However, N2 needs to be converted first into a biologically useable form through the unique process of N2 fixation [1]. The incorporation of fixed N into biologically essential macromolecules provides the basis for the continuance of life on Earth. Bioavailable N can be chemically synthesized (primarily through the products obtained from the Haber-Bosch more information process) or biologically fixed by N2-fixing diazotrophs. The highest contribution to biological fixation occurs from the process of symbiotic nitrogen fixation (SNF). The estimated total annual input from SNF ranges from 139 – 175 million tons [2] which provides ~70% of the N currently utilized in agriculture. However, various constraints from edaphic conditions can limit SNF capacity in certain agricultural areas.

To extend productive crops and pastures into these regions, considerable efforts have been devoted to sourcing legume hosts and their compatible microsymbionts from different geographical locations that are edaphically and climatically suited to the challenging areas into which they are to be introduced [3]. These selection programs have enabled the domestication of new Mediterranean legume species that have overcome the deficiencies of the use of traditional species [4]. Seven species new to Australian agriculture have been commercialized since 1993 including the Papilionoid legume Ornithopus sativus (serradella) [4]. This hard-seeded deep-rooted and acid tolerant pasture legume has shown particular promise in acidic sandy soils exposed to low rainfall [4], with the potential to be established in four million hectares of sandy soils for which no other suitable legume pasture exists [5].

The hard seeded nature of this legume makes it well adapted to crop rotation systems [4]. Currently, serradella is the most widely sown pasture in Western Australia and has proven to be a highly productive legume with high nutritive value [4]. The strains of lupin-nodulating Bradyrhizobium that also nodulate seradella are unusual since they have the capacity to establish symbioses with Mediterranean derived herbaceous and crop legumes endemic to the cool climatic regions of the world. Before the 1990s, the commercial inoculant for serradella (Ornithopus spp.) in Australia was Bradyrhizobium sp. strain WU425, however during the breeding and evaluation of well adapted cultivars of O.

sativus, it was revealed that WSM471 produced 15% more biomass with this legume than did WU425 [5]. Strain WSM471 was isolated from nodules of O. pinnatus collected in Western Australia, in 1982, although it was almost Dacomitinib certainly accidentally introduced to Australia [6]. Because of its superior capacity to fix nitrogen with O. sativus relative to other strains of Bradyrhizobium, strain WSM471 was released as a commercial inoculant for this legume in Australia in 1996 [7] and remains in current usage. This strain is also the commercial ��back-up�� for inoculation of lupins in Australia.