Volunteer canola (B. napus) in western Canada
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In western Canada, survey and small plot research has shown that volunteer canola persists for at least four years in rotation (Derksen at al. 1999; Thomas et al. 1999). It is not clear whether this is due to persistence of the seedbank additions during harvest or the result of replenishment of the seedbank by subsequent volunteers. We are examining the life cycle of volunteer canola beginning with the seedbank additions incurred during harvest and as well as a focus on the seedbank ecology of this species in western Canada. Research in Europe has shown that B. napus can be readily induced into secondary dormancy by a combination of darkness and moisture stress (Pekrun, 1994). Nonetheless, field studies have revealed that only a small proportion of seeds persist via secondary dormancy in Europe (Pekrun et al. 1998). Canadian B. napus genotypes differ in their potential for induction into secondary dormancy using a laboratory assay. While some genotypes consistently exhibit low potential for the induction into secondary dormancy, others consistently exhibit high potential for the induction into secondary dormancy. High temperatures are perhaps the most important contributing factor to the induction of secondary dormancy, while low temperatures rapidly remove secondary dormancy. These observations suggest the seed ecology of a typical summer-annual weed. Furthermore, observations in a field experiment in 2000 revealed that volunteer canola germination was limited to the early portion of the growing season. Spring seedbank evaluations indicated far greater seed viability than was reflected by field emergence. It is was not clear if the seeds that did not emerge lost viability or were induced into secondary dormancy as our lab results would suggest. A more detailed field experiment examining the persistence of B. napus and induction into secondary dormancy was initiated.
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