Nodulation and Nitrogenase Activity of Peanuts Inoculated with Single Strain Isolates of Rhizobium1

Abstract

Abstract Nodulation and nitrogenase activity (μM C2H4/plant/hr) for 48 diverse peanut (Arachis hypogaea L.2) genotypes were determined in a field site where the soil supported high populations of endemic rhizobia. These same rhizobia and peanut genotypes had previously been evaluated in a greenhouse study. Both host genotypes and rhizobial strains significantly influenced nodulation and nitrogenase activity. Roots of Virginia-type host plants were better nodulated and exhibited higher nitrogenase activity than genotypes of the fastigiate type. Florigiant, the predominant cultivar in the Virginia-North Carolina area, produced the most nodules and had the greatest nitrogenase activity. Variation in nodulation and nitrogenase activity for the single strain isolates in the presence of naturally occurring field populations indicated that the strains were able to compete for nodule sites. Strains both less and more effective than the naturally occurring rhizobial population were observed. Nitrogenase activity of the strains was correlated with previous greenhouse results suggesting that greenhouse evaluation of rhizobial strains for peanuts is useful as a preliminary screen before evaluation in the field.