Nodule Distribution among Root Morphological Components of Field-grown Cowpeas

Abstract

Field experiments were conducted in 1985 at Fort Pierce, Fla., and Bixby, Okla., to quantify and describe the distribution of nodules among root morphological components of cowpea [Vigna unguiculata (L.) Walp.]. Plants of `Knuckle Purplehull', `Mississippi Cream', and `White Acre' were sampled by cultivar on separate dates at three growth stages: pre-anthesis, seed initiation, and harvest, when most pods were dry. Root masses were partitioned into adventitious, basal, lateral, and taproot components. Nodules were removed from roots, grouped according to root morphological component of origin, and weighed. No linear correlation was found between the weight of a particular root morphological component and the nodule weight associated with that component. Total root weight and total nodule weight also were not strongly correlated. Nodule weights usually were lower at harvest than at earlier stages of ontogeny, especially for nodules from taproots. Although ≈70% of the root mass was in the taproot and its associated laterals at both locations, the taproot per se was not the primary locus of nodulation. Instead, most nodules generally were located on the basal and lateral roots. When percentage distribution of total nodule weight was examined, neither growth stage nor cultivar was found to affect nodulation of basal or lateral roots.