The evolutionary response of wild radish (Raphanus raphanistrum L.) populations to selections in agriculture

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    [Truncated] Herbicide-resistant weeds pose a significant threat to the sustainability of global grain production. Of all weeds in Australian farming systems, wild radish (Raphanus raphanistrum L.) is one of the most economically damaging, aggressively competing for water, nutrients and light. As a result of herbicide over-reliance, wild radish populations in the Western Australian (WA) grainbelt have evolved multiple resistances to inhibitors of acetolactate synthase (ALS), phytoene desaturase (PDS), photosynthetic electron transport (PSII) and synthetic auxin herbicides.
    However, following 40 years of over-reliance on glyphosate, this PhD study is the first to report glyphosate resistance in wild radish. Two wild radish populations from fallow fields near Mingenew and Carnamah in the WA grainbelt exhibited a heritable, 3.2 (WARR37) and 4.5 (WARR38) fold resistance (LD50) to glyphosate. Both populations also had multiple resistances to ALS inhibitors, PDS inhibitors and synthetic auxin herbicides, which is expected to intensify the selection for glyphosate resistance in these populations.
    The inspection of 24,000 ha of the first commercial transgenic glyphosate-resistant (GR) canola plantings in the WA grainbelt (2010–2011) found large wild radish populations treated solely with glyphosate, which often resulted in less than complete control. Glyphosate resistance in wild radish however was rare, with only one additional GR population identified. This survey also identified glyphosate resistance in eight annual ryegrass (Lolium rigidum L.) populations. However no glyphosate resistance was identified in barley grass species (Hordeum sp.), brome grass species (Bromus sp.), wild oat species (Avena sp.), capeweed (Arctotheca calendula L.) and mallow (Malvia parviflora L.).
    The less than complete control of wild radish in the first GR canola crops grown in the WA grainbelt was of concern, as four generations of glyphosate selection at rates that do not provide full control, resulted in modest increases in glyphosate resistance (2.4-fold). Additionally this selection also resulted in weak cross resistance to the ALS-inhibiting herbicides imazamox (4.7-fold) and metosulam (3.7-fold). The biochemical basis of this weak resistance remains to be investigated.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Publication statusUnpublished - Feb 2015


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