Dormancy Induction Treatments Research Articles

Application of the hydrotime model to assess seed priming effects on the germination of rapeseed (Brassica napus L.) in response to water stress

Our aim was to determine whether the parameters of the hydrotime model can be used to compare the effects of seed priming treatments on germination. Seeds of three rapeseed cultivars (‘H61’, ‘H4815’, and ‘DK003’) were exposed to priming treatments and then their germination was tested at different water potentials. Seed priming improved the germination percentage, which was higher in ‘H4815’ than in the other two cultivars, and it increased germination rate (decreased θH) and uniformity (decreased σψb). The increase in germination rate was higher in PEG-osmoprimed than in NaCl-osmoprimed and hydroprimed seeds. The base water potential allowing 50% germination ([Formula: see text]) also was affected by seed priming, but the response of cultivars to different priming treatments varied. Compared with the control seeds, hydropriming of ‘H61’ seeds shifted ψb(50) toward negative values, whereas NaCl-osmopriming of ‘H4815’ seeds shifted ψb(50) toward negative values. On the other hand, priming of ‘DK003’ seeds shifted ψb(50) to more positive values and increased susceptibility to water stress. After dormancy-breaking and dormancy-induction treatments, ψb(50) shifted to more negative or positive values, indicating the release of primary dormancy and induction of dormancy, respectively. Therefore, priming treatments should be selected, depending on the environmental conditions anticipated to prevail during the germination of rapeseed seeds.

Standardization of Dormancy Induction Treatments in Groundnut cv. TMV 7

Standardization of Dormancy Induction Treatments in Groundnut cv. TMV 7

The effect of short day treatments on containerized Douglas-fir morphology, physiology and phenology

The effect of short day treatments (‘blackout’) on Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) container seedlings at the time of lift and following cold storage was investigated. Variables measured included height, root collar diameter (RCD), root growth capacity (RGC), photosynthetic efficiency after −18 °C freezing (PEF), and days to terminal bud break (DBB). From one to four blackout dormancy induction treatments were started on three dates (July 12, July 26, and August 10) with 10 or 20 d between multiple blackouts. Increasing the number of blackout treatments resulted in lower RCD, lower DBB in the late winter/early spring, and higher PEF in the early fall. Later blackout start dates decreased PEF in the early fall, and increased overall height and late fall RGC as compared to earlier blackout start dates. Nurseries growing Douglas-fir seedlings from coastal Pacific Northwest provenances should be aware that blackout regimes can decrease RGC in the late fall, and cause quicker dormancy release in the early spring. Coastal Douglas-fir can be lifted and planted in the early fall, when RGC and DBB are relatively high. If planting between February and April is necessary, seedlings given blackout should be cold stored in January to maintain an adequate level of dormancy, RGC and PEF.

Inflence of dormancy induction treatments on the photosynthetic response of field planted western hemlock seedlings

Nursery cultural treatments can improve field performance by pre-acclimatizing seedlings to field site conditions. Four dormancy induction treatments (DIT) (i.e. long-day wet, long-day dry, short-day wet, and short-day dry) were examined for their influence on net photosynthesis ( P n) of western hemlock ( Tsuga heterophylla (Raf.) Sarg.) seedlings. Seedlings were planted on a control site with high soil water potential, adequate nitrogen levels and no plant competition. Net photosynthesis was measured in response to a full range of photosynthetically active radiation (PAR) and vapour pressure deficit (VPD) conditions on 1-year-old and current-year needles. The response of P n to both PAR and VPD was defined by response surface models used to forecast field performance over the range of anticipated environmental conditions. All models had greater P n values as PAR increased, but increased VPD resulted in a suppression of P n. For 1-year-old needles, short-day compared with long-day seedlings, had greater or equivalent P n response over the range of measured PAR and VPD conditions. For current-year needles, short-day treated seedlings had greater P n response at high VPD (e.g. 3.8 kPa). Current-year, compared with 1-year-old needles had from 45 to 110% greater P n over a wide range of PAR (0.5–2.2 mmol m −2 s −1) and VPD (0.5–2.4 kPa) conditions. The results were compared with the testing of these DIT on a reforestation site to determine the validity of measuring physiological responses on a control site as a method for improving nursery cultural treatment selections.

Effect of nursery culture on morphological development of western hemlock seedlings during field establishment. I. Flushing, shoot elongation, and bud development

Western hemlock (Tsugaheterophylla (Raf.) Sarg.) seedlings grown in two different container cavity sizes that received four different dormancy induction treatments, short (SD) or long days (LD), in combination with moisture stress (D) or no moisture stress (W), in the greenhouse, and lifted and placed in cold storage (November, January, or March) were planted on two adjacent coastal reforestation sites on Vancouver Island, British Columbia, and monitored for phenological responses during the first growing season. The SD seedlings flushed sooner and began bud development later than the LD seedlings, although the effect on flushing was small for those lifted in March. Moisture stress and SD together in the greenhouse reduced shoot elongation rates but had little impact on field bud development. Cold storage of seedlings lifted in November and January delayed flushing, reduced shoot elongation rates, and advanced bud development compared with the March-lifted stock. The influence of cavity size was generally small on most variables measured. Shoot elongation was slightly faster on the southeast site than on the northwest site, whereas bud development was more rapid on the northwest site. The effect of site on date of flushing varied with nursery treatment.

