Can low-dormancy oilseed rape (Brassica napus) genotypes be used to minimize volunteer problems?

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The potential of oilseed rape seeds from harvest losses to persist in the soil and to emerge later as volunteers in following crops is mainly driven by the ability of the seeds to go into dormancy under certain soil conditions. Using low-dormant oilseed rape cultivars could reduce volunteer problems considerably, but up to now there are unanswered questions as to whether (1) the trait is heritable and robust in different environments and whether (2) the variability in dormancy between and within cultivars allows for the selection of low-dormancy lines. Three field trials and one greenhouse trial were conducted from 2008 to 2010 at two locations in South West and Northern Germany to assess the effect of cultivar, location and year on dormancy characteristics of open-pollinated winter oilseed rape cultivars. A simple selection was performed in the field and in the greenhouse for low-dormant individual plants, and the offspring of these plants (potential volunteers) were tested for the stability of the trait under field conditions.Dormancy was mainly influenced by cultivar, and to a lesser extent by location, year and their interactions. There was also variation between cultivars depending on location and year between 1% and 90%, with a heritability of the trait ‘dormancy’ of h2=0.96. The dormancy values of the seeds from cultivars at both locations in both years were strongly correlated (R2=0.93). Individual plants within nearly every cultivar also varied significantly in their dormancy potential. The offspring of low-dormant individual plants, which had been selected from different cultivars, also produced seeds with a level of dormancy<5% under field conditions. In conclusion it seems feasible to use the trait ‘low dormancy’ in oilseed rape to successfully control volunteers in following crops in different environments. Variability of the dormancy trait between and within cultivars should enable breeders to select low-dormancy cultivars or individual plants to further develop low-dormant lines from nearly every open-pollinated cultivar.