Perspectives on Glyphosate Resistance

Abstract

The lack of evolution of weed resistance to the herbicide glyphosate has been considered from several perspectives. Few plant species are inherently resistant to glyphosate. Furthermore, the long history of extensive use of the herbicide has resulted in no verified instances of weeds evolving resistance under field situations. Unique properties of glyphosate such as its mode of action, metabolism, chemical structure and lack of residual activity in soil may explain this observation. Selection for glyphosate resistance of crops using intense whole plant and cell/tissue culture techniques, including mutagenesis, has had only limited success and is unlikely to be duplicated under normal field conditions. Information obtained in the development of glyphosate-resistant crops suggests that target-site alterations that decrease the herbicidal activity of glyphosate also may lead to reduced survival of a weed. In addition, the complex manipulations that were required for the development of glyphosate-resistant crops are unlikely to be duplicated in nature to evolve glyphosate-resistant weeds.

A Modified phosphate-carrier protein theory is proposed as a non-target site mechanism For glyphosate resistance in weeds

“…Although glyphosate has been commercialized since 1974 (Vidal & Merotto Jr., 2001), the first reports of weeds resistant to glyphosate came in 1996, which lead many authors to believe that weed resistance to glyphosate would be unlikely to occur (Waters, 1991;Jasieniuk, 1995;Bradshaw et al, 1997). Three main reasons were presented to support this hypothesis.…”

“…Second, overexpression of EPSPs gene confers low levels of resistance. Third, mutations on EPSPs gene were associated with high fitness penalties (Waters, 1991;Jasieniuk, 1995;Bradshaw et al, 1997).…”

Ecological Impacts of Genetically Modified Crops: Ten Years of Field Research and Commercial Cultivation

“…The commercialization of herbicides inhibiting acetolactat synthase (ALS), for example, induced the evolution of herbicide-resistant biotypes in over 90 weed species, while 65 weed species have evolved resistance to atrazine [143,144]. It seems that tolerance to glyphosate, in contrast, is less likely to develop in weed species (and in volunteers) than tolerance to other herbicides, as a result of its chemical properties and its mode of action [145,146]. After almost three decades of glyphosate use, tolerance to glyphosate has only been reported in eight weed species worldwide [143].…”

Produtividade de grãos da soja em função do manejo de herbicida e fungicidas

“…A soja transgênica (RR), geneticamente modificada com um gene que codifica a enzima EPSPS, torna-se tolerante à ação do glifosato. Isso significa que a soja RR continua produzindo compostos essenciais ao seu desenvolvimento e crescimento, não sendo afetada pelos efeitos do herbicida (BRADSHAW et al, 1997).…”