Banca de DEFESA: IGOR NUNES BARCELLOS DA COSTA

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : IGOR NUNES BARCELLOS DA COSTA
DATE: 31/08/2026
TIME: 13:00
LOCAL: online
TITLE:

Characterization of NTSR resistance in Conyza sumatrensis under different temperatures

KEY WORDS:

Oxidative stress; redox homeostasis; systemic translocation; vacuolar compartmentalization.

PAGES: 124
BIG AREA: Ciências Agrárias
AREA: Agronomia
SUBÁREA: Fitotecnia
SPECIALTY: Matologia
SUMMARY:

Non-target-site resistance (NTSR) represents a major challenge for weed management because it may involve alterations in herbicide absorption, translocation, compartmentalization, metabolism, and cellular protection against herbicide-induced damage, thereby complicating the control of these species. Furthermore, the expression of these mechanisms may vary according to environmental conditions, particularly temperature. This study aimed to evaluate the influence of temperatures of 18 and 30 °C on the efficacy of diquat and glyphosate and to characterize the photochemical, physiological, oxidative, antioxidant, and detoxification-related responses in resistant and susceptible biotypes of Conyza sumatrensis. Two independent experiments were conducted under controlled conditions, each arranged in a 2 × 2 factorial design consisting of resistant and susceptible biotypes and temperatures of 18 and 30 °C, in a completely randomized design with four replications. Herbicides were applied to plants with 15 to 20 leaves. Visual control was assessed up to 28 days after application (DAA), together with gas exchange, chlorophyll a transient fluorescence, OJIP curves, reactive oxygen species, lipid peroxidation, and the activities of antioxidant enzymes and enzymes associated with glutathione metabolism. In the diquat experiment, high temperature rapidly intensified the herbicide’s redox cycling, resulting in increased production of O₂•⁻ and H₂O₂, elevated MDA levels, reduced net photosynthesis, and early impairment of electron transport and the indices PIABS, PItotal, φRo, and RE₀/RC. At 28 DAA, the susceptible biotype died at 30 °C, whereas at 18 °C it exhibited regrowth. The resistant biotype survived at both temperatures, with lower control under cooler conditions. Greater GR activity at 18 °C, associated with reduced membrane lipid peroxidation, indicated more efficient preservation of redox homeostasis, limiting the progression of initial stress into irreversible damage. In contrast, glyphosate produced the opposite response. At 28 DAA, the resistant biotype exhibited 96.25% control at 18 °C and 13.75% at 30 °C, whereas the susceptible biotype showed 86.67% and 35.00% control, respectively. Under low temperature, the effects were initially less abrupt but progressed to persistent reductions in carbon assimilation and impairment of electron transport extending to the final electron acceptors of Photosystem I. APX and GST activities were higher at 18 °C, and γ-glutamyl transferase showed distinct temporal responses between biotypes, indicating mobilization of vacuolar glutathione metabolism without confirming protective herbicide sequestration. It is concluded that temperature modulated herbicide efficacy and the phenotypic expression of resistance in contrasting ways. High temperature enhanced the oxidative action and weed control provided by diquat, whereas low temperature preserved antioxidant mechanisms. For glyphosate, low temperature suppressed resistance and promoted a more persistent systemic herbicidal effect, whereas high temperature allowed the survival of both biotypes, probably due to changes in herbicide availability, translocation, or cellular compartmentalization.

COMMITTEE MEMBERS:
Interna - 2466219 - CAMILA FERREIRA DE PINHO
Interno - 2181674 - LEONARDO OLIVEIRA MEDICI
Externo à Instituição - ALFREDO JUNIOR PAIOLA ALBRECHT