Effects of temperature, moisture content and storage on dormancy release and germination of European hornbeam (Carpinus betulus L.) seeds

Mature seeds of European hornbeam (Carpinus betulus L.) are characterized by deep physical and morphological dormancy. Although a procedure for their stratification is well developed, secondary dormancy prevents many healthy seeds from germinating, and this affects the productivity of the specie's nursery material. The objective of this work was to determine optimal conditions for germination of European hornbeam seeds, and how to avoid the induction of their secondary dormancy. We also aimed at establishing methods for controlling the seed germination prior to sowing. Harvested nuts were stratified in a substrate at 20 degrees/3 degrees C for 4 + 16-18 weeks. Following stratification, the seeds were dried up to 25, 20, 15 and 10 per cent moisture content or frozen in the substrate at -3 degrees C for 8, 16 or 32 weeks. The seeds dried up to 10 and 15 per cent moisture content were also stored at -3 degrees C for 8, 16 and 32 weeks. After stratification, drying, storing and freezing, the seeds were germinated at the laboratory at 20 degrees C and 3/20 degrees C (16 + 8 h). However, reliable germination results were only achieved when the seeds not germinating at the above listed temperatures were additionally germinated at 3 degrees C. Poor germination at 20 degrees and 3/20 degrees C was due to the induction of secondary dormancy. Stratified seeds of European hornbeam were found sensitive to dehydration. Their viability decreased considerably, particularly after drying up to 10 per cent moisture content, and in the seeds dried to 15 per cent the viability further decreased during storage. The seeds that were not dried but frozen at -3 degrees C after stratification retained their germination ability for at least 16 weeks. Our results shows dual effects of temperature on germination control of hornbeam seeds. In laboratory practice applying temperature cycles of 3 degrees/20 degrees C at 16/8 h intervals is recommended to avoid the induction of secondary dormancy.