ABSTRACT
Summary Annual medics (Medicago spp.) are the basic legume for nitrogen fixation in the alkaline soils of southern Australia. Not all individual species are well adapted to all soil types, one difficult soil being the highly alkaline clay loam where annual rainfall is less than 500 mm. The first gama medic (M. rugosa) cultivar, Paragosa, was well adapted to the clay-loam soil type but proved to be susceptible to germination after summer thunderstorms, and seedlings died in the following drought. Many gama medic accessions were then grown in an attempt to select a genotype capable of maintaining seedcoat impermeability during the summer but having enough permeable seed by mid-April to allow dense regeneration. Other essential criteria included good winter herbage production, earliness of flowering, and high seed yield. These accessions were grown to maturity in the field nursery and sampled at regular intervals over the summer and autumn to measure changes in seedcoat permeability. Subsequent sward sowings in different environments allowed measurement of the other criteria. Screening of 1,364 genotypes of 13 species revealed the variability of gama medic compared with other species. Although gama medic from the eastern Mediterranean region maintained a high level of seedcoat impermeability, accession types from Greece, Italy, and Portugal displayed a range of changes between maturity and mid-April. Evaluation of this and other criteria resulted in the development of the cultivar Paraponto. Species other than those previously recognized may have application to specific environments. A more intensive search for, and evaluation of, genotypes of relatively rare species, such as gama medic, as well as other potentially useful species could result in more productive and better adapted cultivars in the future.
