Genetic worth and diversity across 18 years in a Nordmann fir clonal seed orchard.

• Context: Many tree breeding programmes rely entirely on clonal seed orchards as the link between breeding activities and forestry, and are thereby also exposed to yearly fluctuations in the orchard crops. • Aims: The main objective was to study the impact of year and clone fluctuations in strobili production on genetic worth, as well as on genetic diversity, of 18 consecutive commercial seed orchard crops. • Methods: In a mature Abies nordmanniana clonal seed orchard, a yearly visual assessment of female and male strobili was carried out on a total of 18 clones (260 ramets), and coupled with clone breeding values. • Results: Despite large annual and clone variation, and year-by-clone interaction in strobili production, the orchard's genetic worth was somewhat uniform when considering four evaluated traits in the 11 years of superior or medium crop size. These years accounted for 95% of the accumulated cone crop over the whole period (18 years). Noteworthy deviations were only seen in the seven poorest seed years, comprising the remaining 5% of the total cone crop, where genetic diversity measures were also low. • Conclusion: Avoiding small crop years seems to be a reasonable way to avoid fluctuations in the commercial seed orchard product. [ABSTRACT FROM AUTHOR]