Triazine resistance

Triazine Resistance Amino Acid Substitutions in the D1 Protein... 

Cross-Resistance to Other Herbicides in Triazine Resistance... 

Radosevich, S.R. and O.T. DeVilliers (1976). Studies on the mechanism of s-triazine resistance in common groundsel. Weed Sci. 24 229-232. 

Vermass, W.F.J. and C.J. Arntzen (1984). Synthetic quinones influencing herbicide binding and photosystem II electron transport. The effects of triazine-resistance on quinone binding properties in thylakoid membranes. Biochim. Biophys. Acta., 725 483 -91. 

Triazines were one of the first family of herbicides where weed resistance was widely recognized and documented in the literature. A simazine-resistant biotype of common groundsel was identified in Washington, United States, in 1968. Since then biotypes of at least 66 triazine-resistant weed species have been reported, mostly in the United States, Canada, and Europe (Heap, 2006). 

Triazine herbicides provide selective weed control in crops such as corn, sorghum, and sugarcane. In addition, some members of the triazine family are used for weed control in orchards, horticultural, and perennial crops, etc. A unique selective use of triazine herbicides is in triazine-tolerant rapeseed. Although triazine herbicides provide control of a wide variety of grass and broadleaf weeds, the long-term, widespread, and repetitive use of triazine herbicides in crop and noncrop situations has led to the selection of many triazine-resistant weeds. The physiological and biochemical basis of triazine selectivity between crops and weeds and of resistance to triazine herbicides in weeds is well understood. 

Weed resistance to the triazine herbicides was first identified in the late 1960s, with a biotype of common groundsel that was resistant to simazine (Ryan, 1970). Since then, resistance to triazine herbicides has been reported in many weed species (Holt and LeBaron, 1990 LeBaron and McFarland, 1990 Gronwald, 1994). Most cases of triazine resistance have been reported in the US, Canada, and Europe, where triazine herbicides have been used extensively in corn monocultures (LeBaron and McFarland, 1990 Stephenson et al., 1990 LeBaron, 1991). Most of the. v-triazinc-resistant weed species have been selected against atrazine and usually show a high level of cross-resistance to other. v-triazine herbicides. In most cases, these weeds also show a low level of resistance to as-triazinones (e.g., metribuzin). Triazine-resistant weeds are often less vigorous than nonresistant weeds, which facilitates their management. 

In practical terms, the Ser264 to Gly mutation causing triazine resistance reduces plant productivity and yield. This has two agronomic implications first, triazine-resistant weeds carrying this mutation are less competitive (often referred in the literature as reduced fitness) on a per plant basis as compared to their susceptible counterparts, and second, triazine-resistant rapeseed cultivars with Hie mutant psbA gene are less productive than near isogenic, susceptible cultivars (Forcella, 1987 Beversdorf et al, 1988 Hart and Stemler, 1990 Hall et al, 1996). 

In summary, triazine resistance in weeds is most commonly due to a target site alteration that confers a very high level of resistance to. y-triazinc herbicides. Although a Ser264 to Gly mutation in the D1 protein is most common, additional alterations have been identified that confer resistance to triazines and other classes of PS II inhibitors. Enhanced herbicide metabolism plays a major role in conferring resistance in only a few weed biotypes. In these biotypes, the pattern of resistance may be broader, with some cross-resistance to av-trazinones, uracils, heterocyclic ureas and phenyl ureas. The level and pattern of resistance to various herbicides in these biotypes depend, presumably, on the activity and specificity of the enzyme(s) responsible for the enhanced herbicide metabolism. 

The high efficacy of triazine herbicides and their repetitive use in crops and noncrop situations has resulted in the selection of weeds that are resistant to these herbicides or are not well controlled at the lower rates now being used. In most instances, triazine resistance is due to an alteration in the herbicide-binding site in PS II. Despite the widespread occurrence of triazine resistance, these herbicides are still widely used, even in fields in which triazine-resistant biotypes are known to occur. The rate of increase in the selection for triazine-resistant weed species depends in part on the integration of alternative weed control strategies, in addition to the use of triazine herbicides, for control of these weed species. Due to their resistance mechanism, many triazine-resistant weeds are less competitive than their susceptible counterparts. 

