Dynamics of dormancy during seed development of oilseed rape (Brassica napus L.)

Abstract

Seed dormancy is a critical factor in determining seed persistence in the soil and can create oilseed rape (Brassica napus L.) volunteer problems in subsequent years. A 3-year field trial in south-west Germany investigated the effects of seed maturity on primary dormancy and disposition to secondary dormancy of ten oilseed rape varieties (lines) in 2009 and 2010, and of five imidazolinone-tolerant varieties (hybrids) in 2014. Fresh seeds were sampled weekly from about 30 d after flowering (DAF) until full maturity and tested for dormancy on the day of seed collection. Primary dormancy decreased from a high level of 70−99% at 30−40 DAF to 0−15% after 7−14 d, coinciding with embryo growth and depending on variety and year. For some oilseed rape varieties, 30−50% primary dormancy was still present in mature seeds. Depending on variety, disposition to secondary dormancy was nearly zero at the early stage of seed development, increased to its highest level during development, and decreased afterwards. Some varieties maintained a high level of secondary dormancy at maturity or during the entire seed development period. The correlation between primary dormancy and secondary dormancy was significantly positive at early seed development (r = 0.95, 50 DAF), but declined in mature seeds. Environmental conditions during ripening are also expected to affect dormancy dynamics. The deeper insights into dormancy formation of oilseed rape provide the possibility to improve harvest time and harvest method, and to better assess the potential for volunteer oilseed rape in following crops.

A review of the relationship between primary and secondary dormancy, with reference to the volunteer crop weed oilseed rape (Brassica napus)

“…() stated that, ‘We now know that rape seeds have no primary dormancy, and consequently they have to be exposed to a combination of darkness (or far‐red light) and stress conditions to prevent immediate germination and to establish secondary dormancy’. Brassica napus seeds can enter dormancy during their development on the mother plant, but it is reduced to a minimum level by the time of seed maturity (Finkelstein et al ., ; Haile & Shirtliffe, ; Huang et al ., ). The intensity of dormancy in freshly matured seeds depends on genotype and environmental conditions during seed development (Finkelstein et al ., ; Haile & Shirtliffe, ; Huang et al ., ).…”

“…Huang et al . () reported that dormancy was present in 73–89% of the seeds of 10 varieties (lines) of B. napus 28 days after flowering (DAF) in 2009 and in 50–95% of the seeds 35 DAF in 2010. They indicated that the peak of dormancy occurred 42 DAF but decreased to 0–15% within the next 14 days on the mother plant.…”

Overcoming seed dormancy in oilseed rape (Brassica napus L.) with exogenous compounds

“…Primary dormancy can occur in pre‐mature seeds during seed development on the mother plant of OSR (Huang et al ., ). A reduction in primary seed dormancy would be beneficial for managing volunteer OSR, in case of natural pod shatter or pod damage caused by heavy rainfall or hailstorms before harvesting.…”

“…Strategies to reduce OSR seed persistence in the soil already exist. By growing OSR varieties that tend to have lower secondary dormancy levels, the likelihood of seed survival in the soil is reduced (Gruber et al ., ; Huang et al ., ). In areas with harsh winter conditions, the soil seedbank is decreased by winterkill because emerging OSR volunteers perish as a result of very low temperatures in winter (Geddes & Gulden, ).…”

“…Moreover, volunteers can reduce OSR oil quality and potentially spread herbicide‐resistant genes. Apart from secondary (induced) dormancy, OSR seeds can show primary (innate) dormancy to a small extent at harvesting (Momoh et al ., ; Huang et al ., ), which rapidly decreases to zero after <6 months of storage (Gruber et al ., ).…”