glyphosate

Lolium rigidum (annual ryegrass) is a species that is prone to evolve resistance to a wide range of herbicide modes of action. Rapid detection of herbicide-resistant weed populations in the field can aid farmers to optimise the use of effective herbicides for their control.

Glyphosate is often tank-mixed with auxinic herbicide 2,4-D for grass and broadleaf weed control. In this paper, the authors examined the possible interaction of 2,4-D and glyphosate in barnyard grass, Echinochloa colona. The results showed that 2,4-D antagonizes glyphosate remarkably in glyphosate resistant populations but only marginally in susceptible populations. This antagonism is related to reduced glyphosate uptake and (to a lesser extent) translocation. As 2,4-D has multiple, unpredictable effects on other herbicides, care must be taken when tank-mixing herbicides with 2,4-D.

This paper reviews the literature to understand the effects of glyphosate resistance on plant fitness at the molecular, biochemical and physiological levels. A number of correlations between enzyme characteristics and glyphosate resistance imply the existence of a plant fitness cost associated with resistance-conferring mutations in the glyphosate target enzyme, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). These biochemical changes result in a tradeoff between the glyphosate resistance of the EPSPS enzyme and its catalytic activity.

Earlier papers by Gaines et al 2012 Weed Technology and Goh et al 2016 Pest Management Science, documented a glyphosate resistance Echinochloa population from the irrigated north-west Ord River irrigation region of Western Australia. AHRI PhD student Sou Sheng Goh studied this population for his PhD research. Among other studies, Goh completed excellent work to identify the mechanistic basis of glyphosate resistance in this Echinochloa population. Goh examined for but did not find EPSPS resistance gene mutations and/or EPSPS gene amplification. Thus Goh established that glyphosate resistance in this particular resistant biotype is NON-target site based. 

In the last two decades the cultivation of transgenic crops has steadily increased worldwide. In Western Australia transgenic glyphosate-resistant canola (GR) has been cultivated since 2009. This study was conducted to examine the potential for transgene persistence outside agricultural fields after commercialization of GR crops.

Lolium rigidum (annual or rigid ryegrass) is a widespread annual weed in cropping systems of southern Australia, and herbicide resistance in L. rigidum is a common problem in this region. In 2010, a random survey was conducted across the grain belt of Western Australia to determine the frequency of herbicide-resistant L. rigidum populations and to compare this with the results of previous surveys in 1998 and 2003.

In Australia, glyphosate has been used routinely to control wild radish (Raphanus raphanistrum L.) for the past 40 years. This study focuses on two field-evolved glyphosate-resistant populations of wild radish collected from the grainbelt of Western Australia.

Weed populations can have high genetic plasticity and rapid responses to environmental selection pressures. For example, 100-fold amplification of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene evolved in the weed species Amaranthus palmeri to confer resistance to glyphosate, the world’s most important herbicide.

In a large cropping area of northern Argentina, Sorghum halepense (Johnsongrass) has evolved towards glyphosate resistance. This study aimed to determine the molecular and biochemical basis conferring glyphosate resistance in this species. Experiments were conducted to assess target EPSPS gene sequences and 14C-glyphosate leaf absorption and translocation to meristematic tissues.

The objective of this study was to determine whether a junglerice population from the tropical Ord River region of northwest Australia was glyphosate resistant, and whether alternative herbicides labeled for junglerice control were still effective.