The frequency of gene flow from Brassica napus L. (canola) to four wild relatives, Brassica rapa L., Raphanus raphanistrum L., Sinapis arvensis L. and Erucastrum gallicum (Willd.) O.E. Schulz, was assessed in greenhouse and/or field experiments, and actual rates measured in commercial fields in Canada. Various marker systems were used to detect hybrid individuals: herbicide resistance traits (HR), green fluorescent protein marker (GFP), species-specific amplified fragment length polymorphisms (AFLPs) and ploidy level. Hybridization between B. rapa and B. napus occurred in two field experiments (frequency approximately 7%) and in wild populations in commercial fields (approximately 13.6%). The higher frequency in commercial fields was most likely due to greater distance between B. rapa plants. All F(1) hybrids were morphologically similar to B. rapa, had B. napus- and B. rapa-specific AFLP markers and were triploid (AAC, 2n=29 chromosomes). They had reduced pollen viability (about 55%) and segregated for both self-incompatible and self-compatible individuals (the latter being a B. napus trait). In contrast, gene flow between R. raphanistrum and B. napus was very rare. A single R. raphanistrum x B. napus F1 hybrid was detected in 32,821 seedlings from the HR B. napus field experiment. The hybrid was morphologically similar to R. raphanistrum except for the presence of valves, a B. napus trait, in the distorted seed pods. It had a genomic structure consistent with the fusion of an unreduced gamete of R. raphanistrum and a reduced gamete of B. napus (RrRrAC, 2n=37), both B. napus- and R. raphanistrum-specific AFLP markers, and had <1% pollen viability. No hybrids were detected in the greenhouse experiments (1,534 seedlings), the GFP field experiment (4,059 seedlings) or in commercial fields in Québec and Alberta (22,114 seedlings). No S. arvensis or E. gallicum x B. napus hybrids were detected (42,828 and 21,841 seedlings, respectively) from commercial fields in Saskatchewan. These findings suggest that the probability of gene flow from transgenic B. napus to R. raphanistrum, S. arvensis or E. gallicum is very low (<2-5 x 10(-5)). However, transgenes can disperse in the environment via wild B. rapa in eastern Canada and possibly via commercial B. rapa volunteers in western Canada.

Multiple herbicide resistance to glyphosate, glufosinate, bromoxynil, or imidazolinone in volunteer plants of canola (Brassica napus) has been attributed to pollen flow among cultivars with different resistance traits. A study was conducted in Saskatchewan, Canada, in 1999 and to assess gene flow in space and time in adjacent commercial fields of glyphosate-and glufosinate-resistant canola, including (1) estimation of gene flow with distance; (2) frequency and distribution of volunteers, and effect on gene flow; (3) effect of adventitious double herbicide-resistant seed presence in seedlots planted; and (4) a comparison of various marker systems to track gene flow events. At 11 sites in 1999, gene flow was determined by sampling seeds from plants located at 0, 50, 100, 200, 400, 600, or 800 m along a transect perpendicular to the common border in the paired fields, spraying seedlings with glyphosate and glufosinate, and confirming the presence of the transgenes using commercial test strips and PCR analysis. In the spring of 2000, putative double herbicide-resistant volunteers that survived sequential herbicide applications were mapped at three of the sites using GPS and resistance in sampled plants was characterized. In 1999, gene flow between the paired fields was detected to a maximum distance of 400 m. Values ranged from 1.4% outcrossing at the border common to the paired fields to 0.04% at 400 m. In 2000, gene flow as a result of pollen flow in 1999 was detected to the limits of the study areas (800 m). Large variation in gene flow levels and patterns among the three sites was evident. Adventitious presence of double herbicide-resistant seed in glyphosate-resistant seedlots planted at two of the sites in 1999 contributed to the occurrence of double herbicide-resistant volunteers in 2000. The results of this study suggest that gene stacking in B. napus canola volunteers in western Canada may be common, and reflects pollen flow between different herbicide-resistant canola, presence of double herbicideresistant off-types in seedlots, and/or agronomic practices typically employed by Canadian growers.

-J. 2006. A decade of herbicide-resistant crops in Canada. Can. J. Plant Sci. 86: 1243-1264. This review examines some agronomic, economic, and environmental impacts of herbicide-resistant (HR) canola, soybean, corn, and wheat in Canada after 10 yr 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 wild populations of bird's rape (Brassica rapa L.) 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. However, 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. L'adoption rapide du canola et du soja RH laisse croire que les agriculteurs y trouvent un net avantage économique. Les cultures RH ont souvent facilité la lutte contre les mauvaises herbes, accru le rendement ou les revenus tout en ayant un impact similaire voire plus faible que les cultures qui ne le sont pas sur l'environnement. On ne remarque pas de changement marqué au niveau de la repousse spontanée des adventices avec ces cultures, sauf dans les systèmes de non-travail du sol où l'on n'utilise que du glyphosate pour combattre la repousse spontanée du canola. Bien qu'on ait mesuré la transmission de gènes du canola résistant au glyphosate aux populations sauvages de navette (Brassica rapa L.) dans l'est du Canada, l'enrichissement de ces populations par des hybrides ne survient que si l'herbicide accentue la pression sélective. La littérature scientifique cite des cas où la population d'adventices change consécutivement à la culture de canola RH, mais on n'a pu démontrer l'appauvrissement de la diversité des espèces. Employer des cultures RH dans les assolements où l'on recourt à des herbicides ayant le même mode d'action ou applique une multitude d'herbicides peut néanmoins déboucher avec le temps sur une intense pression sélective qui favorisera les adventices plus résistantes, ce qui nécessitera éventuellement un usage plus intense d'herbicides pour lutter contre les biotypes RH. L'histoire a montré à maintes reprises que la variété des systèmes agricoles est la pierre angulaire ...

Lentil, Lens culinaris subsp. culinaris Medic., is an important legume crop on the Canadian prairies. Anthracnose, a fungal disease caused by Colletotrichum truncatum (Schwein.) Andrus & W.D. Moore, is a major barrier to seed yield and quality in lentil. Pathogenicity testing has revealed two races, Ct1 and Ct0, of C. truncatum in western Canada. No cultivar or landrace of cultivated lentil has been reported with resistance to anthracnose race Ct0. A search for Ct0 resistance in the wild species identified a high frequency of resistant accessions in Lens ervoides (Brign.) Grande. To incorporate higher levels of resistance from L. ervoides to the two races of anthracnose, a cross was made between a susceptible L. culinaris cultivar, Eston, and a resistant accession of L. ervoides germplasm, L‐01‐827A, which has both Ct0 and Ct1 resistance. Embryo rescue technique was used to obtain an F1 hybrid. Single‐seed descent was used to advance the individual F2 plants to F7:8 recombinant inbred lines. Evidence of transfer of resistance to both anthracnose races Ct1 and Ct0 from the wild species to cultivated lentil is presented. Chi‐square tests of goodness of fit indicated that resistance to race Ct1 and race Ct0 may be conferred by two recessive genes. However, these results may be skewed due to variable fertility encountered in development of the population. Selection of resistant lines for use in pyramiding genes in breeding programs should result in a more durable level of resistance to anthracnose in lentil.

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