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

Abstract

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 cropBrassica napus, ten feralB. napusaccessions originating from seeds collected in the field and nine accessions of the closely related ruderal speciesBrassica rapa. When buried for a year in the field, seeds of the wildB. rapadisplayed, as expected, much higher survival fractions than those of domesticatedB. napusat two different locations in The Netherlands. Compared toB. napus, B. rapaproduces 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. rapaseeds had lower and more variable germination fractions than those ofB. napus; a small fraction (4.6%) of theB. rapaseeds showed primary dormancy. Rather surprisingly,B. napusdisplayed genetic differences in germination at low temperature, and germination fractions at 5°C 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 modifiedB. napus.