Breeding gain from exploitation of regional adaptation: An alfalfa case study

Exploiting genotype × environment interaction (GEI) by specific selection for well‐defined subregions could contribute to more productive and sustainable cropping systems. This case study aimed to verify this hypothesis by assessing actual genetic gains from phenotypic and genotypic selection for alfalfa ( Medicago sativa L.) biomass yield in two subregions of northern Italy with contrasting GEI pattern (subregion A, featuring sandy‐loam soil and no summer drought as a result of irrigation; subregion C, featuring silty‐clay soil and summer drought resulting from rainfed cropping). Selection and test environments were mainly represented by four managed environments created by the factorial combination of the relevant soil types and drought stress levels. Genotypic selection depended on yield responses of 90 half‐sib families in the environment representing each subregion (specific adaptation) or across these environments (wide adaptation); phenotypic selection for wide or specific adaptation was stratified for single plants in different environments. Half‐sib family data indicated modest genetic correlation between subregions ( r g = 0.56). Biomass yield data of six selections and six cultivars or landraces providing their genetic base revealed at least twofold greater yield gains for specific adaptation over wide adaptation for phenotypic or genotypic selection, with a minimum within‐subregion advantage of 43%. On average, genotypic selections displayed over 10‐fold greater yield progress than phenotypic selections. Adaptation strategies had negligible impact on seed yield and leaf‐to‐stem ratio of the selections. Experiment data from seven agricultural environments highlighted the importance of breeding for specific adaptation to achieve yield progress over locally top‐performing commercial varieties. Circumstances that support a specific‐adaptation strategy were discussed.