The root morphology of Lupinus angustifolius in relation to other Lupinus species

Abstract

Commercial L. angustifolius cultivation is restricted to acid to neutral coarse-textured soils in Australia. An unsuitable root system may be part of the reason for the poor performance on fine-textured or alkaline soils. As a first step to examine this question plants of 12 annual Lupinus species were grown in a coarse soil with the aim of describing the range of root morphologies within the genus and to compare these to commercial L. angustifolius. A wide range of rooting patterns were observed. The differences in the dominance of the taproot was pronounced between species. The commercial genotype of L. angustifolius occupied an extreme within the range of root morphologies of the species. Roots of L. angustifolius consisted of a dominant taproot and a relatively high number of primary lateral roots but few secondary roots. In contrast, the primary, secondary and tertiary lateral roots of L. pilosus, L. mutabilis, L. atlanticus, L. palaestinus and L. micranthus were more dominant than the taproot. The length and distribution of primary lateral roots along the taproot also varied between species. The number of primary lateral roots fell rapidly with depth in L. angustifolius and L. mutabilis, while the other species had a more even distribution. L. angustifolius had a less extensive root system and relatively thick roots when compared to species such as L. albus and L. mutabilis. L. luteus also had relatively thick roots. The relatively thick roots and less extensive lateral root system in commercial L. angustifolius may partially explain its poor growth on fine-textured soils, where a greater proliferation of finer, lateral roots may be necessary. Proteoid root formation was observed for L. albus, L. cosentinii, L. pilosus, L. palaestinus, L. micranthus, L. digitatus, L. princei and L. atlanticus. They were particularly numerous in L. micranthus and L. albus. The structure of proteoid root clusters varied between species.