Abstract
Overreliance on herbicides for weed control is conducive to the evolution of herbicide resistance. Lolium rigidum (annual ryegrass) is a species that is prone to evolve resistance to a wide range of herbicide modes of action. Rapid detection of herbicide-resistant weed populations in the field can aid farmers to optimize the use of effective herbicides for their control. The feasibility and utility of a rapid 7-d agar-based assay to reliably detect L. rigidum resistant to key pre- and post-emergence herbicides including clethodim, glyphosate, pyroxasulfone and trifluralin were investigated in three phases: correlation with traditional pot-based dose-response assays, effect of seed dormancy, and stability of herbicides in agar. Easy-to-interpret results were obtained using non-dormant seeds from susceptible and resistant populations, and resistance was detected similarly as pot-based assays. However, the test is not suitable for trifluralin because of instability in agar as measured over a 10-d period, as well as freshly-harvested seeds due to primary dormancy. This study demonstrates the utility of a portable and rapid assay that allows for on-farm testing of clethodim, glyphosate, and pyroxasulfone resistance in L. rigidum, thereby aiding the identification and implementation of effective herbicide control options.
Highlights
The aim of this study was to develop and evaluate an easy-to-interpret on-farm test to rapidly detect resistance in L. rigidum populations to key pre- and postemergence herbicides used in Australian grain cropping: clethodim, an acetyl-CoA carboxylase inhibitor; glyphosate, a 5-enolpyruvylshikimate-3-phosphate synthase inhibitor; pyroxasulfone, a very long chain fatty acid elongase inhibitor; and trifluralin, a cell division inhibitor
(0.075–0.15 μM) resulted in 2% to 20% survival of the pyroxasulfone-resistant populations (Figure 2C), whereas survival to trifluralin applied from 10 to 50 μM was relatively high in both trifluralin-resistant populations, ranging between 10% and 60% (Figure 2D)
Using an test prepared pot-based assays for herbicide resistance of L. rigidum to agar-based key pre- and postin theherbicides laboratory, it would be used distributed to growers their service emergence that could be on-farm
Summary
Since the 1880s, highly adaptable Lolium rigidum Gaud. After a substantial shift towards annual cropping in the 1950s, the control of L. rigidum infestations became a priority in cereals, oilseeds, and pulses because of the highly competitive and economically damaging nature of the weed even at early developmental stages [2]. Weeds such as L. rigidum are a major constraint for Australian farming systems; the financial cost from yield loss and weed control expenditure amounts to AU $3.3 billion per year [3]
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