Breeding methodologies for cultivated lucerne
(Medicago sativa L.), an autotetraploid, have changed
little over the last 50 years, with reliance on polycross methods and
recurrent phenotypic selection. There has been, however, an increase in our
understanding of lucerne biology, in particular the genetic relationships
between members of the M. sativa complex, as deduced by
DNA analysis. Also, the differences in breeding behaviour and vigour of
diploids versus autotetraploids, and the underlying genetic causes, are
discussed in relation to lucerne
improvement.Medicago falcata, a member of the
M. sativa complex, has contributed substantially to
lucerne improvement in North America, and its diverse genetics would appear to
have been under-utilised in Australian programs over the last two decades,
despite the reduced need for tolerance to freezing injury in Australian
environments.
Breeding of lucerne in Australia only commenced on a large scale in 1977,
driven by an urgent need to introgress aphid resistance into adapted
backgrounds. The release in the early 1980s of lucernes with multiple pest and
disease resistance (aphids, Phytophthora,
Colletotrichum) had a significant effect on increasing
lucerne productivity and persistence in eastern Australia, with yield
increases under high disease pressure of up to 300% being recorded over
the predominant Australian cultivar, up to 1977, Hunter River. Since that
period, irrigated lucerne yields have plateaued, highlighting the need to
identify breeding objectives, technologies, and the germplasm that will create
new opportunities for increasing performance. This review discusses major
goals for lucerne improvement programs in Australia, and provides indications
of the germplasm sources and technologies that are likely to deliver the
desired outcomes.