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

Abstract

The extent of intraspecific variability for N2 fixation among 100 southernpea (cowpea) genotypes was determined, and a screening technique was developed to measure the character. Significant differences in N2 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 N2 fixation efficiency in cowpea.

The Influence of Genotype on Diurnal and Seasonal Patterns of Nitrogen Fixation in Southernpea (Vigna unguiculata (L.) Walp)1

“…Diurnal study. Two southernpea cultivars, representing high ('H-Brown Crowder') and low ('L-Bush Purple Hull') N2 fixa tion potential (9), were hand planted and inoculated with a commercial mixed strain Rhizobium inoculant in the field, at College Station, Texas on May 8, 1978. The soil type was a Lufkin fine sandy loam and the experimental design was a randomized block with 5 replications.…”

“…Time course study. In conjunction with the diurnal study, a field time course experiment was carried out using 4 high N2 fixing genotypes ('H-Brown Crowder', 'H-Knuckle Purple Hull', 'H-Calico Crowder', 'H-TXCS 8') and 3 low N2 fixing genotypes ('L-Chinese Red', 'L-TX 460', L-Bush Purple Hull') (9). The experimental design was a randomized block with 5 replications.…”

“…However, few reports have been found regarding the role of plant genotype in these pat terns (1,3,4). The purpose of this investigation was to deter mine the influence of southernpea genotypes, with differential N2 fixing potential (9), on diurnal and seasonal patterns of N2 fixation.…”

Interaction Between Rhizobial Inoculation and Fertilizer Nitrogen in Five Cowpea Cultivars

“…High levels of fertilizer N were found to reduce root hair infection (5,16), nodule number (3), nodule growth (21), ni trogenase activity ( 10 ), and the total amount of biologically fixed N (1). The magnitude of inhibition was influenced by plant species (1), host genotype (10,25), growing season (18), strain of Rhizobium (18), and the forms of N fertilizer (4). Synergistic effects of ap plied N on N2 fixation with low levels of N were also reported in soybean (Glycine max) and cowpea (7).…”

“…The three high (H) and two low (L) N2-fixing, indeterminate cow pea cultivars used were 'H-Califomia Blackeye N o. 5 ' , 'H -B row n C ro w d er' , 'H-Tennessee White Crowder', 'L-Lady', and 'L-Mississippi Silver' (25). Four split plots were allocated with four fertilizer N levels, 0, 14, 28, and 84 kg-ha-1.…”