Genetic ranking of potato varieties is different in Scandinavian and Mediterranean environments

Understanding genotype-by-environment interactions (G×E) in potato is critical for selection of cultivars well adapted to specific environments. Using a unique dataset and pedigree information from a breeding program for tetraploid potato genotypes grown under Scandinavian and Mediterranean environments, this research investigates the G×E interaction phenomenon occurring within country and between countries, where Scandinavia and Mediterranean areas were defined as mega-environments.The dataset consisted of ~ 13,000 potato breeding lines with phenotypic data spanning 17 years that were evaluated in different locations in Denmark (DK), Spain (ES), and Morocco (MO). A mixed model that used the pedigree-based additive relationship matrix to account for covariance among lines, was fitted for yield, tuber size, and scab disease. We estimated variance components and heritabilities for each trait within each environment as well as the additive genetic correlations among traits measured in different mega environments. Due to limited data for tuber size and scab, data from ES and MO was combined and considered as one Mediterranean mega environment.We found highly significant G×E interactions for yield and scab expressed in different mega environments. The indications of G×E interactions included the lack of unit genetic correlation between trait expression in different mega-environments, heterogeneous genetic variances and different heritability for traits expressed in different mega-environments. Specifically, the additive genetic correlations for the yield trait were 0.5 between DK and ES, 0.6 between DK and MO, and 0.8 between ES and MO. The correlation was 0.6 between DK and ES & MO for scab when ES and MO were combined. At the same time, the additive genetic variance of yield expressed in ES was > 2 times higher than the yield variance in DK and MO. In contrast, the additive genetic variance of scab in DK was higher than that of scab expressed in the combined ES & MO environments. G×E interactions for tuber size trait was smaller as the genetic correlation between DK and combined ES & MO tuber size was 0.8, and the differences in genetic variance or heritability was not significant between mega environments. In addition, significant G×E interactions within mega-environments were found. For exmple, genotype × year, genotype × location and genotype × year × location interactions collectively contributed about 17.7% to the total variance of the yield trait expressed in DK. The percentage was 16.8% and 26.9% for ES and MO, respectively, highlighting the considerable effect of G×E interactions within mega-environment on yield. These G×E interactions had lower effects on scab traits (14.6–20.9%) and tuber size (12.5–15.3%).In conclusion, due to environmental differences between Scandinavian and Mediterranean regions, re-ranking of breeding values is significant for important production traits in potato. Thus, prediction of breeding values for each specific target mega environment will be more beneficial in potato breeding than selection for performance across mega environments. Therefore, prediction of breeding values for Mediterranean environments should be developed at an early state in the breeding program before lines with high potential are moved to the Mediterranean area for further testing.