Effect of nursery culture on morphological development of western hemlock seedlings during field establishment. II. Survival, shoot length components, and needle length

Western hemlock (Tsugaheterophylla (Raf.) Sarg.) seedlings grown in two different container cavities that received four different dormancy induction treatments, short (SD) or long days (LD) in combination with moisture stress (D) or no stress (W) in the greenhouse, and lifted and placed in cold storage (November, January, or March), were planted on two adjacent coastal reforestation sites in British Columbia and monitored for survival and morphological development. Survival was greatest in seedlings grown in the larger cavities in the greenhouse, in seedlings lifted in March, and in seedlings not treated to moisture stress. Seedling shoots had more stem units on the southeast than the northwest site, but the amount varied with nursery treatment. Seedlings from the LD treatments produced more stem units during free growth and lammas growth than those from the SD treatment. Nevertheless, most shoot growth was predetermined in the buds during nursery culture, accounting for a minimum of 67% of the final number of stem units. Stem unit length (SUL) was longer in seedlings on the southeast site than on the northwest site for those treated to LD in the nursery. Seedlings treated to short days showed the reverse pattern (SDW) to this, or were unaffected by site (SDD). Shoots and needles were shortest for seedlings from the SDD treatment and for those lifted in November. Shoot growth was greatest for seedlings lifted in March and for those treated with LD, mainly owing to their longer SUL. Lammas growth was most frequent in seedlings from the smaller cavities, and in those from the November and March lifts.

Bud development in coastal Douglas-fir seedlings in response to different dormancy-induction treatments

Bud development in response to different dormancy-induction treatments in coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) seedlings was investigated under commercial greenhouse conditions. There were three treatments: short day without moisture stress, short day with moisture stress, and long day with moisture stress. Within the first week in the short day treatments, neoformed-leaf initiation ended and bud-scale initiation began and ended. Rapid leaf initiation began in week 1 and was completed by week 5 for the short day with moisture stress treatment and week 6 for the short day without moisture stress treatment. Slow leaf initiation was completed by week 13. Crown cells became apparent within the pith during weeks 3–6; cell walls thickened between weeks 8 and 13. Within the first week of the long day with moisture stress treatment, neoformed-leaf initiation ended and bud-scale initiation began. Bud-scale initiation ended by week 3 or 4. Then slow leaf initiation began and continued until week 6. Rate of leaf initiation was rapid during weeks 8–10 and decreased slightly during weeks 10–13. By week 13, apical height had decreased markedly, indicating an imminent end to leaf initiation. Crown cells became apparent within the pith during weeks 5–13; cell walls thickened between weeks 10 and 13. Key words: bud development, dormancy induction, short days, moisture stress, Douglas-fir, seedlings.

Bud development in coastal Douglas-fir seedlings under controlled-environment conditions

Bud development under controlled-environment conditions in coastal Douglas-fir (Pseudotsugamenziesii var. menziesii (Mirb.) Franco) seedlings was investigated. In eight dormancy induction treatments, type of short, day, temperature, and moisture varied. Photoperiod was decreased to 8 h either abruptly (abrupt short day) or gradually (gradual short day). Temperature was either constant at a high temperature or gradually decreased to a low temperature. Moisture was controlled either to result in no moisture stress or to cause moisture stress. Once a 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 leaf) separated by a transitional phase. The change from neoformed-leaf to bud-scale initiation was faster, fewer bud scales were initiated, and the development of the bud-scale complex was faster under abrupt short day than under gradual short day. The transitional phase was shorter and hence leaf initiation began earlier under abrupt short day than under gradual short day and under no moisture stress than under moisture stress. More leaf primordia were initiated under abrupt short day than under gradual short day and under no moisture stress than under moisture stress. The bud-scale receptacle was concave under abrupt short day and convex under gradual short day. Crown height was greater under abrupt short day than under gradual short day.

