Development of Root Nodules in a Woody Legume, Prosopis glandulosa Torr.

The morphological and developmental patterns of nodules of Prosopis glandulosa Torr. var. torreyana vary, depending on the rhizobial inoculant. Inoculation with an effective nitrogen-fixing strain (WR1001) results in the development of an elongate, indeterminate nodule with conspicuous meristematic, cortical, and infected cell areas. Inoculation with an ineffective strain (L5) results in formation of small, irregularly shaped nodules having few meristematic cells and unevenly stained infected cells containing "clumps" of bacteria. Inoculation with a cowpea rhizobial strain (176A32) produces both elongate and spherical nodules, but the meristematic region is rarely discernible, and both senescing and viable cells are distributed throughout the infected area. These observations are particularly interesting in view of the widely held assumption that nodule shape is determined by the plant.