Lucerne biology and genetic improvement - an analysis of past activities and future goals in Australia

Abstract

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.

Breeding lucerne for persistence

“…In Australia, similar eras were recorded, but described as (i) the time up until the mid 1970s that was predominated by introductions but especially by the proliferation and use of the cultivar Hunter River; (ii) the time since the 1970s dominated by development and use of multiple pest-resistant cultivars; and (iii) the recent time that is placing an emphasis on new breeding objectives, use of technologies, and introduction of new germplasm (Irwin et al 2001).…”

“…falactas in North America. Local varieties and land races served as base populations for cultivar improvement in all geographies (Bouton 2001;Irwin et al 2001). The approach capitalised on natural selection for adaptation and demonstrates the important role adaptation plays in the success of lucerne cultivars.…”

“…In the past, lucerne was a key forage species in Australia because of its wide adaption range Clements 1989;Gramshaw et al 1989;Irwin et al 2001). Due to its commercial value and high management requirements, coupled with the restriction of seed importation, lucerne also experienced a sustained breeding effort in Australia Clements 1989;Irwin et al 2001).…”

“…Due to its commercial value and high management requirements, coupled with the restriction of seed importation, lucerne also experienced a sustained breeding effort in Australia Clements 1989;Irwin et al 2001). Recently, when 91 perennial legumes and herbs representing 47 species in 21 genera were evaluated over 3 years for herbage production, persistence and the potential to reduce ground water recharge at sites in New South Wales, South Australia and Western Australia, lucerne was reported to be the best performing species across all sites (Li et al 2008).…”

“…sativa, is the most important and widely grown forage legume in the world with~32 million hectares estimated to be cultivated mainly in the temperate regions of both the northern and southern hemispheres (Bouton 2001;Irwin et al 2001). Cultivated lucerne is an autotetraploid with 2n = 4x = 32 (Stanford 1951).…”