Chlorsulfuron resistance

Christopher et al. (1992) reported that a chlorsulfuron-resistant rigid ryegrass in Australia was resistant to most other sulfonylurea and imidazolinone ALS inhibitors. However, a common cocklebur biotype resistant to several imida-zolinone herbicides was not resistant to sulfonylurea herbicides (Saari et al., 1994). It is, therefore, difficult to generalize as to patterns of resistance within the five classes of ALS inhibitors. Weed biotypes resistant to one herbicide will usually show some level of resistance to most herbicides within the same class, and may in addition show some resistance to ALS inhibitors in other classes. 

Devine et al. (1991) and O Donovan et al. (1994) reported that chlorsulfuron-resistant chickweed populations were also resistant to other sulfonylurea herbicides. Primiani et al. (1990) reported cross-resistance to several sulfonylurea and imidazolinone herbicides in chlorsulfuron-resistant kochia. Lovell et al. (1996a) also documented that chlorsulfuron-resistant kochia biotypes from Idaho and Montana were cross-resistant to imazethapyr. 

Boutsalis, P. (2001). Herbicide Resistance Action Committee (HRAC) Web page http //plantprotection.org/HRAC Bradshaw, L.D., S.R. Padgette, S.L. Kimball, and B.H. Wells (1997). Perspectives on glyphosate resistance. Weed Technol., 11 189-198. Bravin, F., A. Onofri, G. Zanin, and M. Sattin (2004). Is malathion a useful tool to infer the chlorsulfuron-resistance mechanism in mul-tiresistant Italian populations of Lolium spp. 4th International Weed Science Congress, p. 52, S15MT08P00. 

Christopher, J.T., S.B. Powles, J.A.M. Holtum, and D.R. Liljegren (1991). Cross-resistance to herbicides in annual ryegrass (Lolium rigi-dum) II Chlorsulfuron resistance involves a wheat-like detoxification system. Plant Physiol., 100 1036-1043. 

Hall, L.M. and M.D. Devine (1990). Cross-resistance of a chlorsulfuron-resistant biotype of Stellaria media to a triazolopyrimidine herbicide. Plant Physiol., 93 962-966. 

Walsh, M.J., R.D. Duane, and S.B. Powles (2001). High frequency of chlorsulfuron-resistant wild radish (Raphanus raphanistrum) populations across the Western Australian wheatbelt. Weed Technol., 15 199-203. 

The negative cross-resistances in atrazine-resistant weeds include herbicides that act at or near the same site in photosystem II (DNOC and dinoseb) as well as herbicides acting on other photosystems (paraquat) or at totally different sites. There was negative cross-resistance to other tubulin binding herbicides in dinitroaniline resistant Eleucine indica (Table II), but not to six commercial herbicides on this weed (12). The negative cross-resistance to imazaquin (Table II) occurred in only one of 21 chlorsulfuron resistant mutants. The other mutants had varying levels of co-resistance to imazaquin. 

Assuming that the chlorsulfuron resistance In the A. thallana mutants described here Is due to a mutation within the ALS structural locus. It may be possible to clone the resistant allele. Such a resistance gene should provide a very useful selectable marker for plant transformation studies. Indeed, transfer of the gene to other species may be useful In extending the agronomic utility of the herbicide. 

The first ALS-resistant weeds were reported in 1987 when prickly lettuce (Mallory-Smith, 1990 Mallory-Smith et al, 1990b) and kochia (Primiani et al, 1990) control failures occurred in Idaho and Kansas, respectively, after 5 consecutive years of chlorsulfuron use. The kochia biotype proved to be cross-resistant to six other ALS-inhibitor herbicides, including sulfonylureas and imidazolinones. Within 5 years, sulfonylurea-resistant kochia had been identified at 832 sites in 11 states of the United States and in three Canadian provinces (Saari et al, 1994). ALS inhibitor-resistant kochia and Russian thistle have become widespread problems in cereal-producing regions of northwestern United States and Canada. The mobility of these tumble weeds as plants with mature seeds or pollen carried by wind has undoubtedly contributed to the rate at which resistance has spread. 

