Effects of Red and Far-red Irradiation on Seed Germination in Betula verrucosa and B. pubescens

Abstract

Summary Effects of red (R) and far-red (FR) irradiation on germination of Betula pubescens and B. verrucosa seeds at the constant temperature of 24 °C have been studied using several seed lots. In most cases about 80 % of germinable B. verrucosa seeds germinated after one minute exposure to R light (4.24,µW cm -2 nm -1 at 660 nm) given after a 3 h dark imbibition. In B. verrucosa seeds 50 % germination was induced by R irradiation doses of 100 to 170 µW CM -2 nm -1 s within the intensity range of 4.24 to 0.64 ,µW cm -1 nm -1 . In seed lots of B. pubescens only a small part of the seeds responded to short periods of R irradiation, and most seeds required long irradiation periods (up to 48 h) irrespective of the intensity. The time required for completion of the phytochrome mediated step(s) for germination varied greatly between the individual seeds within all studied seed lots, but generally, however, longer periods were required in B. pubescens than in B. verrucosa seeds.