Measurement and modelling of herbicide resistance evolution in 'Lolium rigidum' at low rates of herbicide application

    Research output: ThesisDoctoral Thesis

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    [Truncated abstract] Herbicides help the world to meet its ever-increasing demand for food, fibre and fuel. However, the intensive use of herbicides has led to the evolution of herbicide resistant weeds. Of these resistant weeds, some represent long-term problems in many agro-climatic regions across the world. Lolium rigidum Gaud. (annual ryegrass) is an example of such a major herbicide resistant weed. The cross-pollinating L. rigidum possess many biological and genetic attributes that ensure its success as an ever evolving resistant weed. Besides, there can be operational factors that decide the pace of resistance evolution of which herbicide use rate is a major determinant. Herbicides at the recommended rates ensure high weed mortality. Whenever the same herbicide is used intensively, resistant weed populations evolve often due to the selection of major gene herbicide resistance traits. However, recent laboratory studies indicate the potential of low herbicide rates to result in rapid herbicide resistance evolution in L. rigidum due to the selection of minor gene resistance traits. Until now a crop-field study on whether the reduced herbicide rates that prevail on farms can lead to resistance evolution in L. rigidum, has been lacking. Therefore, this study examined the impact of low rates of diclofop-methyl (ACCase herbicide) on the evolution of herbicide resistance in a herbicide-susceptible L. rigidum population grown either in a field wheat crop or in potted plants maintained in the field. The results established the rapid evolution of diclofop-methyl resistance in both the crop-field and field pot studies in the selected L. rigidum lines. In addition, there was resistance evolution in the selected lines to other herbicides to which the population had never been exposed. For the first time, we demonstrated the potential of a low rates of diclofop-methyl to result in the evolution of diclofop-resistance and cross-resistance in L. rigidum under crop-field
    Original languageEnglish
    QualificationDoctor of Philosophy
    Publication statusUnpublished - 2010


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