No abstract

The effects of clonal variability, crown position of cones, and top pruning on the proportions of viable outcrossed progeny [Formula: see text] and filled seeds (PF) were investigated in a 20-year-old Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seed orchard. Estimates of [Formula: see text] were derived by means of a maximum likelihood procedure from data from 10 allozyme loci. Values for [Formula: see text] and PF were significantly heterogeneous (P < 0.05) among six selected clones for all pruning treatment x clone combinations. On the average, estimated values for [Formula: see text] and [Formula: see text] were greater in seeds collected from the upper crown [Formula: see text] than from the lower crown [Formula: see text]. Combined over crown positions, pruning appeared to have little effect on [Formula: see text], although the proportion of filled seeds was slightly lower in pruned ramets [Formula: see text] than in unpruned ramets [Formula: see text]. The overall frequency of viable selfs [Formula: see text] in the progeny of the six clones was 0.08.

Post-storage water relations, stomatal conductance, and root growth potential were examined in ponderosa pine (Pinus ponderosa Dougl. ex Laws.) seedlings from high- and low-elevation seed sources that had been lifted either in October or November and freezer stored, or in March, and then grown hydroponically in a greenhouse for 31 days. Seedlings lifted in October had poor root initiation (< 17 new roots per seedling), low predawn leaf water potentials (< -1.5 MPa), and low stomatal conductance (7.10 mmol m(-2) s(-1)) compared with seedlings lifted in November or March. There was little difference in post-storage water relations and stomatal conductance between seedlings lifted in November and those lifted in March. Throughout the 31-day test, seedlings from the high-elevation seed source produced 3-9 times more new roots, had higher predawn leaf water potentials (-0.6 to -0.7 MPa versus -1.1 to -1.6 MPa), and 1.3-5 times greater stomatal conductance than seedlings from the low-elevation seed source. For all seedlings on Day 31, the number of new roots was significantly related to predawn leaf water potential (r(2) = 0.65) and stomatal conductance (r(2) = 0.82). Similarly, the dry weight of new roots per seedling on Day 31 accounted for a significant amount of the variation in predawn leaf water potential (r(2) = 0.81) and stomatal conductance (r(2) = 0.49).

Seedlings from nine Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seed sources were top pruned at six nurseries in the Pacific Northwest and then planted at field sites in their own seed zones and on one common site. Seedlings pruned tall (25 cm) and early in the growing season flushed again about 5 weeks after pruning and set bud 2 weeks later than unpruned controls. Nursery yield (number of shippable seedlings) was the same for tall–early pruned and control seedlings; however, pruning increased the number of seedlings with multiple leaders from 10 to 38%. Pruned seedlings were smaller than unpruned seedlings in height, stem diameter, bud length, and root and shoot weights at the time of field planting. First-year field survival and growth were the same for pruned and unpruned seedlings at all planting sites. Second-year field growth of pruned seedlings was generally greater than that of unpruned seedlings, and frequency of multiple leaders was reduced. However, pruned seedlings were still shorter than unpruned ones after 2 years. Field growth was greater when seedlings were pruned early rather than late (end of growing season) and tall rather than short (15 cm). Late–short pruning yielded shorter seedlings with smaller terminal buds and should be avoided. If pruning benefits nurseries by expediting grading, handling, and planting and, perhaps, enhancing growth later in the field, it should be continued as a cultural practice. However, longer-term measurements are needed for assessing the full effect of pruning on seedling growth.

Application.To ensure that freezer storage will satisfy chilling requirements in fall-lifted ponderosa pine, seedlings should be harvested late in the fall. Lifting seedlings too early in the fall may result in poor shoot development after planting and may delay budbreak even into the second year.Abstract. The degree to which freezer storage fulfilled the chilling requirement of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) seedlings of two sources was determined by monitoring their development after potting or planting. The seedlings were lifted in September, October, November, or March and subjected to storage before outplanting. The fulfillment of chilling was assessed by measuring days to budbreak, cumulative percentage of seedlings flushing, foliated shoot length, and rate of bud abortion. The effect of freezer storage depended on stage of seedling development at lifting, length of storage, and seed source. Storage did not totally replace winter conditions, especially for seedlings lifted in September and October. Those from a high-elevation seed source flushed sooner than those from a low-elevation source. Delayed budbreak after planting of early lifted seedlings from the high-elevation source disappeared in the second year, but those from the low-elevation source continued to show effects. Seedlings lifted and stored in November had patterns of budbreak that were similar to those of seedlings that had overwintered in beds.