Breeding system and pollination biology of Belgian oilseed rape cultivars (Brassica napus)

Oilseed rape (Brassica napus L. ssp napus) is considered to be an insect-pollinated species, but the degree of insect-dependent pollination differs among cultivars and the contribution of wind pollination remains a matter of debate. In addition, the breeding system has not been assessed for several new cultivars and spontaneous self-pollination has rarely been addressed. This study aimed to clarify the current situation in Belgium by analyzing the breeding system and pollination biology of the most cropped Belgian cultivars. We performed hand pollination under controlled conditions to analyze the breeding system and conducted field observations to identify the main pollen vectors. The results show that the studied cultivars were highly self-compatible (self-compatibility index = 1). Nevertheless, pollen vectors were necessary to produce high fruit and seed set because spontaneous self-pollination occurred at a low rate under greenhouse conditions. All cultivars produced abundant nectar (1.2 L per flower per 24 h) with a high sugar content (48%). Surprisingly, very few insects were observed: only 1.1% of the flowers received insect visits during their lifespan. Moreover, wind pollination was only responsible for a small portion (2.5%) of the pollen deposition on stigmas. Despite the lack of pollen vectors, approximately 300 pollen grains were present per stigma. The indirect effects of insects and wind, which favor contact within and between flowers, ensure high fruit and seed set in the main Belgian oilseed rape cultivars