Influence of dormancy induction treatments on western hemlock seedlings. I. Seedling development and stock quality assessment

Western hemlock (Tsugaheterophylla (Raf.) Sarg.) seedlings were grown in a greenhouse and subjected to four dormancy induction treatments (DIT) (i.e., long-day dry, long-day wet, short-day dry, and short-day wet) during midsummer. In the late summer and fall, seedling development was monitored and it was found that (1) short-day DIT caused a rapid cessation of shoot growth; (2) short-day DIT caused rapid fall development of needle primordia, while long-day DIT took until midwinter to produce the same number of needle primordia; and (3) short-day DIT seedlings had lower saturated and turgor loss point osmotic potentials and greater maximum modulus of elasticity in October than long-day DIT. Seedlings were tested with a comprehensive stock quality assessment procedure just before late winter field planting. These tests showed the following: (1) morphological parameters: short-day DIT reduced shoot to root ratios; (2) pressure–volume analysis: short-day wet seedlings had the lowest osmotic potentials at saturation and turgor loss point; (3) soluble sugar analysis: greater levels of total soluble sugars were found in non water stressed DIT compared with water stressed DIT seedlings; (4) seedling water movement: short-day DIT seedlings had the lowest resistance to water movement at low root temperature (5 °C); (5) low root temperature response: short-day compared with long-day DIT seedlings had greater photosynthesis and stomatal conductance at low root temperatures; (6) root growth capacity: seedlings from all DIT were capable of growing roots at optimum root temperature (22 °C), but short-day compared with long-day DIT had greater root growth at low root temperatures; (7) drought stress response: short-day wet seedlings had the highest photosynthesis and stomatal conductance levels as predawn shoot water potentials decreased; and (8) frost hardiness: short-day wet seedlings had the least needle damage when tested at temperatures of −15 and −18 °C.

Influence of dormancy induction treatments on western hemlock seedlings. II. Physiological and morphological response during the first growing season on a reforestation site

Western hemlock (Tsugaheterophylla (Raf.) Sarg.) seedlings from four dormancy induction treatments (DIT) (i.e., long-day dry, long-day wet, short-day dry, short-day wet) were planted on a coastal reforestation site in British Columbia and monitored for physiological response and morphological development over the first growing season. Seedlings in all DIT showed a similar net photosynthetic, needle conductance, and shoot water potential response to seasonal low temperature, non droughty, and late summer drought conditions. Pressure–volume analysis at the beginning of the growing season (late February) showed short-day wet seedlings to have lower saturated and turgor loss point osmotic potentials than other DIT, while at the end of the growing season (October) there was no osmotic potential difference between DIT. At the end of the growing season, short-day wet seedlings had a much lower maximum modulus of elasticity than other DIT, indicating their shoots were still elongating. Morphological assessment 1 month after field planting showed short-day DIT seedlings had less needle damage and greater root development in response to continuous low temperature exposure. Four months after planting, long-day wet seedlings had the greatest shoot (i.e., height, root collar diameter) and root development in response to mild temperatures and high soil moisture conditions. Eight months after planting, survival was between 95 and 97% for all DIT. Long-day DIT seedlings had the greatest height and all DIT had similar root collar diameter and root development. Short-day DIT seedlings had the best shoot/soil roots ratio. Short-day wet seedlings had the least number of stem units per centimetre of new shoot development throughout the growing season. Results are discussed in reference to stock quality assessment presented in the first paper of this series.

Stock quality assessment through an integrated approach

Forest regeneration can be improved by matching seedling stock with reforestation site environmental conditions. To achieve this improvement, one must characterize seedling performance potential with anticipated field site conditions. A theoretical performance potential index (PPI) has been developed to forecast seedling field performance during the first growing season on a reforestation site. PPI includes material and performance attribute tests that characterize seedling performance potential under optimum and limiting environmental conditions. Test results are standardized and then integrated resulting in a comprehensive assessment procedure. The PPI concept is demonstrated using containerized western hemlock (Tsuga heterophylla (Raf.) Sarg.) seedlings subjected to a series of dormancy induction treatments and the results are compared with actual seedling performance during the first growing season on a reforestation site. Results indicated that PPI values for western hemlock seedlings treated with various dormancy induction treatments corresponded to field performance. Possible use of PPI in stock selection is discussed.

Effects of photoperiod and moisture availability on shoot growth, seedling morphology, and cuticle and epicuticular wax features of container-grown western hemlock seedlings

The influence of short-day and long-day photoperiods, and moderate drought stress (−1.0 MPa), all applied for 4 weeks beginning in mid-July, 1986, was studied on greenhouse-grown western hemlock (Tsugaheterophylla (Raf.) Sarg.) seedlings cultured in two Styroblock container cavity sizes. Shoot growth, morphology, and cuticle and epicuticular wax features were investigated. Weekly measurements of shoot growth were made from early June until growth cessation in October. Root collar diameter, shoot length, numbers of branches and needles, and needle lengths were recorded after shoot growth cessation in another subsample of trees. Shoot growth rapidly ceased under short days, whereas free growth continued under long days. Moisture stress had no effect on shoot growth phenology but significantly reduced final values for all morphological variables. The trends were similar in seedlings from both container sizes, but values were greater in those from the larger containers. Long days increased the total number of leaves and branches, especially under no moisture stress conditions. Under long days, stem unit and needle lengths were increased in the proximal portion of the shoot, whereas moisture stress alone reduced these values in the distal section of the shoot. Dormancy induction treatments had little effect on needle cuticle and epicuticular wax features, although fusion of wax rodlets in the stomata was less common under moisture stress conditions.