Semienclosed Tube Cultures of Bean Plants ( Phaseolus vulgaris L.) for Enumeration of Rhizobium phaseoli by the Most-Probable-Number Technique

Abstract

The semienclosed tube culture technique of Gibson was modified to permit growth of common bean ( Phaseolus vulgaris L.) roots in humid air, enabling enumeration of the homologous (nodule forming) symbiont, Rhizobium phaseoli , by the most-probable-number plant infection method. A bean genotype with improved nodulation characteristics was used as the plant host. This method of enumeration was accurate when tubes were scored 3 weeks after inoculation with several R. phaseoli strains diluted from aqueous suspensions, peat-based inoculants, or soil. A comparison of population sizes obtained by most-probable-number tube cultures and plate counts indicated that 1 to 3 viable cells of R. phaseoli were a sufficient inoculant to induce nodule formation.