Dormancy induction in coastal Douglas-fir seedlings: bud development, dormancy development, and dry-matter allocation
Date
2018-06-21
Authors
MacDonald, Joanne Elizabeth
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Abstract
Bud development under controlled environment conditions in coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) seedlings was investigated. Eight dormancy induction treatments varied type of short day (SD), temperature and moisture. Photoperiod was decreased to 8 h either abruptly (ASD) or gradually (GSD). Day/night temperature was either constant at a high temperature (HT), or gradually decreased to a low temperature (LT). Moisture was controlled to either result in no drought-stress (ND) or to cause drought-stress (D). Once the dormancy induction signal was perceived by seedlings, neoformed-leaf initiation stopped and bud development began. Bud development involved two
stages of primordial initiation (bud-scale and preformed-leaf) separated by a
transitional phase. The change from neoformed-leaf to bud-scale initiation was faster under ASD than under GSD, under HT than under LT, and under D than under ND. Bud-scale-complex development was faster under ASD than under GSD. Type of SD had a significant influence and moisture had a weakly significant influence on number of bud scales initiated. Fewer bud scales were initiated under ASD than under GSD and under ND than under D. The transitional phase was
shorter and hence preformed-leaf initiation started earlier under ASD than under
GSD and under ND than under D. Type of SD, temperature, and moisture had a significant influence on number of preformed-leaf primordia initiated. More
preformed-leaf primordia were initiated under ASD than under GSD, under HT
than under LT, and under ND than under D. Anatomy of the bud-scale receptacle and crown region were distinctly different between ASD and GSD. Crown height
was greater under ASD than under GSD. Crown width was greater under ND than
under D.
Bud development, dormancy development, and dry matter allocation under commercial greenhouse conditions in coastal Douglas-fir seedlings were investigated. There were 3 dormancy induction treatments: SD without moisture stress (SD$-$MS), SD with moisture stress (SD+MS), and long day with moisture stress (LD+MS). The MS occurred during the first 2 weeks of SD+MS and LD+MS. There were 4 durations in SD: 3, 4, 5 and 6 weeks in SD (WK SD).
Within the first week in SD, neoformed-leaf initiation ended, bud-scale initiation began and ended, and rapid preformed-leaf initiation began. Rapid preformed-leaf initiation was completed by week 6, and slow preformed-leaf initiation was completed by week 10 for 6 WK SD and week 13 for 3, 4, and 5 WK SD. Number of leaves initiated ranged from 134.9 to 175.3. Duration in SD had a highly significant effect on number of preformed leaves initiated; significantly fewer leaves were initiated under 6 WK SD than under 3, 4, and 5 WK SD. As preformed-leaf initiation ended, mitotic index (MI) approached zero. After over-wintering,
buds flushed 4.6 to 6.9 days after being placed under forcing conditions in March. Duration in SD had a highly significant effect on speed of bud break. Buds from 4 WK SD$-$MS flushed significantly faster than those from other SD$-$MS treatments; buds from 4 WK SD+MS flushed significantly faster than those from 3 WK SD+MS. Shoot diameter at the root collar and root dry weight ranged from 3.1 to 3.5 mm and 0.55 to 0.73 g, respectively. Duration in SD had a highly significant effect on root collar diameter. Root collar diameters of seedlings from 3 and 4 WK SD were significantly larger than those from longer durations in SD. There was a
highly significant moisture regime x duration in SD interaction for root dry weight.
Within the first week of LD+MS, neoformed-leaf initiation ended and bud-scale initiation began. After 3-4 weeks, bud-scale initiation ended and slow preformed-leaf initiation began. Rate of preformed-leaf initiation was slow until week 6, rapid during weeks 8-10, and then decreased slightly between weeks 10-13. Number of preformed leaves initiated averaged 159.4. By week 13, as preformed-leaf initiation slowed, MI was decreasing, but was not approaching zero. After overwintering, buds flushed 11.0 days after being placed under forcing conditions in March. Root collar diameter and root dry weight were 3.2 mm and 0.62 g, respectively.
Both studies demonstrated that the sequence of stages in bud development is
constant, but the phenology and characteristics of the stages vary with type of
dormancy induction treatment. The relationship between bud development, mitotic
activity of the apical meristem, dormancy development, and speed of bud break is
presented and discussed. Terminology which better describes the active processes
of dormancy induction and dormancy development is suggested. Recommendations
concerning the use of SD for early dormancy induction in commercial greenhouse
culture are made.
Description
Keywords
Douglas fir, Seeds, Dormancy, Seedlings, quality