A decade of herbicide-resistant crops in Canada

Non-Peer ReviewedThis review examines some agronomic, economic, and environmental impacts of herbicide-resistant (HR) canola, soybean, corn, and wheat in Canada after 10 years of growing HR cultivars. The rapid adoption of HR canola and soybean suggests a net economic benefit to farmers. HR crops often have improved weed management, greater yields or economic returns, and similar or reduced environmental impact compared with their non-HR crop counterparts. There are no marked changes in volunteer weed problems associated with these crops, except in zero-tillage systems when glyphosate is used alone to control canola volunteers. Although gene flow from glyphosate-HR canola to indigenous populations of bird’s rape in eastern Canada has been measured, enrichment of hybrid plants in such populations should only occur when and where herbicide selection pressure is applied. Weed shifts as a consequence of HR canola have been documented, but a reduction in weed species diversity has not been demonstrated. Reliance on HR crops in rotations using the same mode-of-action-herbicide and/or multiple in-crop herbicide applications over time can result in intense selection pressure for weed resistance and consequently, greater herbicide use in the future to control HR weed biotypes. History has repeatedly shown that cropping system diversity is the pillar of sustainable agriculture; stewardship of HR crops must adhere to this fundamental principle

Genetic load and transgenic mitigating genes in transgenic Brassica rapa (field mustard) × Brassica napus (oilseed rape) hybrid populations

<p>Abstract</p> <p>Background</p> <p>One theoretical explanation for the relatively poor performance of <it>Brassica rapa </it>(weed) × <it>Brassica napus </it>(crop) transgenic hybrids suggests that hybridization imparts a negative genetic load. Consequently, in hybrids genetic load could overshadow any benefits of fitness enhancing transgenes and become the limiting factor in transgenic hybrid persistence. Two types of genetic load were analyzed in this study: random/linkage-derived genetic load, and directly incorporated genetic load using a transgenic mitigation (TM) strategy. In order to measure the effects of random genetic load, hybrid productivity (seed yield and biomass) was correlated with crop- and weed-specific AFLP genomic markers. This portion of the study was designed to answer whether or not weed × transgenic crop hybrids possessing more crop genes were less competitive than hybrids containing fewer crop genes. The effects of directly incorporated genetic load (TM) were analyzed through transgene persistence data. TM strategies are proposed to decrease transgene persistence if gene flow and subsequent transgene introgression to a wild host were to occur.</p> <p>Results</p> <p>In the absence of interspecific competition, transgenic weed × crop hybrids benefited from having more crop-specific alleles. There was a positive correlation between performance and number of <it>B. napus </it>crop-specific AFLP markers [seed yield vs. marker number (r = 0.54, P = 0.0003) and vegetative dry biomass vs. marker number (r = 0.44, P = 0.005)]. However under interspecific competition with wheat or more weed-like conditions (i.e. representing a situation where hybrid plants emerge as volunteer weeds in subsequent cropping systems), there was a positive correlation between the number of <it>B. rapa </it>weed-specific AFLP markers and seed yield (r = 0.70, P = 0.0001), although no such correlation was detected for vegetative biomass. When genetic load was directly incorporated into the hybrid genome, by inserting a fitness-mitigating dwarfing gene that that is beneficial for crops but deleterious for weeds (a transgene mitigation measure), there was a dramatic decrease in the number of transgenic hybrid progeny persisting in the population.</p> <p>Conclusion</p> <p>The effects of genetic load of crop and in some situations, weed alleles might be beneficial under certain environmental conditions. However, when genetic load was directly incorporated into transgenic events, e.g., using a TM construct, the number of transgenic hybrids and persistence in weedy genomic backgrounds was significantly decreased.</p

Identification of farm management systems at risk for ACCase inhibitor-resistant wild oat (Avena fatua L.)

Non-Peer Reviewe

Early development od individual lambsquarters (Chenopodium album L.) and yellow foxtail (Setaria glauca (L.) Beauv.) plants from-cultivation cohorts

International audienc

Simple parameters available for decision support system in maize under postemergence weed management programs

National audienc

A new method to study weed competition for light in corn

International audienc

What is the cost to manage herbicide-resistant wild oat and green foxtail?

Non-Peer Reviewe