Pollen-pollen interactions in Pinus sylvestris

Direct pollen-pollen interactions can influence pollen fertilization ability when pollen from different donors and origins germinate on the same flower. In this study, in vitro germination tests were used to study direct pollen-pollen interactions in Scots pine ( Pinus sylvestris L.). Pollen from southern (S, latitude 61degrees N) and northern (N, latitude 68degrees N) origins was germinated separately and in pairs at two temperatures (16 and 20degreesC), and pollen germination percentages and pollen tube lengths of the samples were analysed. The observed pollen performances of the two-donor pollen mixtures were compared with the mean performances of the pure pollen samples germinated in isolation. The significant difference between the observed and expected pollen performances indicated pollen-pollen interactions. Among SxS mixtures, only negative pollen-pollen interactions (= interference) were detected, while only positive interactions were found among NxN mixtures. Both types of interaction were substantially more frequent at the lower temperature. In general, direct pollen-pollen interactions during in vitro germination were rather infrequent and are not likely to have substantial influence on fertilization abilities in vivo in seed orchards or in natural forest stands of Scots pine. However, direct pollen-pollen interactions can be more pronounced among certain genotypes, which should be considered in artificial crossing experiments using pollen mixtures.