THE ROOT MORPHOLOGY OF LUPINUS-ANGUSTIFOLIUS IN RELATION TO OTHER LUPINUS SPECIES

Commercial L. angustifolius cultivation is restricted to acid to neutr al coarse-textured soils in Australia. An unsuitable root system may b e part of the reason for the poor performance on fine-textured or alka line soils. As a first step to examine this question plants of 12 annu al Lupinus species were grown in a coarse soil with the aim of describ ing the range of root morphologies within the genus and to compare the se to commercial L. angustifolius. A wide range of rooting patterns we re observed. The differences in the dominance of the taproot was prono unced between species. The commercial genotype of L. angustifolius occ upied an extreme within the range of root morphologies of the species. Roots of L. angustifolius consisted of a dominant taproot and a relat ively high number of primary lateral roots but few secondary roots. In contrast, the primary, secondary and tertiary lateral roots of L. pil osus, L. mutabilis, L. atlanticus, L. palaestinus and L. micranthus we re more dominant than the taproot. The length and distribution of prim ary lateral roots along the taproot also varied between species. The n umber of primary lateral roots fell rapidly with depth in L. angustifo lius and L. mutabilis, while the other species had a more even distrib ution. L. angustifolius had a less extensive root system and relativel y thick roots when compared to species such as L. albus and L. mutabil is. L. luteus also had relatively thick roots. The relatively thick ro ots and less extensive lateral root system in commercial L. angustifol ius may partially explain its poor growth on fine-textured soils, wher e a greater proliferation of finer, lateral roots may be necessary. Pr oteoid root formation was observed for L. albus, L. cosentinii, L. pil osus, L. palaestinus, L. micranthus, L. digitatus, L. princei and L. a tlanticus. They were particularly numerous in L. micranthus and L. alb us. The structure of proteoid root clusters varied between species.