Yong Ha Rhie

Flowering of cyclamen is accelerated by an increase in temperature, photoperiod, and daily light integral

Summary Cyclamen (Cyclamen persicum Mill.) crop production times can be reduced by increasing the greenhouse temperature, but alternative methods to accelerate crop development are desirable when energy costs for heating are high. The effects of photoperiod and increasing daily light integral (DLI) on cyclamen remain unclear. We performed experiments to examine the effect of DLI using two temperatures (16°C or 20°C) and three photoperiods (8, 12, or 16 h) delivering DLI values of 4.9, 7.3, or 9.8 mol m–2 d–1, respectively, and the effect of night interruption (NI) lighting from incandescent lamps (IL), on the flowering of cyclamen ‘Metis Purple Flame’. Plants grown at 20°C reached the visible flower bud (VB) stage earlier than plants grown at 16°C under all photoperiods. NI hastened flower bud initiation by 22 – 29 d compared with an 8-h photoperiod at both temperatures. Plants grown under the 8-h photoperiod with an NI treatment (DLI = 4.9 mol m–2 d–1) flowered at a similar time as plants grown under the 12-h photoperiod (DLI = 7.3 mol m–2 d–1). In addition, plants grown at 16°C with an NI reached the VB stage in a similar time to plants grown at 20°C with an 8-h photoperiod. Therefore, the effects of increasing the DLI, providing NI lighting, or increasing the temperature can be compared, so that growers can determine which strategies can reduce the greenhouse production time of cyclamen most cost-effectively.

Chilling requirement for breaking dormancy and flowering in Paeonia lactiflora ‘Taebaek’ and ‘Mulsurae’

Dormant rootstocks of Paeonia lactiflora ‘Taebaek’ and ‘Mulsurae’ (native Korean cultivars) were stored at three chilling temperatures (constant 0, 5, or 10°C) for different durations (0, 3, 6, 9, or 12 weeks) to determine the chilling requirements for dormancy breaking and flowering. For both cultivars, percent sprouting, numbers of shoots and flowers, and height during flowering increased as the plants were exposed to lower chilling temperatures or longer chilling durations, whereas the time required for sprouting gradually decreased as the duration of the chilling treatment increased. However, there were no significant differences in these parameters between the two cultivars when they were chilled for 9 weeks or more. A chilling treatment at 0°C for 6 weeks [1,008 hours chill unit (CU)] produced more number of shoots and flowers and required fewer days to achieve sprouting and flowering than at 5°C for 6 weeks (706 hours CU). Temperatures of 5°C and 10°C afforded only 70% and 40%, respectively, when compared to a cumulative chill unit at 0°C. ‘Taebaek’ required more chilling to sprout consistently and achieve its potential shoot numbers than ‘Mulsurae’. Chilling for 6 weeks at 0 and 9 weeks at 5°C (1,058 hours CU) were necessary to break dormancy and to induce flowering in P. lactiflora ‘Taebaek’ and ‘Mulsurae’, respectively.

Dormancy Release and Flowering of Paeonia lactiflora 'Taebaek' by Natural Cumulative Chilling and GA3 Treatment

Dormancy breaking and flowering of Paeonia lactiflora ‘Taebaek’ were controlled by natural cumulative chilling and GA3 treatments according to the transfer date in the central region of Suwon, Korea. Shoot emergence and flowering did not occur throughout the experimental period when dormant rootstocks were transferred to a glasshouse between September 10 and October 29, in which the natural cumulative chill (NCU) unit was nearly 0 h. The number of days from the transfer date to sprouting and flowering was shortened as the transfer date was delayed. All the plants flowered normally with shoot growth when they were transferred after December 31 (1,222 h NCU). All dormant buds that were treated with GA3 sprouted, regardless of transfer date, but failed to flower due to shoot blasting and flower bud abortion when they were transferred between September 10 (0 h NCU) and November 12 (185 h NCU). Shoot blasting was 38% when they were transferred on November 26 (429 h NCU). When GA3 was applied to the plants after December 17 (876 h NCU), they flowered without blasting. Plant height and stem diameter were not affected by GA3 treatment. GA3 treatment decreased the number of days to sprouting and flowering, and increased the number of flowers, irrespective of insufficient chilling accumulation, as compared to 1,222 h NCU on December 31. According to the above results, at least 1,222 h NCU could be recommended as a practical forcing method for dormancy release, subsequent growth, and normal flowering of dormant P. lactiflora ‘Taebaek’ in a temperate climate region. The GA3 treatment played an important role in breaking dormancy and significantly increased the percentage of sprouting, accelerated the days to sprouting and promoted the flowering of P. lactiflora ‘Taebaek’ when the plants had undergone insufficient chilling accumulation.

Chilling requirement for dormancy release of variegated Solomon’s seal

Dormancy release of variegated Solomon’s seal (Polygonatum odoratum Druce var. pluriflorum Ohwi for. variegatum Y.N.Lee) was studied by varying the transferring date from the field to greenhouse and by cold storage in order to identify their precise chilling requirement. Bud emergence and flowering did not occur throughout the experiment when dormant rhizomes were transferred until a calendar date November 22, 2009, in which natural cumulative chill unit (NCU) was 75 h. Days to sprouting, flowering, and flower abscission were shortened with delayed transferring dates. Percent sprouting and flowering showed an increasing tendency since rhizomes were transferred on December 7 (= 241 h NCU), but emergence date was not uniform. However, uniform percent sprouting was maintained since rhizomes were transferred on December 22 (= 492 h NCU). No or 1 week of cold storage at 0 or 5°C did not induce sprouting, which meant bud dormancy was not released when rhizomes were stored ≤ 1 week. When they were stored for more 2 weeks at 0 or 5°C, percent sprouting was increased to ≥ 91% in the heated greenhouse. Cumulative chill unit (CCU) was 336 h at 0°C and 225 h at 5°C. However, bud emergence date after 2 weeks of cold storage was not uniform at both storage temperatures, whereas bud emergence after 4 weeks of cold storage at 0°C was more uniform than that at 5°C. Therefore, at least 492 h NCU, 4 weeks of cold storage at 0°C (= 672 h CCU), or 6 weeks at 5°C (= 675 h CCU) is recommended for forcing and normal growth afterward of variegated Solomon’s seal.

