Intraspecific Variability for Nitrogen Fixation in Southernpea (Vigna unguiculata (L.) Walp)1

Abstract

The extent of intraspecific variability for N 2 fixation among 100 southernpea (cowpea) genotypes was determined, and a screening technique was developed to measure the character. Significant differences in N 2 fixation efficiency were found among host plant genotypes following application of a standard commercial mixed strain Rhizobium inoculant. These differences were obtained whether the criterion used was nodule mass, nodule number of nitrogenase activity, as measured by the acetylene reduction assay. This variability is evidence of genetic control of the trait and suggests the possibility of breeding for increased N 2 fixation efficiency in cowpea.