Beversdorf, W.D., J. Weiss-Lerman, L.R. Erickson, and V. Souza Machado (1980). Transfer of cytoplasmically-inherited triazine resistance from bird s rape to cultivated oilseed rape (Brassica campestris and B. napus). Can. J. Genet. Cytol., 22 167-172. 

Beversdorf, W.D., D.J. Hume, and M.J. Donnelly-Vanderloo (1988). Agronomic performance of triazine-resistant and susceptible reciprocal spring canola hybrids. Crop Sci., 28 932-934. 

Burke, J.J., R.F. Wilson, and J.R. Swafford (1982). Characterization of chloroplasts isolated from triazine-susceptible and triazine-resistant biotypes of Brassica campestris L. Plant Physiol., 70 24—29. 

Fuerst, E.P., C.J. Arntzen, K. Pfister, and D. Penner (1986). Herbicide cross-resistance in triazine-resistant biotypes of four species. Weed Sci., 34 344-353. 

Grant, I. and W.D. Beversdorf (1985). Agronomic performance of triazine-resistant single-cross hybrid oilseed rape (Brassica napus L.). Can. J. Plant Sci., 65 889-892. 

Hall, J.C., M.J. Donnelly-Vanderloo, and D.J. Hume (1996). Triazine-resistant crops The agronomic impact and physiological consequences, pp. 107-126. In Duke, S.O. ed., Herbicide-Resistant Crops. Boca Raton, FL Lewis Publishers. 

Hart, J.J. and A. Stemler (1990). High light-induced reduction and low light-enhanced recovery of photon yield in triazine-resistant Brassica napus L. Plant Physiol., 94 1301-1307. 

Jansen, M.A.K. and K. Pfister (1990). Conserved kinetics at the reducing side of reaction-center II in photosynthetic organisms changed kinetics in triazine-resistant weeds. Z. Naturforsch., 45c 441 -45. 

Ritter, R.L. (1986). Triazine resistant velvetleaf and giant foxtail control in no-tillage corn. Proc. Northeast Weed Sci. Soc., 40 50-52. 

Stephenson, G.R., M.D. Dykstra, R.D. McLaren, and A.S. Hamill (1990). Agronomic practices influencing triazine-resistant weed distribution in Ontario. Weed Technol., 4 199-207. 

Vaughn, K.C. (1986). Characterization of triazine-resistant and susceptible isolines of canola (Brassica napus L.). Plant Physiol., 82 859-863. 

Soon after the discovery of triazine-resistant common groundsel, another equally important discovery was made. Radosevich and DeVilliers (1976) found that the mechanism of resistance in this weed was due to insensitive chloro-plasts that were capable of photosynthesis, even in the presence of simazine or atrazine. This was surprising because earlier research had confirmed that there were no differences in plant selectivity or susceptibility due to the origin of chloroplasts. Moreland (1969) had reported that isolated chloroplasts were equally inhibited to simazine whether they came from tolerant com or susceptible spinach. Radosevich and Appleby (1973) had confirmed there were no differences between the susceptible and resistant biotypes of common groundsel due to herbicide uptake, distribution, or metabolism, whereas it is known that com metabolizes triazine herbicides (Shimabukuro, 1985). 

Within North America and a few other countries, most triazine-resistant weed biotypes have been reported after repeated use of atrazine in com and sorghum. In some areas of Western Europe and other countries, triazine-resistant weeds have been reported after repeated use of simazine in orchards and along roadsides. A few triazine-resistant weeds (e.g., kochia, cheatgrass, and common groundsel) have biotypes with triazine resistance in nurseries and perennial tree crops, as well as along railways and roadsides. 

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