Secondary Dormancy of a Diverse Collection of Annual Brassica napus L. Genotypes and the Relationship with Seed Germination, Vigour and Quality Traits

Abstract

Volunteer canola (Brassica napus L.), defined as canola germinating and emerging after the intended cropping season, is the fourth most occurring weed on the Canadian prairies. The largest contribution of seed into the soil seed bank occurs from pod shatter during maturity and harvest. Gene transfer via pollen flow between different varieties is the major concern with volunteer canola. Gene transfer may result in the stacking of herbicide tolerance types in subsequent volunteer canola populations. Seed dormancy is the physiological mechanism prolonging the presence of viable seed in the soil seed bank. Specifically, canola has a high propensity to be induced into secondary dormancy (SD) under adverse environmental conditions not conducive for germination. Previously screened Canadian commercial material ranged from 0-90% propensity to enter SD. A reduction of SD in modern canola varieties may result in lower seed bank persistence, however, the indirect effect this would have on other seed traits is not known. This study examined a diverse collection of annual B. napus genotypes produced in contrasting maternal environments for SD as well as seed germination, vigour and quality traits. Absolute SD values ranged from 0-77% dormant in the diversity collection screened. Genotype was shown to be the main contributor to the variability in SD observed (50%), the interactions between the genotype and environment had a moderate contribution (30%) and very little contribution from maternal environment alone was observed. Genotypes with low SD were more consistent across maternal environments compared to mid and high SD genotypes. No association was observed between SD and germination time or seed vigour traits in the genotypes examined. A significant positive correlation between SD and total protein content was found (r= 0.34; P < 0.001). Total oil content was negatively correlated to SD (r= -0.24; P < 0.05), likely due to the inverse relationship between oil and protein. From the results in this study, the reduction of SD as a breeding objective in canola breeding programs is feasible as the trait is largely genetically controlled. Likewise, the reduction of SD is unlikely to impact seed germination or vigour traits and SD should not be a large contributor to poor stand establishment of canola.