Lolium rigidum, herbicide resistance

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

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. 

Christopher, J.T., S.B. Powles, and J.A.M. Holtum (1992). Resistance to acetolactate synthase-inhibiting herbicides in annual ryegrass (Lolium rigidum) involves at least two mechanisms. Plant Physiol., 100 1909-1913. 

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. 

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 ... 

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]. 

The frequent use of AOPP and CHD graminicides has resulted in the development of resistance to these herbicides in some grass species throughout the world [33]. Up to now, 35 resistant species [34] have been reported. The species in which resistance has developed include the important grass weeds Alopecurus myosuroides, Avena fatua, Setaria viridis, S. faheri, Lolium rigidum and Eleusine indica. 

Diclofop-methyl is widely used in Australia to control Lolium rigidum (annual ryegrass) both in broadleaf crops and in wheat. This Lolium weed is often cultivated there as a pasture grass in rotation with wheat and other crops, guaranteeing a huge reservoir of seeds from which to select resistance. A loss of control of diclofop-methyl was reported a few years ago in one population [22]. Since then, resistance has concurrently evolved in innumerable foci in four Australian states. Resistance is characterized by a simultaneous cross resistance to wheat herbicides that previously controlled it, and to other herbicides that damage wheat (Table 2). There are some differences in the quantitative levels of cross resistances in the Aus-... 

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