Banca de DEFESA: RITA DE CÁSSIA SILVA

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : RITA DE CÁSSIA SILVA
DATE: 05/03/2026
TIME: 13:30
LOCAL: Online
TITLE:

Physiological modulation of glufosinate-ammonium herbicide efficacy by light

KEY WORDS:

photosynthesis; glutamine synthetase; glutathione S-transferase; post-emergence; contact herbicide.

PAGES: 118
BIG AREA: Ciências Agrárias
AREA: Agronomia
SUBÁREA: Fitotecnia
SPECIALTY: Matologia
SUMMARY:

Light is an environmental factor that strongly influences the efficacy of the herbicide glufosinate-ammonium, affecting weed control under field conditions. The objective of this research was to understand how light intensity modulates the photochemical, biochemical, and antioxidant mechanisms involved in the action of glufosinate-ammonium, and how this modulation impacts weed control efficacy. Three experiments were conducted with the following specific objectives: to evaluate the photosynthetic and antioxidant metabolism of Amaranthus hybridus in response to glufosinate-ammonium under full sunlight and dark conditions (Chapter I); to investigate the role of herbicide-metabolizing enzymes in the physiological response of Amaranthus hybridus treated with glufosinate-ammonium under the absence of light (Chapter II); and to assess the influence of different light intensities on the physiological response of Amaranthus hybridus and Eleusine indica treated with glufosinate-based products (Chapter III). Light is an environmental factor that strongly influences the efficacy of the herbicide glufosinate-ammonium, affecting weed control under field conditions. The objective of this research was to understand how light intensity modulates the photochemical, biochemical, and antioxidant mechanisms involved in the action of glufosinate-ammonium, and how this modulation impacts weed control efficacy. Three experiments were conducted with the following specific objectives: to evaluate the photosynthetic and antioxidant metabolism of Amaranthus hybridus in response to glufosinate-ammonium under full sunlight and dark conditions (Chapter I); to investigate the role of herbicide-metabolizing enzymes in the physiological response of Amaranthus hybridus treated with glufosinate-ammonium under the absence of light (Chapter II); and to assess the influence of different light intensities on the physiological response of Amaranthus hybridus and Eleusine indica treated with glufosinate-based products (Chapter III). In Chapter II, glufosinate application in the dark resulted in low control of A. hybridus, regardless of the use of metabolic inhibitors. Glutamine synthetase was rapidly inhibited in all treatments; however, changes in photosynthetic parameters appeared later and were reversible at 12 hours after application, followed by recovery of the photosynthetic apparatus and plant regrowth at 14 days. Inhibition of GST and cytochrome P450 did not increase glufosinate efficacy nor alter plant physiological responses. These results suggest that the reduced efficacy of glufosinate under dark conditions is not associated with GST- or cytochrome P450-mediated metabolism, but rather with the dependence on photosynthetic activity for amplification of oxidative stress. In Chapter III, in Eleusine indica, glufosinate caused initial injury under all shading conditions, regardless of formulation, with more intense photochemical stress under 0% cloud cover. GS was rapidly inhibited and GST activity increased; however, plant growth recovery was observed over time. In contrast, Amaranthus hybridus showed 100% control under all light conditions, with rapid photosynthetic damage, GS inhibition, and increased GST activity. Light intensity influenced herbicide response, but the effect was species dependent.

COMMITTEE MEMBERS:
Presidente - 2466219 - CAMILA FERREIRA DE PINHO
Interno - 1905333 - AROLDO FERREIRA LOPES MACHADO
Externa à Instituição - GABRIELA DE SOUZA DA SILVA - UFRRJ
Externo à Instituição - GILIARDI DALAZEN - UEL
Externo à Instituição - RUBEM SILVÉRIO DE OLIVEIRA JUNIOR - UEM