Resistance to glyphosate

To illustrate engineered resistance, we may use some data from Amaud et al. (1998), summarized in Table 9.5. A gene from Salmonella (aroA) encodes a glyphosate-tolerant EPSP synthase. EPSP synthase is the target enzyme for 

Note The activity (nkat) is in nmol EPSP produced per second in leaves or roots. Inhibition (Igo) is in pmol glyphosate. 

The levels of EPSP synthase activity were much higher in HR plants than in WR plants and S plants. 

The I50 (the glyphosate concentration necessary to inhibit 50% of the enzyme activity) of EPSP synthase was much higher in leaves of WR plants than in HR plants, in contrast to the situation inside the roots. 

High levels of EPS synthase were maintained in the HR plants, from seedlings to 3-month-old plants, but the overproduction of EPSP synthase decreased in WR plants when they grew older. 

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Other developments include the introduction of hybrid lines resistant to glyphosate and glufosinate. Glyphosate-resistance technology was rapidly adopted for soybean, but was more slowly adopted for field corn due to corn s slower canopy closure. Acceptance of glufosinate-resistant weed control technology faced the same obstacles, but has been even less competitive economically due to product cost. 

Several weed species resistant to glyphosate have recently developed in several geographical areas of the United States. This further supports the need for keeping a broad range of herbicides, such as the triazines, available for weed management programs. 

Padgette, S.R., X. Delannay, L.D. Bradshaw, B.H. Wells, and G. Kishore (1995). Development of glyphosate-tolerant crops and perspectives on the potential for weed resistance to glyphosate, p. 154. In De Prado, R., Garcia-Torres, L., and Jorrin, J., eds., International Symposium on Weed and Crop Resistance to Herbicides. Cardoba, Spain Cardobesa de Impresiones Graficas, SL. Abstract, 92. 

Powles, S.B., D.F. Lorraine-Colwill, J.J. Dellow, and C. Preston (1998). Evolved resistance to glyphosate in rigid ryegrass (Lolium rigidum) in Australia. Weed Sci., 46 604—607. 

Similarly, a variety of arguments was put forward as to why resistance to glyphosate was very unlikely to occur. Apparently the weeds were not listening, as glyphosate resistance has now developed in at least four weed species [1]. The process has been slow and the frequency very low, but it took resistant weeds in farmers fields to convince us it could happen. 

Physiological behavior of two tobacco lines expressing EPSP synthase resistant to glyphosate. Pest. Biochem. Physiol., 62, 27-39. 

Some of the weed species, such as Euphorbia esculenta, Equisaetum arvertse, Hedera helix and Robia peregrina, are resistant to glyphosate. (Gottrup et al., 1976 Kafadaroff et al., 1977). 

Atrazine resistance and plants made resistant by genetic engineering Resistance to glyphosate 9.3.5.1 Summary... 

Clyphosate Resistance to glyphosate has now appeared in several weed species. 

EPSP synthases resistant to glyphosate have been identified and partially characterized in glyphosate-resistant mutants of S. typhimurium and K. 

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