts in the susceptible biotype at 96 h after treatment. Resistant plants did not metabolize [14 C] 2,4-D and had only intact [14 C] 2,4-D at 96 h after application, whereas susceptible plants metabolized [14 C] 2,4-D into four detected metabolites, consistent with reversible conjugation metabolites found in other 2,4-D sensitive plant species. Pre-treatment with the cytochrome P450 inhibitor malathion did not enhance 2,4-D sensitivity in either biotype. Following treatment with 2,4-D, resistant plants showed increased expression of transcripts within plant defense response and hypersensitivity pathways, whereas both sensitive and resistant plants showed increased expression of auxin-response transcripts. CONCLUSION: Our results demonstrate that reduced 2,4-D translocation contributes to resistance in the C. sumatrensis biotype. The reduction in 2,4-D transport is likely to be a consequence of the rapid physiological response to 2,4-D in resistant C. sumatrensis. Resistant plants had increased expression of auxin-responsive transcripts, indicating that a target-site mechanism is unlikely. © 2023 Society of Chemical Industry.
Assuntos
Conyza , Herbicidas , Conyza/genética , Resistência a Herbicidas/genética , Herbicidas/farmacologia , Herbicidas/metabolismo , Ácido 2,4-Diclorofenoxiacético/farmacologia , Expressão GênicaRESUMO
Glyphosate has been the most widely used herbicide for decades providing a unique tool, alone or in mixtures, to control weeds on citrus in Veracruz. Conyza canadensis has developed glyphosate resistance for the first time in Mexico. The level and mechanisms of resistance of four resistant populations Rs (R1, R2, R3, and R4) were studied and compared with that of a susceptible population (S). Resistance factor levels showed two moderately resistant populations (R2 and R3) and two highly resistant populations (R1 and R4). Glyphosate translocation through leaves to roots was â¼2.8 times higher in the S population than in the four R populations. A mutation (Pro106Ser) in the EPSPS2 gene was identified in the R1 and R4 populations. Mutation in the target site associated with reduced translocation is involved in increased glyphosate resistance in the R1 and R4 populations; whereas for the R2 and R3 populations, it was only mediated by reduced translocation. This is the first study of glyphosate resistance in C. canadensis from Mexico in which the resistance mechanisms involved are described in detail and control alternatives are proposed.