In recent years (1977 and 1979-81) the collecting missions made to Central and South America by Dr. R. Reid of CSIRO have been of particular importance. His 18-month visit to Mexico and Colombia resulted in more than 2000 accessions of the genera Centrosema, Desmanthus, Leucaena, Macroptilium and Stylosanthes.

As a result of such collections, and the immense amount of subsequent investigation and evaluation undertaken by State Departments and CSIRO, some 70 new tropical cultivars were released through State Herbage Plant Liaison Committees between 1961 and 1984. Of these only eight were varieties bred in Australia and the remainder were selections from introduced species. Computerised catalogues of collected species have been prepared according to taxonomic and environmental criteria, and these are now available for use nationally and internationally.

Australia's leading position in research on the genetic resources of tropical forages is internationally recognised .[76] CSIRO and QDPI staff now provide a vigorous service in the supply of seed, rhizobia and information to overseas tropical countries which has developed into an important element in the total activity of forage germplasm exchange.

Introduction of rhizobial bacteria

The special value of leguminous plants in Australian agriculture, where soils are often low in nitrogen, is due to their close association with specialised symbiotic bacteria (Rhizobia) which occur in their root nodules and which enable the host plant to use atmospheric nitrogen which is not otherwise available to higher plants. For this symbiotic relationship between legume and rhizobia to function effectively, however, appropriate types of bacteria must be present in the soil in which the plant roots are growing and soil conditions (e.g. soil pH, temperature and moisture content) must be conducive to nodule formation and function.

Although Australia has many native legumes, such as species of Acacia, which are generally well nodulated by indigenous rhizobia, almost all the legumes utilized in agriculture, whether for grazing, forage or grain, have been introduced and therefore they have required the associated introduction of specific rhizobia. A great deal of casual introduction of such bacteria occurred early in settlement and resulted in the concomitant spread of both the introduced legumes and their specific rhizobia wherever conditions of soil and climate were favourable to both partners. In many circumstances, however, it has been necessary to introduce the required root-nodule bacteria deliberately with the sown seed. This has proved necessary, for example, when a more effective symbiosis is required than can be secured with locally established rhizobial strains, when new varieties of leguminous host make new demands for specific strains, or when conditions prior to soil amelioration and seed-sowing have been unfavourable for rhizobial survival and multiplication.

Australian Academy of Technological Sciences and Engineering