STEM NODULATION IN LEGUMES - DIVERSITY, MECHANISMS, AND UNUSUAL CHARACTERISTICS

Rhizobia can establish a nitrogen-fixing symbiosis with plants of the Leguminosae family. They elicit on their host plant the formation of n ew organs, called nodules, which develop on the roots. A few aquatic l egumes, however, can form nodules on their stem at dormant root primor dia. The stem-nodulating legumes described so far are all members of t he genera Aeschynomene, Sesbania, Neptunia, and Discolobium. Their rhi zobial symbionts belong to four genera already described: Rhizobium, B radyrhizobium, Sinorhizobium, and Azorhizobium. This review summarizes our current knowledge on most aspects of stem nodulation in legumes, the infection process and nodule development, the characterization and unusual features of the associated bacteria, and the molecular geneti cs of nodulation. Potential use as green manure in lowland rice of the se stem-nodulating legumes, giving them agronomical importance, is als o discussed.