The two white spruce seed sources used in this study were chosen to represent the south and north of the large commercial forest zone in Québec. They came from two first-generation seed orchards (SO1-1 and SO1-5) commonly used for reforestation in Québec, Canada (Fig. 1), distant from each other by 550 km and 2.2° of latitude (Table 1). They are clonal seed orchards made of grafted plus-trees that were selected in local natural stands. They each pertain to one of the two broadly defined white spruce breeding zones in Québec, Canada, which differ mostly in latitude and associated mean annual temperature (Li et al., 1997). Orchard SO1-1 represents the southern seed source and SO1-5 the northern seed source (Fig. 1). Open-pollinated seeds were collected in each seed orchard for two consecutive years (2008 and 2009) and mixed, making up one seedlot per seed orchard. Seedling production was conducted under nursery conditions at the Pépinière forestière of Saint-Modeste (Québec, Canada, 47°50′ N, 69°30′ W) and subjected to standard cultural practices during two consecutive growing seasons (Lamhamedi et al., 2006; Villeneuve et al., 2016).