Evaluation of a lucerne germplasm collection in relation to traits conferring grazing tolerance

Abstract

A collection of 90 accessions of different germplasm groups from the Medicago sativa complex was evaluated at Lodi, Italy, for dry-matter yield, time to anthesis, height of regrowth, plant diameter, stem density, vegetative recovery after winter, and presence of deep-set crown and ability to spread with creeping roots or rhizomes, these latter characters possibly contributing to grazing tolerance . The germplasm groups proved rather distinct for these traits, but all included types potentially suitable for grazing . Interesting types combining deep-set crown and high yield occurred mainly in subsp . x varia and materials originated from artificial crosses involving at various extent the subspecies falcata, sativa and x varia . Though belonging to subsp . sativa, "mielga" wild populations from Spain had aerial traits similar to those of the long-dormant, low-yielding subsp . falcata . Deep-crowned plants had greater plant diameter than shallow-crowned plants, and could be categorised into four distinct top-growth models according to their habit and vigour . One of these models combined spreading ability with high yield . The about 150 plants selected for their combination of deep crown, wide diameter, and good yield were characterised by a branch-rooted system . There was general correspondence between top-growth and root morphology of each model . Of the four deep-crowned models, three had rhizomes, with wide range of underground development and morphology, while the fourth had creeping roots . The latter model was the most rare among the examined accessions, never appearing in either cultivated or wild subsp . sativa . The implications of the results on the development of grazing-tolerant lucerne varieties are discussed .

Structuration of alfalfa genetic diversity using agronomic and morphological characteristics. Relationship with RAPD markers

“…[21,23,31,34]. The similarities of the morphology between the wild forms of both subspecies is likely to be the result of a convergent adaptation to escape selection pressure due to grazing, where the prostrate growth habit and the rhizomatous root system is favoured [7,17,28].…”

Breeding lucerne for persistence

“…Although another Italian report showed similar poor persistence results for the creeping-rooted trait, 'rhizomatous' genotypes were felt to be more persistent in comparison (Piano et al 1996). In follow-up research by the same group, it was concluded that it was the 'prostrate' types (with rhizomatous types found among these) that were the most grazing persistent types, and some 'semi-erect' types were reported to achieve a good balance between yield and grazing tolerance (Pecetti et al 2008). Similar results reported prostrate types, especially those with wide crowns, demonstrated the best tolerance under rangeland conditions in Northern Great Plains region of the USA (Berdahl et al 1989) and also under sheep grazing in Australia, but again, some tolerance could be found among upright, even winter-active, types in those studies (Humphries et al 2001).…”

“…1). Likewise, reselection and inter-mating of surviving plants after conducting the test with any base germplasm increased grazing tolerance in the selected populations as measured by procedures identical to the standard test (Smith and Bouton 1993;Humphries et al 2001;Pecetti et al 2008). The better survival of cultivars from this selection procedure under the three main management strategies, continuous stocking, rotational stocking, and hay cutting, also indicated its ability to increase general persistence via higher plant survival (Bouton and Gates 2003).…”

“…The trait lacked expression in most environments and was also found to be associated with low herbage yield further reducing its use in breeding (Busbice and Hanson 1969). Although another Italian report showed similar poor persistence results for the creeping-rooted trait, 'rhizomatous' genotypes were felt to be more persistent in comparison (Piano et al 1996). In follow-up research by the same group, it was concluded that it was the 'prostrate' types (with rhizomatous types found among these) that were the most grazing persistent types, and some 'semi-erect' types were reported to achieve a good balance between yield and grazing tolerance (Pecetti et al 2008).…”

Questions and avenues for lucerne improvement

“…Specific adaptation to definite exploitations depending on the morphological type emerged in breeding of grazing-tolerant lucerne. Germplasm of the M. sativa complex was classed into four types depending on its morphology and vigour (Piano et al 1996), and selections for each type were compared under different exploitation modes. Table 1 summarizes the results for two contrasting types, i.e.…”