Numerous cases of resistance to the ALS inhibitors have now been reported in other broadleaf weed species, including pigweed and cocklebur, as well as grasses such as shattercane. Walsh et al. (2001) reported that only a few years after the first case of ALS-resistant wild radish, a major weed in Australian wheat fields, 21% of randomly collected wild radish populations were found to be resistant to chlorsulfuron. Patzoldt and Tranel (2002) reported that cloransulam resistance was found in an Indiana population of giant ragweed during the first year of that herbicide s commercialization in 1998, and that the resistant plants were cross-resistant to imazethapyr and chlorimuron. Since 1989, the number of species resistant to ALS inhibitors has increased almost 10-fold in crops and on roadsides. The total ALS-resistant weed species now number 108, as seen in Tables 11.4a and b). 

In 2001, Llewellyn and Powles reported a survey of fields in the Western Australian Wheat Belt, conducted to determine the extent of rigid ryegrass resistance to commonly used herbicides (i.e., diclofop-methyl, clethodim, chlorsulfuron, and sulfometuron). Of the randomly collected populations, 46% exhibited resistance to diclofop-methyl and 64% to chlorsulfuron, with 37% exhibiting resistance to both herbicides. 

In 1987, Moss first reported that a blackgrass biotype resistant to chlorotoluron and isoproturon (urea herbicides in WSSA Group 7) was also resistant to the ALS inhibitor chlorsulfuron. Menendez el al. (1997) also found that a chlorotoluron-resistant blackgrass biotype in Spain was resistant to ALS inhibitors (e.g., chlorsulfuron and imaza-methabenz), and that the resistance was due to its greater ability to metabolize the herbicides. 

Cotterman, J.C. and F.F. Saari (1992). Rapid metabolic inactivation is the basis for cross-resistance to chlorsulfuron in diclofop-methyl-resistant rigid ryegrass (Lolium rigidum) biotype SR4/84. Pestic. Biochem. Physiol., 43 182-192. 

Menendez, J.M., R. De Prado, and M.D. Devine (1997). Chlorsulfuron cross-resistance in a chlorotoluron-resistant biotype of Alopecurus myosuroides. Brighton Crop Protection Conference-Weeds, 319-324. 

It is known that wheat, a resistant species degrades chlorsulfuron (16, 17) so it can be expected that some weeds do the same, but at a lower rate. 

ACC was extracted from hydroponically-grown susceptible and resistant biotypes of Lolium. The extracts were subjected to (NH)2S04 fractionation followed by gel filtration. The ATP-, acetyl Co-A- and protein- dependent incorporation of radioactivity from H14C03 into acid-stable products was monitored. The sensitivity of ACC from both biotypes to diclofop-methyl, diclofop-acid, fluazifop-acid, sethoxydim and tralkoxydim was similar (Table I). The small differences observed are unlikely to account for resistance at the whole plant level. ACC was not affected by either chlorsulfuron or trifluralin, two herbicides against which there is resistance but which have different modes of action. 

Lolium biotypes exist which have resistance to the sulfonylurea herbicides chlorsulfuron and metsulfuron methyl (4). The biotype used in the studies presented here is resistant to both these sulfonylurea herbicides. Sulfonylurea herbicides inhibit the chloroplastic enzyme acetolactate synthase (ALS), also known as acetohydroxyacid synthase (AHAS) (16). Inhibition of this enzyme results in disruption of the synthesis of the branched-chain amino acids valine and isoleucine (161. The imidazolinone herbicides also inhibit ALS Q2). In some species auxins can protect against chlorsulfuron inhibition (S. Frear, USDA North Dakota, personal communication) the mechanistic basis for this protection is not known. We have measured the ALS activity in the resistant and susceptible Lolium and have also checked for any induction of ALS activity following treatment with the sulfonylurea herbicide chlorsulfuron. 

Figure 3. Effect of chlorsulfuron on acetolactate synthase (ALS) activity in extracts from leaves of resistant (A) and susceptible (B) Lolium rigidum. ALS was extracted from plants following 7-8 days growth in nutrient solution in the presence ( ) or absence (O) of 100 nM chlorsulfuron.

---