Effect of glyphosate on the physiological parameters of horseweed

Abstract

The aim of this study was to determine changes in the photosynthetic process and the inhibition of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPs) by shikimic acid accumulation, after application of the herbicide glyphosate in four biotypes of C. sumatrensis collected in the state of Rio Grande do Sul. Therefore, the experiments were conducted under greenhouse and laboratory, assessing plant biomass, photosynthesis rate, transpiration and water use efficiency; the amount of shikimic acid was calculated for each treatment. Glyphosate application reduced growth and affected the photosynthesis rate and water use efficiency of the biotypes differentially, and the resistant biotype had small interference from glyphosate, while physiological parameters of the susceptible biotype were deeply affected by the herbicide. Susceptible biotypes had higher shikimic acid accumulation than the resistant biotype, indicating differential sensitivity of EPSPs to glyphosate between resistant and sensitive biotypes. Key words: Conyza sumatrensis, EPSPs, resistance, shikimic acidEfeito do glyphosate sobre parâmetros fisiológicos de buva RESUMO O objetivo do trabalho foi determinar alterações no processo fotossintético e na inibição da 5-enolpiruvilchiquimato-3-fosfato sintase (EPSPs), por meio do acúmulo de ácido chiquímico, após a aplicação do herbicida glyphosate, em quatro biótipos de C. sumatrensis coletados no Estado do Rio Grande do Sul. Para isto foram conduzidos experimentos em casa-de-vegetação e em laboratório avaliando fitomassa seca da parte aérea, taxa de fotossíntese, transpiração e eficiência do uso da água; a quantidade de ácido chiquímico foi calculada para cada tratamento. A aplicação do glyphosate reduziu o crescimento e afetou a taxa de fotossíntese a eficiência do uso da água dos biótipos de forma diferencial, sendo que o biótipo resistente teve pequena interferência do glyphosate enquanto os parâmetros fisiológicos do biótipo suscetível foram profundamente afetados pelo herbicida. Nos biótipos suscetíveis o acúmulo de ácido chiquímico foi maior que no biótipo resistente evidenciando sensibilidade diferencial da EPSPs dos biótipos resistente e sensíveis ao glyphosate. Palavras

Influence of Glyphosate on Susceptible and Resistant Ryegrass Populations to Herbicide

“…The resistant population, however, remained with positive values similar to those of the resistant control. Similar results were found by Santos et al (2014) when evaluating the effects of glyphosate on the photosynthesis in horseweed resistant and susceptible to this herbicide. These authors observed that, at 3 DAA, both biotypes showed a reduction in the assimilation of CO 2 in relation to the control and this result was extended up to 10 DAA.…”

Molecular Characterization of Hairy Fleabane Using Rapd

“…In the State, there are three already identified species of Conyza that are resistant to glyphosate: C. bonariensis, C. canadensis and C. sumatrensis (Vargas et al, 2007;Lamego and Vidal, 2008;Santos et al, 2014). Even though the occurrence of glyphosate resistant Conyza sp.…”

“…C. canadensis and C. sumatrensis), there is the possibility of breeding between the other species, which might result in the increase of the resistance level, as shown through the hybridization between glyphosate resistant C. canadensis with C. ramosissima, susceptible species (Zelaya et al, 2007). All the same, as a result from the breeding between species, morphological variations from the generated phenotypes may occur, which interfere in the herbicide-plant relation, as, for example, a greater presence of trichomes on the leaves, which may be associated to tolerance in the absorption of herbicides (Zelaya et al, 2007;Santos et al, 2014).…”

“…In the high flat regions of the State, important for its soybean production and where the biotypes of glyphosate resistant hairy fleabane occur, species of C. bonariensis microcephala varieties, C. chilensis and C. sumatrensis were observed. (Schneider and Irgang, 2005;Santos et al, 2014). Guareschi et al (2012) verified the presence of the microcephala varieties of (Ritter and Baptista, 2005).…”