Rootstock Influence on Intra-clonal Variability in Spring Leaf Phenology of Pedunculate Oak (Quercus robur L.)

Abstract

This study aimed to investigate the influence of rootstock on intra-clonal variation in spring leaf phenology of pedunculate oak (Quercus robur L.) clones. In the context of clonal seed orchards, phenological synchrony is critical for successful pollination and seed production. While leaf phenology is largely under genetic control, increasing evidence suggests that rootstocks can influence scion phenology.
The experiment was conducted at the Brestje nursery using 43 pedunculate oak clones, each represented by three grafted ramets on genetically diverse seedling rootstocks. Phenological monitoring was carried out from 2010 to 2014, and intra-clonal differences in budburst timing (phenophase 3) were analyzed using bootstrap analysis. Additionally, the impact of a late spring frost in 2012 was assessed by comparing the timing of phenophase 4 between frost-damaged and frost-surviving ramets.
Results showed that, despite genetic uniformity, there was significant intra-clonal variability in budburst timing. In 2010, as many as 79.1% of clones exhibited a budburst range of ≥3 days between ramets, which can be considered a biologically meaningful threshold. The highest level of phenological synchrony was recorded in 2013. Notably, ramets that flushed later were less susceptible to frost damage, with the greatest observed difference between damaged and undamaged ramets being 21 days.
These findings highlight the critical role of rootstock in shaping scion phenology, particularly in the context of optimizing seed production and weather adaptability in clonal seed orchards.