Boron nutrition and mobility,and its relation to the elemental composition of greenhouse grown root crops I. Rutabaga

Abstract

The nutrition and mobility of B, and its relation to the elemental composition of two cultivars of rutabaga (Brassica napus ssp. rapifera cv. Laurentian and Wilhelmsberger) plants were investigated in greenhouse experiments. Laurentian exhibited a greater response than Wilhelmsberger to continuing B deficiency as indicated by the severity in the roots of brown heart, of external roughness and elongation and of the decrease in B concentration. Signs of B deficiency were not found when the B contents of the root and young leaves were 27 and 56 ug g‐1 DM respectively. Root B levels of 14 and 17–20 μg g^‐1 gave moderate and slight internal signs of brown discoloration. Foliar applications of B partially restored the B concentrations of the roots; however, the mechanism of movement was unclear. The Mg, Mn and Zn contents of roots were the only elements that consistently increased and accumulated under B deficiency. The relative element composition of the root compared to the mature leaves is consistent with the root being supplied predominantly with nutrients by the phloem. Nutrient retranslocation was assessed from the ratio of element concentration in the roots or young leaves to that in the mature leaves. Although Mg, Mn and B exhibited limited mobility under adequate B nutrition they were translocated from mature leaves to younger tissues under B starvation. It is concluded that Wilheimsberger is by virtue of its greater capacity for the retranslocation of B to roots, less sensitive to B deficiency and the brown heart disorder.