SelectingRhizobium phaseoli strains for use with beans (Phaseolus vulgaris L.) in Kenya: Tolerance of high temperature and antibiotic resistance

Abstract

Forty one strains of Rhizobium phaseoli were screened for the ability to multiply at high temperatures on yeast extract-mannitol agar. Most strains were tolerant of 30°C, eight strains were tolerant of 45°C and two of 47°C although the rate of multiplication was reduced at 45–47°C. The high temperature-tolerant strains were isolated from Kenyan soils and were fast-growing. Seven of the eight strains tolerant of 45–47°C lost their infectiveness after incubation at high temperature but four strains tolerant of 40°C remained infective after incubation at that temperature. Thirty six strains were resistant to 200 μg ml−1 streptomycin sulphate and 29 strains to 200 μg ml−1 spectinomycin dihydrochloride. Eight strains were resistant to both antibiotics each at 200 μg ml−1. Two of the double-labelled antibiotic-resistant mutants lost their infectiveness onPhaseolus vulgaris. The response to acidity was unaltered and two of the mutants showed a decrease in temperature tolerance. The doublelabelled mutants were recoverable from two Kenyan soils.