Diversity, genetic structure, distinctness and agronomic value of Italian lucerne (Medicago sativaL.) landraces

Eleven landraces belonging to the seven commercial ecotypes of northern Italy, and seven elite varieties, were evaluated with the aims of: (i) comparing landrace and variety germplasm for dry weight (DW, recorded across three harvests spanning over two years) and morphophysiological characteristics; (ii) estimating among-population (s(A)(2)) and within-population (s(W)(2)) genetic variances of landrace and variety germplasms; (iii) investigating the interrelationships among traits at the plant and the population levels; (iv) exploring patterns of phenotypic diversity, and the relationships between diversity and environmental variables at landrace collecting sites; and (v) assessing the distinctness of ecotypes. Some 256 or 512 genotypes per landrace, and 128 genotypes per variety, were grown in dense stand in an unreplicated design together with a replicated clone. Compared with varieties, landrace material showed higher total DW (+9%) and DW at the last harvest (+43%), lower (2.5-fold) summer mortality and autumn dormancy (P < 0.01), and similar winter mortality. Landraces exhibited a greater s(W)(2) value than varieties for all traits except autumn dormancy and number of florets per inflorescence (P < 0.01), with s(W)(2) always exceeding s(A)(2) (P < 0.01). The ratio of s(W)(2) to s(A)(2) averaged 23.1 for landraces and 6.5 for varieties across eight traits. Frequency of mowing at collecting sites was associated with higher total DW, better persistence, lower summer and winter mortality, larger leaflets and more stems per plant (r >= 0.66, P < 0.05). Cluster analysis showed that landraces geographically close or belonging to the same commercial ecotype tended to greater similarity. However, one landrace that evolved under very frequent mowing differed greatly from other landraces of the same ecotype. Based on discriminant analysis, two ecotypes may be sufficiently distinct for registration in a sui generissystem, even though they may not meet the criteria for registration under a homegenity requirement.