A comprehensive study of 2,4-D resistance mechanisms in Conyza sumatrensis

• Autor(a) principal: Baccin, Luisa Carolina
• Data de Publicação: 2024
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: https://www.teses.usp.br/teses/disponiveis/11/11136/tde-13052024-114140/
• topic: Biochemical responses; Buva; Estresse fisiológico; Fenômeno Fênix; Herbicide translocation; Horseweed; Phoenix phenomenon; Physiological stress; Respostas bioquímicas; Translocação de herbicidas

Herbicide resistance in weeds represents a critical challenge in modern agriculture, significantly affecting crop yields and sustainability. Particularly concerning is the resistance observed in Conyza species, a group of weeds known for their robust adaptability and competitive growth. These species, often found in agricultural fields worldwide, compete aggressively with crops for resources. This thesis presents an in-depth examination of the resistance mechanisms to widely used herbicides, focusing on the increasing resistance of Conyza sumatrensis (Retz.) to 2,4-D (2,4-dichlorophenoxyacetic acid). The study integrates comprehensive literature reviews with empirical research to elucidate the complexities of this resistance, providing a holistic view of the issue. The initial part of the thesis comprises a published literature review, which identifies global instances of Conyza spp. resistance to various herbicides. It presents the known resistance mechanisms, laying a solid foundation for experimental investigations since it contextualizes the research within the broader spectrum of herbicide resistance studies, allowing for a deeper understanding of the emerging trends and patterns. The research then advances into experimental dose-response assays, along with greenhouse and laboratory studies, to evaluate the cross-resistance of Conyza sumatrensis to other auxin herbicides. This includes studying the leaf disc solution conductivity, which helps assess the rapid response to 2,4-D. Additionally, the research explores potential promoters and inhibitors of these responses, providing valuable insights into the physiological and biochemical behaviors of Conyza sumatrensis under herbicidal stress. This comprehensive analysis is extended by laboratory studies evaluating chlorophyll fluorescence and physiological responses, including photosynthesis in both R and S biotypes. A significant focus of the thesis is on the rapid response to 2,4-D, a new mechanism of resistance being studied in Conyza sumatrensis. This phenomenon, described in the literature as the \'Phoenix Phenomenon\', is characterized by the necrosis of leaves just hours after herbicide exposure. This aspect of the study is pivotal in understanding the immediacy and severity of the plant\'s response to herbicidal application, a factor crucial for developing effective weed management strategies. Moreover, the mechanisms of resistance are explored by examining the uptake and translocation of 14C-2,4-D in Conyza sumatrensis under different lighting conditions. Malondialdehyde (MDA) and hydrogen peroxide (H2O2) levels were measured to assess oxidative stress, alongside analyzing enzyme expression in resistant (R) and susceptible (S) biotypes. These studies offer a deeper understanding of how Conyza sumatrensis biotypes differentially respond to herbicidal stress at a cellular level. The findings enhance our knowledge of herbicide resistance mechanisms and have significant implications for integrated weed management strategies. By combining empirical research with practical agricultural applications, this work underscores the need for a multifaceted approach to tackle herbicide resistance. It is poised to guide future research and inform the development of sustainable herbicide usage methods, contributing to the effective management of herbicide-resistant weed populations and aiding in the preservation of agricultural productivity.