Tomato Seed Germination. Osmotic Pretreatment and Far Red Inhibition

At 25 °C germination of tomato (Lycopersicon lycopersicum) seeds is inhibited by continuous and intermittent far red illumination. It is also inhibited by a single 30 min far red irradiation given 8 h from the start of imbibition. The incubation of seeds in a mannitol solution inhibitory for germination has no effect on the final germination percentage after seeds are subsequently transferred to water. A 30 min far red irradiation at the time of transfer results in partial inhibition of germination. This inhibition can be released by the continuation of osmotic incubation for several days before the transfer to water. At the end of a 7 d dark period of osmotic incubation, inhibition of subsequent germination in water can be realized only by continuous far red illumination. Seeds osmotically pretreated for 7 d and afterwards dried-back show a mean time to 50% germination significantly lower than that of untreated seeds. Moreover, besides single and intermittent, even continuous far red light has no inhibitory effect on the germination of these seeds. It is concluded that, in addition to the already known germination advantages, osmotic presowing treatment also induces the ability of seeds to germinate under unfavourable light conditi.