Plant breeding programmes frequently face the dilemma whether to breed for wide or specific adaptation. This is especially true for forage crop breeding, whose genetic resources may largely include landraces that are adapted to specific growing conditions. This study aimed to (1) investigate the extent and pattern of genotype × location (GL) interaction for biomass yield of recent lucerne cultivars across organically-managed sites of Northern and Central Italy and its relationship with cultivar selection environments, (2) provide an empirical assessment of yield gains derived from specific-adaptation and wide-adaptation breeding strategies, and (3) identify top-performing cultivars for different geographic regions. Cultivar adaptive responses, modelled by additive main effects and multiplicative interaction analysis, displayed wide GL interaction of cross-over type across test sites that reflected remarkably the geographic area and/or the growing conditions (particularly for extent of summer drought) of their selection environment. GL interaction patterns suggested three putative subregions to breed for specific adaptation, namely, Northern Italy north of the Po river, Northern Italy south of the Po river, and Central Italy. Growing specifically-adapted cultivars provided an estimated average advantage of 12.9% across subregions relative to the best-performing widely-adapted cultivar. Yield gains of recent top-performing material over an historical, widely-adapted cultivar indicated that selection for specific adaptation would provide 3.2-fold greater yield gain averaged across subregions, and 3.4-fold greater yield gain over the target region when weighting yield gains on the putative proportion of the target region of each subregion, compared with selection for wide adaptation.
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