Genetic Variation in Growth Traits in a Quercus robur L. Open-Pollinated Progeny Test of the Slavonian Provenance

The study presents evaluation of an open-pollinated progeny test of 21 selected plus trees from Slavonian pedunculate oak provenance in Croatia (in the central part of Drava river valley). The test was established in 1992 with two-year-old seedlings. Heights were measured at 5 to 13 years and diameters at breast height (DBH) at 10 to 13 years after sowing. Variances caused by the population within provenance effect were not significant during the studied period. In contrast, variance components caused by family effect were statistically significant, and ranged from 11.1 to 18.6% and from 2.2 to 10.6% for height and DBH respectively. Statistically significant variances caused by the family effect indicate that most of genetic variation of productive traits was within the studied populations. The estimated family mean narrow sense heritabilities varied from 0.62 to 0.78 and from 0.28 to 0.65, while individual heritabilities ranged from 0.48 to 0.80 and from 0.09 to 0.46 for height and DBH, respectively. Realised gain from the test and expected genetic gains by two possible methods of selection for the measured traits have been calculated for: i.) realised gain i.e. superiority of selected plus trees progenies over control plants (bulks from unselected trees within the provenance) ii.) individual within provenance mass selection of first generation plus trees at the same ages as those represented in studied trial and iii.) backward selection among first generation plus trees after open-pollinated testing. Estimated genetic gains indicate that the highest gain could be expected by backward selection among first generation plus trees after open-pollinated progeny testing (9.7 to 22.3% and 6.8 to 17.3% over control means). These results indicate that due to significant within population variation and high additive variances, improvement for productive traits in the studied oak populations could be achieved by use of seeds and plants from selected plus trees (especially from already established clonal seed orchard), at least in younger ages.