Quantitative and time-course evaluation of nodulation competitiveness of rhizobitoxine-producing Bradyrhizobium elkanii

Regression analysis of results from a mathematical competition model showed that rhizobitoxine production by Bradyrhizobium elkanii USDA94 gave this strain a nodulation competitiveness about 10 times greater than that of a non-rhizobitoxine-producing mutant strain on Macroptilium atropurpureum (Siratro). Rhizobitoxine enhancement of competitive nodulation occurred at a late stage in the time-course of nodulation. All other known rhizobial factors that affect nodulation competitiveness act in the rhizosphere and during the initial interaction with legumes. This unique late action of rhizobitoxine could prove advantageous in inoculant production, because inoculum often fails to nodulate in the latter stages of nodulation kinetics. (C) 2003 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.