Growth and Distribution of Boron in Oilseed Rape (Brassica napus L.) as Affected by Boron Supply

Oilseed rape (Brassica napus L.) is one of the most important oilseed crops. It has relatively high boron (B) requirements for growth. In this study, a hydroponic experiment was performed to determine the critical B requirement and B distribution in B. napus. The plants were grown for four weeks at a range of B levels (from 0.25 to 1000 µM) supplied in a nutrient solution. The results showed significant differences in the root and shoot dry matter and B accumulation in these tissues among the supplied B levels. Severe visible symptoms of B deficiency were observed on the leaves at levels lower than 1 µM B and toxicity at 1000 µM B in the nutrient solution. The maximum shoot and root dry matter were recorded at 25 µM B in the nutrient solution. The plants supplied with the lowest and the highest B levels produced 35% and 37% less shoot dry matter than those supplied with 25 µM B, while the corresponding decreases in the root dry matter were 48% and 36%, respectively. The critical concentration of B, which is the lowest concentration at which plants produce 90% of the maximum shoot dry matter, was proven to be 1 µM B for oilseed rape. At this level of external B supply, the B concentration in the shoot was 26.9 mg kg(−1) DM. It was found that with the increase in B levels in the nutrient solution, the relative distribution of B between the roots and the shoots shifted in favor of the shoots.