Lolium, herbicide resistance

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. 

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. 

Llewellyn, R.S. and S.B. Powles (2001). High levels of herbicide resistance in rigid ryegrass (Lolium rigidum) in the wheat belt of Western Australia. Weed Technol., 15 242-248. 

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. 

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. 

Perez-Jones, A. and C. Mallory-Smith (2004). Resistance of Italian ryegrass (Lolium multiflorum) to acelolactate synthase inhibiting herbicides in Oregon. Weed Sci. Soc. Am. Abstr., 44 81. 

Richter, J. and S.B. Powles (1993). Pollen expression of herbicide target site resistance genes in annual ryegrass (Lolium rigidum). Plant Physiol., 102 1037-1041. 

Herbicide Cross-Resistance in Annual Ryegrass (Lolium rigidum Gaud)... 

An understanding of the mechanistic basis of cross-resistance in Lolium rigidum requires recognition of the fact that the plants are resistant to herbicides which act differently within the plant. Any mechanism, or mechanisms, of resistance must therefore be general enough to account for the resistance to a number of dissimilar herbicides, yet specific enough to account for the herbicide susceptibility that is still observed. There are at least five general, not necessarily mutually exclusive, mechanisms which could account for cross-resistance ... 

Figure 1. Examples of structurally distinct herbicides against which biotypes of Lolium rigidum are resistant.

Diclofop-methyl is a herbicide which, upon entry into the plant, undergoes minimal acropetal and basipetal transport (8). In our experiments transport to the roots or to the leaves of [14C] diclofop-methyl applied to the axils of two-leaved susceptible and resistant Lolium plants does not appear to differ. No data are presently available as to whether proplastids or chloroplasts from the two biotypes exhibit differential permeability to diclofop-methyl or to the active acid derivative diclofop. Similarly, there is no evidence for a differential capacity to convert diclofop-methyl to diclofop nor differential sequestration of the ester or the acid in some secondary compartment such as the vacuole or within membranes. 

REDUCTION IN THE SENSITIVITY OF HERBICIDE TARGET SITES. Crossresistance may involve changes in the sensitivity of herbicide target sites. However, if this is the only mechanism for resistance in Lolium there must be changes in more than one target site since there is resistance to more than one herbicide class. 

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. 

We conclude that, in Lolium, neither intrinsic nor induced differences in the amounts or the characteristics of ACC are responsible for cross-resistance to the aryloxyphenoxy-propionate and cyclohexanedione herbicides. 

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. 

In considering whether MFO-catalyzed metabolism of herbicides is associated with cross-resistance in Lolium rigidum we have taken, initially, an indirect approach. Growth experiments with wheat showed that the MFO inhibitors aminobenzotriazole (ABT) and PBO synergized chlortoluron when the herbicide and inhibitors were added as a soil drench (34). This synergism was presumed to be due to the inhibition of MFO-catalysed metabolism of chlortoluron (27-29). Significantly, Kemp and Caseley (2) have shown that cross-resistant Alopecurus are relatively more susceptible to chlortoluron in the presence of ABT and other... 

The mixed-function oxidase inhibitors aminobenzotriazole and piperonyl butoxide can synergize herbicide activity in resistant Lolium growing in a hydroponic system. This indicates that at least one aspect of cross-resistance in Lolium rigidum may be related to enhanced metabolic activity of mixed-function oxidazes acting to detoxify herbicides. We are now concentrating on direct studies of herbicide metabolism in resistant biotypes. 

Burnet, M.W.M., Hart, Q., Holtum, J.A.M., and Powles, S.B. 1994b. Resistance to 9 herbicide classes in a population of rigid ryegrass (Lolium-rigidum). Weed Sci.,... 

Resistant biotypes being reported in the early 1990s were selected by chlorsul-furon or metsulfuron-methyl in wheat-growing areas or by sulfometuron-methyl in non-crop areas. While resistance of Lolium rigidum to ALS-inhibitors was attributed to enhanced herbicide metabolism [50] it was shown, for Lolium perenne and dicotyledonous species like Stellaria media, Kochia scoparia, Scdsola iberica and Lactuca serriola, that resistant biotypes had a mutated ALS with reduced susceptibility to ALS-inhibitmg herbicides [51-53]. The IC50S for sulfonylureas, which were determined in vitro with ALS isolated from Stellaria media, Salsola iberica and Lolium perenne, increased 4- to 50-fold in the resistant biotypes. Smaller increases, about 2- to 7-fold, were determined in the same biotypes for the imidazo-linone herbicide imazapyr [53]. 

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