EVALUATION OF THE RHIZOBIUM POPULATION OF PIGEONPEA AND COWPEA RHIZOSPHERE AFTER INOCULATION WITH SEVERAL RHIZOBIUM STRAINS

Abstract

Pigeonpea [Cajanus cajan (L.) Millsp.] and cowpea [Vigna unguiculata (L.) Walp.] seeds were inoculated with broth cultures of Rhizobium strains 3278, 3458, and 3472 at a population of ≈9.5 × 10 g viable cells/ml. They were planted at three air temperature regimes: 20/10C, 30/20C, and 38/25C (day/night), which generated variable rhizosphere temperatures of 17/6C, 26/15C, and 33/20C, respectively. Seeds and/or seedling roots were sampled at 3, 7, 11, and 15 days after planting and Rhizobium survival was enumerated as viable cells on agar media. Only strain 3458 in association with pigeonpea genotype ICPL8304 had a higher population at day 15 than that at the earlier sample dates. The duration of the strains in the rhizosphere, rather than temperature, influenced population changes. No strain showed a consistent increase in cell numbers from inoculation to 15 days after planting. There was no clear pattern of population changes for any strain within or across temperatures, hence it was difficult to identify any strain as having superior growth habits over another.