Provenance contribution to genetic composition of progeny from outbreeding seed orchard of Picea abies

The abundant flowering, observed in 2004 in a model outbreeding seed orchard established in Kórnik, Poland, promoted crossing between clones of five geographically distant populations of Norway spruce. The clones were selected from a group of ca. 1100 provenances participating in the international IUFRO 1964/68 experiment and performing best in terms of growth traits and adaptability. In the seed orchard, 91.3% of clones and 64.1% of grafts produced female and/or male strobili. Statistically significant differences between the clones were only found in the number of mature cones produced. The mean number of mature cones in individual clones was also significantly correlated with the latitude of the place of origin of maternal populations (r = 0.88, p = 0.047). The nearly equal percentages of clones representing each of the five populations in the outbreeding seed orchard (from 23.2 to 17.5%) resulted finally in the highly unequal production of full seeds by each population (from 62.9 to 0.7%). These data provide evidence to suggest that the level of genetic diversity in the progeny, expected from the number of growing clones, diverges from the level resulting from the contribution of clones to the full seed production which is an effective measure of the genetic composition of progeny. To avoid this divergence, an outbreeding seed orchard could be established with unequal proportions of clones from different provenances, considering the knowledge of their flowering phenology, and individual variation in flowering and cone production.