FACTORS AFFECTING SEED SET IN DOUGLAS-FIR (PSEUDOTSUGA-MENZIESII)

Cone and seed development in Douglas-fir were studied from pollination until seed release in 1986. Cone abortion at, and shortly after, pollination was high, resulting from a combination of low temperatures and possibly high moisture and populations of microorganisms on cones. Seed potential averaged about 75 seeds per cone with 31 filled seed per cone, giving an average seed efficiency of 39%. The major loss of seed resulted from insufficient pollen in the ovules. Other causes were ovule and embryo abortion at various stages of development. The effects of prezygotic and postzygotic events on seed set are discussed with respect to the reproductive success of Douglas-fir.