Adam Kondorosi - Böcker

The refinement of molecular techniques and the development of new probes of the phylogeny of diazotrophs has revealed an extreme biodiversity among the nitrogen fixers, which helps explain the role that nitrogen fixation plays in maintaining life on Earth. The most efficient ecosystems are those in which the bacteria are associated with a plant in differentiated organs to benefit crop productivity. Most short-term benefit from fundamental research on nitrogen fixation is likely to result in the improvement of existing nitrogen-fixing symbiotic or associative systems. Longer-term efforts are aimed at extending the nitrogen-fixing capacity to other organisms, including transfer of the genetic information for efficient nitrogen fixation into the plant genome and using current knowledge of microbe-plant interactions to extend symbiosis to cereals and, in particular, to rice. Related challenges in sustainable agriculture and forestry include the creation of new nitrogen-fixing associations. All of these topics were discussed at the 11th International Congress on Nitrogen Fixation, held in Paris in July 1997, the proceedings of which are presented in this book.

This work gives a comprehensive overview of our present molecular biological knowledge about the Rhizobiaceae, which can be called the best studied family of soil bacteria in the late 20th century. For many centuries they have attracted the attention of scientists because of their capacity to associate with plants and as a consequence also to specifically modify plant development. Some of these associations are beneficial for the plant, as is the case for the Rhizobiaceae subgroups collectively called rhizobia, which are able to fix nitrogen in a symbiosis with the plant hosts. This symbiosis results in the formation of root or stem nodules, as illustrated on the front cover. In contrast, several Rhizobiaceae subgroups can negatively affect plant development and evoke plant diseases. Examples are Agrobacterium tumefaciens and A. rhizogenes which induce the formation of crown galls or hairy roots on the stems of their host plants, respectively.