Effects of accelerated pollen-cone development on pollen cytology and fertilizing potential in western hemlock (Tsuga heterophylla)

Western hemlock (Tsuga heterophylla (Raf). Sarg.) pollen cones on cut branches were collected at different stages of development and maintained at room temperature in flasks of water to accelerate pollen-cone development and produce forced pollen. Accelerating pollen-cone development at early developmental stages reduced the number of cones that matured, decreased the quantity of pollen produced, increased the proportion of abnormally developed pollen and reduced the fertilizing potential of the pollen, as determined by seed efficiency. If the branches were collected after the pollen cones were at least 50% emerged beyond the bud scales, pollen-cone development could be successfully accelerated without decreasing pollen yield or fertilizing potential. Pollen collected from cones which were accelerated at early stages and stored for two years had a lower fertilizing potential and produced fewer seeds per cone than either unstored pollen or stored pollen collected from cones accelerated at later stages of development. The feasibility of accelerating pollen-cone development to ensure adequate supplies of pollen for controlled crosses or supplemental mass pollination is discussed.