Application of 1-aminoocyclopropane-1-carboxylic acid, an ethylene precurso
r, decreased nodulation of Macroptilium atropurpureum by Bradyrhizobium elk
anii. B. elkanii produces rhizobitoxine, an ethylene synthesis inhibitor. E
limination of rhizobitoxine production in B. elkanii increased ethylene evo
lution and decreased nodulation and competitiveness on M. atropurpureum, Th
ese results suggest that rhizobitoxine enhances nodulation and competitiven
ess of B. elkanii on M. atropurpureum.