Comparison of the crop speciesBrassica napusand wildB. rapa: characteristics relevant for building up a persistent seed bank in the soil

Abstract

2013). Comparison of the crop species Brassica napus and wild B. rapa: characteristics relevant for building up a persistent seed bank in the soil. AbstractCan seed characters be used for predicting the presence of a persistent seed bank in the field? We address this question using ten cultivars of the crop Brassica napus, ten feral B. napus accessions originating from seeds collected in the field and nine accessions of the closely related ruderal species Brassica rapa. When buried for a year in the field, seeds of the wild B. rapa displayed, as expected, much higher survival fractions than those of domesticated B. napus at two different locations in The Netherlands. Compared to B. napus, B. rapa produces relatively small seeds with high levels of aliphatic glucosinolates and a thick seed coat. However, within each species none of these characters correlated with seed survival in the soil. At low temperatures, B. rapa seeds had lower and more variable germination fractions than those of B. napus; a small fraction (4.6%) of the B. rapa seeds showed primary dormancy. Rather surprisingly, B. napus displayed genetic differences in germination at low temperature, and germination fractions at 58C correlated negatively with seed survival in the soil. Our comparisons between and within the two species suggest that foregoing germination at low temperatures is an important character for developing a persistent seed bank. We discuss our results in light of environmental risk assessment of genetically modified B. napus.

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

“…In some studies, authors used more than one incubation temperature (e.g. De Jong et al ., ; Soltani et al ., ), but we report only the temperature for determining primary dormancy.…”

“…For example, in a study by De Jong et al . (), so‐called fresh seeds of B. napus germinated to 100% at all test temperatures (15–25°C) in light, which might suggest that the seeds were ND at maturity. However, their fresh seeds were collected at maturity in July and then stored at room temperature for 3 months before they were tested for germination.…”

Landscape-level persistence and distribution of alien feral crops linked to seed transport

“…Seeds of B. rapa, the most common Brassica species in our study system, are thought not to have primary dormancy (Adler et al, 1993;de Jong et al, 2013). Seeds of B. napus on the other hand, can have limited primary dormancy (Baskin and Baskin, 2001) such that cold stratification can increase germination rates by around five percent (de Jong et al, 2013), although this increased germination rate can be negated by increased mortality of nondormant seeds (Adler et al, 1993).…”

“…Seeds of B. napus on the other hand, can have limited primary dormancy (Baskin and Baskin, 2001) such that cold stratification can increase germination rates by around five percent (de Jong et al, 2013), although this increased germination rate can be negated by increased mortality of nondormant seeds (Adler et al, 1993). Nevertheless, the possibility remains that our decision not to cold stratify seeds resulted in slight underestimates of seed bank densities for B. napus populations.…”

“…Every two weeks any germinated seedlings were pricked out and the number of Brassica seedlings recorded, until no further germination occurred. Following current practice for Brassica, no freezing or stratification treatment was administered to the soil samples (de Jong et al, 2013;Gruber et al, 2014).…”