Effect of storage on pollen viability in Pinus sylvestris L., Pinus mugo Turra and their hybrid swarms

Pollen storage is the only way how to overcome the differences in phenology of forest trees and geographically determined reproductive barriers between them during controlled pollination. Pollen viability of Scots pine (Pinus sylvestris L.), mountain dwarf pine (P. mugo Turra) and their hybrid swarms was evaluated after 3-years storage at −20°C using in vitro germination test. One population of each P. sylvestris and P. mugo were involved into study along with three hybrid swarms. Germination potential of the stored pollen grains was reduced significantly in comparison with freshly collected pollen. Profound decrease in germination rate was recorded in the two hybrid swarms (4.0–4.7%), less profound in the remaining three populations (0.6–2.4%). Pollen tube length, as the second pollen viability trait was reduced in stored pollen grains in a larger extend ranging between 51.4% and 54.3%. The pollen grains of the species P. mugo was exception in this respect yielding pollen grains whose growth was retarded of 21.9% only. Analysis of variance confirmed significant differences between fresh and stored pollen grains. Statistically significant were also the differenc- es between compared populations and between tested individuals of the respective populations