CONE AND SEED DEVELOPMENT IN A WIND-POLLINATED, WESTERN HEMLOCK (TSUGA-HETEROPHYLLA) CLONE BANK

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. 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 yr, respectively. In 1983, 98% of the clones bore a pollen-core crop compared with 53% in 1986. Lack of fertilization resulting from a limited pollen supply was 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 12 and 14%, respectively. The full-sized but empty seed resulted from lack of fertilization and embryo degeneration. -from Authors