Biotechnology: Herbicide-Resistant Crops

Two major classes of herbicides include inhibitors of protoporphyrinogen oxidase (PPO) and phytoene desaturase (PDS). Plants can evolve resistance to PPO and PDS inhibitors via several mechanisms that include physical changes, resulting in reduced uptake, physiological changes, resulting in compartmentalization or altered translocation, and biochemical changes, resulting in enhanced metabolic degradation or alterations of protein structures, leading to loss of sensitivity to the herbicides. This review discusses the involvement of some of these mechanisms in the various cases of resistance to PDS- and PPO-inhibiting herbicides, and highlights unique aspects of target-site resistance to these herbicides.

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Evolution of resistance to phytoene desaturase and protoporphyrinogen oxidase inhibitors – state of knowledge

Dayan

Owens

Tranel

et al. 2014

“…The positive impact was perhaps even greater for small farmers who had neither the expertise nor budget for consultants to generate prescription herbicide remedies for specific weed problems. The economic and efficacy reasons for this outstanding success have been detailed in many publications . Furthermore, this technology reduced the environmental impact of weed management through reductions in tillage, fossil fuel use, and the use of more toxic herbicides, detailed in many previous reviews .…”

Section: The Golden Age Of Weed Management; the First Ten Years Of Glmentioning

confidence: 99%

The history and current status of glyphosate

Duke

2017

374

248

Glyphosate is the only herbicide to target the enzyme 5-enolpyruvyl-3-shikimate phosphate synthase (EPSPS). It is a high use rate, non-selective herbicide that translocates primarily to metabolic sinks, killing meristematic tissues away from the application site. Its phloem-mobile properties and slow action in killing weeds allow the herbicide to move throughout the plant to kill all meristems, making it effective for perennial weed control. Since commercialization in 1974, its use has grown to dominate the herbicide market. Much of its use is on transgenic, glyphosate-resistant crops (GRCs), which have been the dominant transgenic crops worldwide. GRCs with glyphosate provided the most effective and inexpensive weed management technology in history for a decade or more. However, as a consequence of the rapid increase in glyphosate-resistant (GR) weeds, the effectiveness of glyphosate use in GRCs is declining. Critics have claimed that glyphosate-treated GRCs have altered mineral nutrition and increased susceptibility to plant pathogens because of glyphosate's ability to chelate divalent metal cations, but the complete resistance of GRCs to glyphosate indicates that chelating metal cations do not contribute to the herbicidal activity or significantly affect mineral nutrition. The rates of increases in yields of maize, soybean, and cotton in the USA have been unchanged after high adoption rates of GRCs. Glyphosate is toxic to some plant pathogens, and thereby can act as a fungicide in GRCs. Ultra-low doses of glyphosate stimulate plant growth in glyphosate-susceptible plants by unknown mechanisms. Despite rapid and widespread increases in GR weeds, glyphosate use has not decreased. However, as GR weeds increase, adoption of alternative technologies will eventually lead to decreased use. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

“…), in large part due to the increase in glyphosate usage in glyphosate‐resistant crops. The effectiveness of glyphosate in glyphosate‐resistant crops, combined with its broad spectrum of control at a relatively low cost, led to a rapid adoption rate in soybean, corn, cotton, canola and sugarbeet , . The reduction in the cost of weed control due to the introduction of glyphosate‐resistant crops had an adverse effect on the profitability of introducing new herbicides, resulting in a subsequent reduction in herbicide discovery programs (Fig.…”

Section: Introductionmentioning

confidence: 99%

Overview of glyphosate‐resistant weeds worldwide

Heap¹,

Duke

2017

391

287

Glyphosate is the most widely used and successful herbicide discovered to date, but its utility is now threatened by the occurrence of several glyphosate-resistant weed species. Glyphosate resistance first appeared in Lolium rigidum in an apple orchard in Australia in 1996, ironically the year that the first glyphosate-resistant crop (soybean) was introduced in the USA. Thirty-eight weed species have now evolved resistance to glyphosate, distributed across 37 countries and in 34 different crops and six non-crop situations. Although glyphosate-resistant weeds have been identified in orchards, vineyards, plantations, cereals, fallow and non-crop situations, it is the glyphosate-resistant weeds in glyphosate-resistant crop systems that dominate the area infested and growing economic impact. Glyphosate-resistant weeds present the greatest threat to sustained weed control in major agronomic crops because this herbicide is used to control weeds with resistance to herbicides with other sites of action, and no new herbicide sites of action have been introduced for over 30 years. Industry has responded by developing herbicide resistance traits in major crops that allow existing herbicides to be used in a new way. However, over reliance on these traits will result in multiple-resistance in weeds. Weed control in major crops is at a precarious point, where we must maintain the utility of the herbicides we have until we can transition to new weed management technologies. © 2017 Society of Chemical Industry.