Phenological Asynchronization as a Restrictive Factor of Efficient Pollination in Clonal Seed Orchads of Pedunculate Oak (Quercus robur L.)

The knowledge of the flowering biology of forest trees, and thus also of Pedunculate Oak, is exceptionally important when planning to mass-produce genetically high-quality seeds at clonal seed orchards (CSO) for the purpose of reforestation and restoration of forest cultures. The production of genetically high-quality seeds at CSOs, which assumes a high degree of genetic diversity, can only be guaranteed if 20 to 60 clones of different genotypes contribute to pollination (transferring of pollen from stamen to stigma). However, for a successful fertilization, which would guarantee the desired quality and quantity of seeds, phenological synchronization of the clone flowering within CSOs is also important. The beginning of pedunculate oak bud burst is under significant genetic control, which opens up the possibility to make the right selection of plus trees, with the goal of achieving a permanent phenological synchronization of flowering and flushing of clones with which the CSOs have been established. However, the effect of poor weather, such as heavy rainfall, too high or too low relative humidity of air, low temperatures, frosts, hail, etc., can sometimes disrupt favorable phenological synchronization of clones, also lowering the quality and quantity of seeds produced. The objectives of this study were (i) to determine the phenological synchronization of clone flowering within CSOs, (ii) to look into the possible effect of weather on the duration of receptivity of female flowers and pollen shedding, (iii) to determine the degree of correspondence between particular phenophases of flushing and flowering.The study has been conducted at the experimental field founded in the spring of 2008 within Rasadnik Brestje (Forest Administration Zagreb, Forest Office Dugo Selo). The experimental field has been founded by planting ramet in accordance with the experimental design of randomized section system with repetitions (sections). Each clone is represented with one ramet in each section. Ramets originate from the clones of pedunculate oak, from which clonal seed orchards were founded in the regions under respective Forest Administrations (FAs) Vinkovci (VK), Na ice (NA) and Bjelovar (BJ). Phenological observations of flushing and flowering were performed simultaneously, twice a week, until the leaves were fully developed on all clones, i.e. until all male flowers ceased to shed pollen or until all female flowers ceased to be receptive. The phenology of flushing was monitored in accordance with the methodology which distinguishes 7 phenophases in the flushing of pe