Multiple herbicide resistance

Sibony, M. and B. Rubin (2004). Molecular basis for diverse level of herbicide multiple-resistance in prostrate pigweed (Amaranthus blitoides). 4th International Weed Science Congress, p. 53, S15MT08P00. 

Hall, L., Topinka, K., Huffman, J., Davis, L. and Good, A. (2000). Pollen flow between herbicide-resistant Brassica napus is the cause of multiple-resistant B. napus volunteers. Weed Sci, 48, 688-694. 

Multiple-resistance is when more than one mechanism conferring resistance to herbicides in different chemical classes is active in an individual weed or population of weeds. Plants with multiple resistance may possess two or more distinct resistance mechanisms. Two grass species that display both cross- and multiple-resistance are rigid (or annual) ryegrass and blackgrass (Hall et al., 1994). 

Until the mid-1990s, multiple-resistance (i.e., resistance to more than one herbicide mode of action within the same biotype) had not been reported within North America. However, Foes et al. (1996) found a kochia biotype from western Illinois resistant to atrazine and several ALS-inhibiting herbicides. Lopez-Martinez et al. (1996) reported that a triazine-resistant Echinochloa species found in atrazine-treated com also showed cross-resistance to quinclorac. Clay and Underwood (1989) and Clay (1989) reported that one triazine-resistant biotype of American willowherb was also resistant to paraquat from a hop garden in the United Kingdom treated annually for 25 years with simazine and paraquat. 

Foes et al. (1998) reported that a common waterhemp biotype not controlled by triazine or ALS-inhibiting herbicides was isolated from a field in Illinois in the fall of 1996. Patzoldt et al. (2004, 2005) have reported on a tall waterhemp biotype in Illinois that has multiple resistance to ALS inhibitors, PPO inhibitors, and atrazine in the same plants. Maertens et al. (2004) reported a smooth pigweed biotype from southern Illinois confirming multiple resistance to both atrazine and ALS inhibitors. 

Hall, L.M., J.A.M. Holtum, and S.B. Powles (1994). Mechanisms responsible for cross resistance and multiple resistance. In S.B. Powles and J.A.M. Holtum, eds., Herbicide Resistance in Plants Biology and Biochemistry. Boca Raton, Florida CRC Press, pp. 243-261. 

Patzoldt, W.L., P.J. Tranel, and A.G. Hager (2005). A waterhemp (Amaranthus tuberculatus) biotype with multiple resistance across three herbicide sites of action. Weed Sci., 53 30-36. 

Multiple Herbicide Class Resistances in ALS-Resistant Biotypes... 

Multiple-resistance mechanisms, defined as resistance due to more than one mode of action or class of herbicide, have been reported in several ALS-resistant weed biotypes - including false cleavers, wild oat, common waterhemp, kochia, rigid ryegrass in Australia (Powles and Matthews, 1992 Preston and Mallory-Smith, 2001), and wild radish (Walsh etal, 2004a). 

Diebold et al. (2003) concluded that multiple resistance in a Powell amaranth biotype in Ontario was due to the presence of altered target sites for triazine and imidazolinone herbicides. 

Hall et al. (1998) reported that an ALS-resistant biotype of false cleavers was cross-resistant to a broad range of ALS inhibitors, as well as to an auxin-type herbicide, quinclorac, which had never before been applied to these fields. A similar case of quinclorac multiple resistance in smooth crabgrass has been reported in California when plants were previously treated with ACCase herbicides. Data suggest a target site-based mechanism of resistance involving the accumulation of cyanide derived from stimulated ACC synthesis, which is a precursor of ethylene (Abdallah et al., 2004). 

Adapted species may have developed, however, strategies which enable them to survive allelopathic attacks. One of those strategies certainly includes detoxification of absorbed allelochemicals by constitutive or inducible pathways. Metabolization and detoxification are known reactions in a number of crops upon application of diverse synthetic herbicides.38 Enhanced herbicide detoxification is an important factor in the development of nontarget-site cross-resistance and multiple resistance. It is reasonable to expect comparable strategies in plants that are relatively resistant to allelochemicals such as DIBOA, DIMBOA, and their derivatives. Especially in ecosystems where co-existing species have to be adapted to each other, detoxification of absorbed allelochemicals may play a crucial role under defined circumstances. 

The lower relative fitness in most triazine resistant weeds is a very important reason why they have been fairly easily controlled, and why more problems of cross-resistance or multiple resistance have not occurred where both a triazine and another type of herbicide have been used together repeatedly. However, some cases of such cross-resistance are now beginning to appear, consistent with the predictions by Gressel and Segel (12). 

It is not yet clear whether such factors will delay the rate of appearance of other types of resistance e.g. the multiple resistances to grass-killing herbicides in wheat, or to inhibitors of acetolactate synthase, where the fitness of resistant biotypes may be higher. 

Selection of multiple resistance after sequential use of different herbicides has been described for a biotype of Kochia scoparia from North America. Many years... 

Obviously, multiple resistance leads to complex patterns of broad herbicide resistance, particularly in cross-pollinating weed species. This seriously restricts the remaining options of chemical weed control in agricultural practice. 

Herbicide group Site of Action Multiple resistance... 

A few populations of Abutilon theophrasti have evolved resistance to triazine herbicides as a result of increased GST conjugation of the herbicide. One resistant population has an increase in GST with specific action against atrazine 23). It has also been suggested that multiple resistance in Alopecurus myosuroides may involve an increase in GST acting as glutathione peroxidase 24). 

According to the International Survey of Herbicide Resistant Weeds (www. weedscience.org) report, there are currentiy 434 imique cases of herbicide resistant weeds globally, involving 237 species (138 dicots and 99 monocots). Herbicide resistant weeds have been reported in 82 crops in 65 coimtries. Multiple resistances also have been observed. Weeds have evolved resistance to 22 of the 25 known herbicide sites of action and to 155 different herbicides. The evolution of herbicide-resistant weeds for selected herbicides of six leading sites of actions is shown in Table 1.4. 

Powles, S.B. and J.M. Matthews. (1992) Multiple herbicide resistance in annual rye grass (Lolium rigidum) A driving force for the adaption of integrated weed management. In L. Denholin, A. Devonshire, and D. Holloman, eds., Achievements and Developments in Combating Pest Resistance. London, UK Elsevier Press, pp. 1-13. 

Walsh, M.J., S.B. Powles, B.R. Beard, B.T. Parkin, and S.A. Porter (2004). Multiple-herbicide resistance across four modes of action in wild radish (Raphanus). Weed Sci., 52 8-13. 

Neve, P, J. Sadler, and S.B. Powles (2004). Multiple herbicide resistance in a glyphosate-resistant rigid ryegrass (Lolium rigidum) population. Weed Sci. 52 920-928. 

Triazine herbicides provide cost-effective, broad-spectrum weed control and are key tools in conservation tillage. Although the chemical alternatives to the triazines are more costly and generally less efficacious, they are considerably more reliable as weed control methods and more compatible with current farming operations than available nonchemical weed control methods. Even as more com acreage shifts to herbicide-tolerant com, the need remains for residual herbicides such as the triazines to manage resistant weeds and to avoid the need for multiple tillage passes for weed control. 

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