A split‐root experiment shows that iron is required for nodule initiation in Lupinus angustifolius L.

Abstract

summaryA split‐root system was used to examine the effect of iron on nodule initiation and development in lupins (Lupinus angustifolius L. cy. Yandee) in solution culture. An inoculum of Bradyrhizobium was added to one half of the root system which then received either 0‐05 or 2‐5 μM iron, in various combinations. Where inoculum was present along with a low concentration of iron, the numbers of nodule initials and nodules were markedly decreased, irrespective of whether or not the shoots of the plant were adequately supplied with iron. The limitation to nodule formation was independent of host plant growth. Where half of the roots were given 2–5 μM iron, plants translocated little iron to the roots grown in the other compartment at 0.05 μm iron. Foliar application of iron obviated deficiency symptoms in the shoot but did not increase nodulation. We conclude that, for nodule initiation, iron is required either in the external solution or within the root.