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. Key words: Douglas-fir, seed set, cone, ovule, development, abortion.
The effects of self-, cross-, and no pollination on cone size, filled seed, pollination efficiency, ovule development, and seed efficiency were tested on rooted ramets of six western red cedar (Thujaplicata Donn) clones. To fully develop, ovules must be pollinated with viable pollen and cones must have a minimum of one developing seed. The seed potential was constant among clones and not affected by pollination. The greatest loss of potential seed resulted from a failure of ovules to be pollinated, followed closely by the low percent viability of pollen. Unpollinated ovules aborted at the megaspore or free-nuclear stages. Pollinated ovules may abort at any stage of development, but it was most common during the long free nuclear stage. Selfing had a limited effect on postzygotic loss owing to embryo abortion or on seed set. Western red cedar is well adapted for a high degree of selfing. Clonal differences occurred in seed efficiency and stages at wich seed losses were most commun. Seed set in western red cedar may be increased if cones on female parents having a history of high seed efficiency are pollinated several times within a 1 week peak pollination period with abundant pollen of known high percent viability. Potential seed losses are discussed with reference to pollination and ovule development.
Seed orchard production of Chamaecyparis nootkatensis (D. Don) Spach seed faces several challenges including low seed production, pollen-cone abortion, self-pollination, and accelerated reproductive development. In a seed orchard study in 1988 and 1989, approximately eight seeds were produced per cone, but only one to three seeds per cone contained viable embryos. Pollen-cone abortion in 21 clones ranged from 6 to 87% in 19891990 and from 0 to 6% in 19901991. A bud mite, identified as Trisetacus chamaecypari Smith, was consistently associated with pollen-cone abortion in two orchard locations. This mite may be the cause or simply a symptom of unhealthy pollen cones. In a pollination study involving wind, self, and cross pollinations on five clones, self-pollinated cones had significantly fewer seeds containing embryos (4%) compared with the other treatments (2833%). Pollen-cone development at a seed orchard occurred in July and August 1990 and was comparable with natural stand phenology. However, embryo development was significantly accelerated, with embryos at a seed orchard substantially larger than embryos at the natural stand at comparable times.
Seed and seed-cone development were observed in a wind-pollinated western hemlock (Tsugaheterophylla (Raf.) Sarg.) clone bank in 1983 and 1986. Seed efficiency, the number of filled seed per cone divided by the seed potential, averaged 64% for 58 wind-pollinated clones in 1983 and 20% for 38 clones in 1986. Based on anatomical observations and cone dissections, seed losses resulted from pre- and post-pollination ovule abortion, insufficient pollen, no fertilization, and embryo degeneration. Prepollination ovule abortion, identified by small, flat seed in mature cones, contributed to 11 and 14% reduction in filled-seed yield in 1983 and 1986, respectively. Full-sized but empty seed (lacking an embryo) accounted for 25 and 66% reduction in potential seed yield in the 2 years, respectively. In 1983, 98% of the clones bore a pollen-cone crop compared with 53% in 1986. Lack of fertilization resulting from a limited pollen supply was believed to be the main cause for the lower filled-seed yield in 1986. The effect of wind and controlled (cross-) pollination on filled-seed production was determined for 16 clones in 1983. Seed efficiency after wind and cross-pollination averaged 65 and 69%, respectively. Seed potential averaged 34 and 31 ovules per cone for the wind- and cross-pollinated cones, respectively. Prepollination ovule abortion averaged 12 and 14%, respectively. From anatomical observations, the full-sized but empty seed resulted from lack of fertilization and embryo degeneration. The different factors affecting final filled-seed yield are discussed in terms of their effect on seed production.
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