The effect of seed pretreatment and sowing date on the nursery emergence of Sitka spruce (Picea sitchensis [Bong.] Carr.) seedlings

Abstract

Sitka spruce seeds which had been: (1) untreated (U), (2) prechilled (P), or (3) prechilled and then redried and stored for 16 months (R), were sown into progressively warmer seed beds on four dates at monthly intervals from March to June. At each sowing date, samples of seed were germinated in the laboratory at optimum (20°C) and sub-optimum (10°C) temperatures. Prechilling and prechilling + redrying both increased the rate and total amount of germination compared with untreated seed at each test temperature. However in the nursery, the beneficial effects of pretreating Sitka spruce seed were restricted to sowing in March and April when soil temperatures were sub-optimal for the germination of untreated seeds. Pretreatment resulted in rapid seedling emergence at soil temperatures between 10°C and 15°C, whereas untreated seed germinated slowly and seedling emergence continued until high soil temperatures in June killed ungerminated seeds. The pattern of seedling emergence from the redried seed was similar to that from the prechilled seed, except for a lag in the start of seedling emergence probably due to the extra time needed for redried seed to imbibe water in the seed beds. Thus redrying caused insignificant loss of seed performance on the nursery. Seed sown in May and June experienced average temperatures close to the optimum for germination of 20°C, however daily maxima regularly exceeded 35°C resulting in the cessation of seedling emergence in all three seed treatments, and the loss of newly emerged seedlings. Periods of warm weather from June onwards were the main factors limiting the final number and size of seedlings.