Pre- and post-pollination polyhouse environment effects on pollen and seed development in potted Piceaengelmannii grafts

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Abstract
Potted Picea engelmannii grafts were moved as reproductive buds began to swell in spring from outdoors into an open, closed, or heated polyethylene-covered house in which day to night temperatures through the completion of pollination averaged 10:5, 14:6, and 24:18.degree.C. Although increasing polyhouse temperature accelerated pollen shedding by 21 days, this was accomplished by an increased proportion of underdeveloped plots rotted pollen cones (53 to 86%) and decreased yield of pollen per cone (74 to 22 .mu.L). Following pollination grafts were moved from the heated to the open house, and half of those originally in the open and closed houses had their environments switched. Higher polyhouse temperatures during the prepollination period also initially accelerated, and then progressively retarded, the growth of seed cones. Seed cone survival was uniformly high (91-97%) in all treatments. However, cones from the heated/open house treatment were 27% shorter, weighed 59% less, and contained 39 and 88% fewer total and filled seeds, respectively, than cones from the open/open house treatment. Cone development was also adversely affected by heat during the postpollination period. the weight (3-3.2 mg) and germinative capacity (82-95%) of filled seeds were independent of polyhouse treatment. Practical implications for the management of P. engelmannii in indoor-potted orchards are discussed.