A review of the genetic, physiological, and agronomic factors influencing secondary dormancy levels and seed vigour in Brassica napus L.

Dormancy in canola (Brassica napus L.) is a complicated process due to many overlapping and interacting factors affecting the absolute dormancy levels. It is unknown if seed dormancy plays a role in the poor stand establishment of planted canola but given that germination and dormancy are two ends of the same continuum, it has been suggested that dormancy may be a culprit of poor establishment. This review synthesizes literature pertaining to secondary dormancy in B. napus and the interaction of genetic, physiological, environmental, and agronomic factors. Seed germination and vigour and the interaction with dormancy are also addressed. The persistence of volunteer canola seed in the soil seedbank is a result of the induction of canola seed into secondary dormancy under adverse environmental conditions such as low temperature or low light. Genetics is a major influencing factor on absolute secondary dormancy (similar to 50%) in canola. Plant hormones abscisic acid and gibberellic acid and their interactions also influence dormancy with highly dormant genotypes having increased abscisic acid concentration in the seed. Seed sugars, seed storage proteins, glucosinolate content, and growth habit are all additional factors affecting absolute dormancy in B. napus. Furthermore, maternal environmental conditions affect dormancy levels. In addition to genetic, physiological, and environmental factors, farming practices such as harvest timing, and tillage regimes can influence secondary dormancy of canola seed that has entered the seedbank unintentionally. Given the documented high heritability of secondary dormancy, it is feasible to reduce secondary dormancy in canola cultivars; however, consideration of all interacting factors must be given.