The role of boron nutrition in seed vigour of oilseed rape (Brassica napus L.)

Seed vigour is of great importance for seedling establishment and plant productivity. Despite the high boron (B) demand of oilseed rape and the potential benefit of B for improved seed vigour, it is still unclear whether B fertilization to mother plants is effective to enrich B in seeds to an extent that improves seed vigour. We addressed this question and investigated first the dynamics of B enrichment in mother plants and their seeds and then the influence of B on seed vigour using seeds that either were B-enriched from their mother plants or received B from soil fertilization. Oilseed rape was grown in a pot experiment and supplied with different B levels. Developing and mature seeds were analysed for biomass and mineral element profiles. In mature seeds, embryos and seed coats were analyzed separately. Seeds were subsequently germinated under no, low, sufficient or excessive B supplies to assess germination rates and seedling establishment. During seedling establishment external B supply strongly promoted water and nutrient uptake as well as biomass formation. When maternal plants were supplied with elevated levels of B, seeds became enriched with B mainly in the seed coat. Sowing these seeds in low B substrate did not provide any advantage for germination or seedling establishment. By contrast, nutrient uptake and especially tissue water content strongly increased with external B supply but irrespective of seed B levels, except when excess B was supplied. Additional B supply to mother plants allows for an increase in seed B levels. However, additional B is mainly the seed coat and ineffective in improving seed germination or seedling establishment. In contrast, B fertilization to the soil effectively improves seedling establishment. We conclude that adequate B supply via the soil is more effective to improve seed vigour than fertilization of mother plants for B enrichment in seeds.