Non-deep simple morphophysiological dormancy in seeds of Thalictrum rochebrunianum, an endemic perennial herb in the Korean Peninsula

The aims of this study were to determine the requirements for dormancy break and germination and to characterize the type of seed dormancy of T. rochebrunianum. Ripe seeds (achenes) were collected in late Sept. To determine the temperature requirements for embryo growth and germination in the field, the seeds were sown in field soil. Every 1 or 2 weeks, the seeds were exhumed, and the phenology of embryo growth, germination and seedling emergence were investigated. In the laboratory, effects of temperature and GA3 treatment on embryo growth and germination were also investigated to characterize the type of seed dormancy. Seeds had underdeveloped embryos, which were about 20% of the size of those in fully matured seeds. In natural conditions, embryo growth and germination occurred in early and late March next year, respectively, and embryos in the seeds of this species had to grow to a critical length before germination was possible. Thus, the seeds had morphological dormancy (MD). When tested at the time of dispersal, few seeds germinated after 4 weeks of incubation at 25/15°C. Therefore, the seed dormancy type for T. rochebrunianum seemed to be morphophysiological. Embryos in the seeds grew rapidly at warm temperature conditions following cold stratification at low temperatures. After 4–12 weeks of cold stratification at 1°C or 5°C, the seeds germinated rapidly during an incubation at 25/15°C. Cold stratification requirements could be substituted by GA3 treatment in seeds of T. rochebrunianum. After 1000 mg·L-1 GA3 treatment, high percentages (≥ 80%) of the seeds germinated after 4 weeks of incubation at 15/6, 20/10, and 25/15°C. Consequently, seeds of T. rochebrunianum could be characterized as expressing non-deep simple morphophysiological dormancy (MPD). The cold stratification requirements for dormancy break enabled the seeds to produce seedlings at the beginning of the growing season in natural conditions.

Breaking Bud Dormancy in Erythronium japonicum Decne. (Liliaceae) by Natural and Artificial Chilling

This study was conducted to investigate flower bud differentiation and to determine the chilling requirements for bud dormancy breaking and sprouting in Erythronium japonicum Decne. (Liliaceae). Dormant bulbs grown in an open field were randomly selected from June 2012 to December 2013 for observation of flower bud differentiation and development. The 3–4 year-old bulbs and > 10 year-old bulbs were used for vegetative bud development and flower bud development, respectively. For natural chilling treatments, the plants were transferred from an experimental field to a growth module every month from September to February. Artificial chilling treatments were applied at 5°C for 0, 2, 4, 8, and 12 weeks in October and November. The cumulative chill unit (CCU) of low temperatures below 5°C was calculated. Flower bud initiation and differentiation in E. japonicum were observed in May, and from June to July, respectively, followed by flower bud elongation in August. Sprouting and bud break did not occur throughout the experiment when dormant bulbs were transferred from September (0 CCU) to November (450 CCU). However, all plants sprouted when the dormant bulbs were transferred after January (1,794 CCU). Prolonged cold storage also promoted sprouting of dormant E. japonicum. No cold storage or 4 weeks (672 CCU) of cold storage at 5°C in October did not induce sprouting and bud break. However, when the dormant bulbs were stored at 5°C for 12 weeks (2,061 CCU) in October, percent sprouting increased to 72.7%. Chilling treatment for 8 weeks (1,483 CCU) or 12 weeks (2,155 CCU) at 5°C in November resulted in 72.7 and 100% sprouting, respectively. In conclusion, at least 1,483–1,794 CCU may be recommended for dormancy breaking in the forcing culture of E. japonicum.

Pre-chilling Promotes Flowering in Paeonia lactiflora 'Taebaek' without Flower Bud Abortion

This study was conducted to prevent flower bud abortion in forcing culture of herbaceous peony. When dormant rootstocks of Paeonia lactiflora ‘Taebaek’ were subjected to dormancy-breaking treatment (0°C for 6 weeks) in November, this could hasten flowering in early spring. However plants chilled in August, September, or October produced abnormal flowers or resulted in flower bud abortion. To prevent flower bud abortion, we placed the dormant rootstocks at five pre-chilling treatments for 2 weeks in mid-September and October. The treatment conditions were 0°C for 2 weeks (C0, control), natural chilling in an open field for 2 weeks (NT), pre-chilling at 15°C for 2 weeks (P15), 15°C for 1 week → 10°C for 1 week (P15 → 10), and pre-chilling at 10°C for 2 weeks (P10). After these pre-chilling treatments, all of the plants were placed under a cold regime of 0°C for 6 weeks in order to break dormancy. In the C0 and NT treatments, a great numbers of flower buds were aborted from their stems. On the other hand, the P15 → 10 and P10 treatments increased to 74.7 and 81.0% for flowering, respectively. Pre-cooling treatment accelerated the growth of flower buds compared to the C0 or NT treatments. To promote blooming in the autumn season, rootstocks were also placed into three treatments (C0, NT, and P10) in early July. While the C0 and NT treatment were unable to produce flowering at all, the treatment P10 induced more than 80% flowering of plants. From these results, pre-chilling at treatment 10°C for 2 weeks was recommended as the optimum treatment to promote flowering without flower bud abortion in forcing culture for winter or autumn flowering.