In the commercial development of an innovative process for the production of pathogen-indexed Easter lilies (Lilium longiflorum Thunb.) in less than a year, it became desirable to quantify the cooling period so that the time of flower induction/initiation could be determined. Based upon studies of forcing flowering plants from bulbs, I hypothesized that cooling could be quantified using the cool temperature unit (CTU), defined as 1 °C below 21 °C for 1 hour, and the warm temperature unit (WTU), defined as 1 °C above 21 °C for 1 hour. The purpose of these studies was to determine if the hypothesis was valid. With 'Nellie White' Easter lily, it was determined that cooling could be quantified as hypothesized. The minimum threshold number of CTU that would induce flowering in at least one plant of the test population after exposure to long days was between 1200 and 2400, whereas the threshold number of CTU that would induce flowering in 100% of the population was 3600. The optimum threshold, i.e., the number of CTU that would result in the best market quality, was estimated to be 4800. The studies demonstrate that market quality, pathogen-indexed flowering potted Easter lilies growing continuously from bulblets can be produced in about 1 year, and that the cooling required to sensitize the plants to long days, which is central to the success of the fast production process, is quantifiable.
Catherine M. Whitman, Royal D. Heins, Arthur C. Cameron and William H. Carlson
The influence of cold treatments on flowering in Campanula carpatica Jacq. `Blue Clips' was determined. Plants with 10 to 12 nodes (P1) and 12 to 16 nodes (P2), in 128-cell (10-mL cell volume) and 50-cell (85-mL cell volume) trays, respectively, were stored at 5 °C for 0, 2, 4, 6, 8, 10, 12, or 14 weeks under a 9-hour photoperiod. They then were transplanted and forced in a 20 °C greenhouse under a 9-hour photoperiod with a 4-hour night interruption (NI) (2200 to 0200 hr). Time to visible bud and to flowering in P1 decreased slightly as the duration of cold treatment increased. Flowering was hastened by ≈10 days after 14 weeks at 5 °C. Cold treatments had no significant effect on time to visible bud or flower in P2. The number of flower buds on P1 did not change significantly in response to cold treatments, while flower bud count on P2 increased by up to 60% as duration of cold treatments increased. Final height at flowering of both ages decreased 10% to 20% with increasing duration of cold exposure. To determine the relationship between forcing temperature and time to flower, three plant sizes were forced under a 9-hour photoperiod with a 4-hour NI (2200 to 0200 hr) at 15, 18, 21, 24, or 27 °C. Plants flowered more quickly at higher temperatures, but the number and diameter of flowers were reduced. Days to visible bud and flowering were converted to rates, and base temperature (Tb) and thermal time to flowering (degree-days) were calculated. Average Tb for forcing to visible bud stage was 2.1 °C; for forcing to flower, 0.0 °C. Calculated degree-days to visible bud were 455; to flower, 909.
John M. Dole and Harold F. Wilkins
Easter lily (Lilium longiflorum Thunb. `Nellie White') bulbs were exposed to 1, 2, 3, 4, 5, or 6 weeks of cold before shoot emergence; 0, 1, 2, 3, 4, 5, or 6 weeks of long days (LD) upon shoot emergence; or a combination of cold followed by LD: 1/5 (weeks cold/weeks LD), 2/4,3/3,4/2, or 5/1. Experiments were repeated for three consecutive years. LD did not substitute equally for cold; at least 3 weeks of cold were required before LD treatments resulted in anthesis. Depending on the year, 100% of the plants flowered when treated with 3 to 6 weeks of cold alone or in combination with LD. Days to first flower anthesis from planting increased with decreasing weeks of cold in years 1 and 3, but was similar for all treatments in year 2. Decreasing weeks of cold in combination with LD, however, decreased days to anthesis in years 1 and 2, but had no effect in year 3. Regardless of LD, days from emergence to visible bud increased with decreasing weeks of cold in all years, and days to emergence from placement in the greenhouse increased with decreasing cold in years 1 and 3, but not in year 2. Increasing weeks of cold, regardless of LD, decreased leaf count, but had no effect on plant height. Flower count was unaffected by cold when combined with LD, but was significantly reduced by increasing weeks of cold.
Juan C. Díaz-Pérez, Albert C. Purvis and J. Thad Paulk
Bolting causes significant economic losses in sweet onion (Allium cepa L.) production. Although temperature and photoperiod are considered to be the main factors that initiate bolting in onions, preliminary results suggested that low N fertilization rates increased bolting. The objective of our study was to determine the relationships of bolting, yield and bulb decay with N fertilization rates. The N fertilization rates applied ranged from the infraoptimal to the supraoptimal (from 102 to 302 kg·ha-1 N). Shoot and bulb N content increased with increasing N rates, but there were no differences in the respective shoot and bulb N contents among cultivars. Bolting incidence declined steadily with increasing N fertilization rates up to 197 kg·ha-1 N. Bolting incidence was among the highest in the cultivar Pegasus. The percent of decayed bulbs also increased at a steady rate with the rate of N applied. Total (14.7 t·ha-1) and marketable (0.8 t·ha-1) yields at the lowest N rate (102 kg·ha-1 N) were lower (P ≤ 0.01) than those at higher N rates. Rates of N ≥145 kg·ha-1 had no significant effect on either total (mean = 33.6 t·ha-1) or marketable (mean = 21.6 t·ha-1) yields. Losses in marketable yield were primarily a combination of bolting and bulb decay and were minimized at 162 kg·ha-1 N. Yield losses at low N rates were mostly due to bolting while yield losses at high N rates were mostly due to decay. Thus, excess applications of N fertilizer should be avoided since they have little effect on yields or bolting but they increase bulb decay.
Sylvie Jenni, Isabelle Gamache, John Christopher Côté and Katrine A. Stewart
Growers of early stalk celery (Apium graveolens var. dulce) often experience financial losses due to bolting (the premature and rapid elongation of the main celery stem) in temperate regions. A method was developed to provide early warning of bolting in field-grown celery, on the basis of two criteria, one visual and one microscopic, for inflorescence development. Bolting could be detected 40 days after transplanting using the visual criterion, and as early as 30 days after transplanting using the microscopic criterion. Early detection of bolting using the visual and microscopic criteria provided celery growers with periods of, respectively, 25 days and up to 35 days to consider harvesting earlier, before the length of the celery stems exceeded commercial standards. This method could be effective in minimizing financial losses due to bolting when coupled with agro-economic studies.
M. Peggy Damann and Robert E. Lyons
To examine the effects of chilling and a limited inductive photoperiod (LIP) on flowering of Chrysanthemum superbum Bergmans ex J. Ingram `G. Marconi' and `Snow Lady', Coreopsis grandiflora Hogg `Sunray', and Coreopsis lanceolata L. `Early Sunrise', seeds were sown and plants were maintained in the greenhouse in short days (SDs) for 7 weeks, followed by 4 months of natural outdoor chilling for all plants except 10 of each cultivar, which remained in the greenhouse under SDs for the duration of the experiment. Upon return to greenhouse conditions, 10 plants of each cultivar were placed in SDs, all other chilled plants were placed in long-days (LDs) and subsequently transferred to SDs after receiving 6, 8, 10, 12, 14, 16, 18, 20, or 22 LD cycles. Ten chilled plants of each cultivar remained in LDs for the duration of the experiment. Continuous SDs without chilling resulted in 70%, 40%, 20%, and 10% flowering in `Snow Lady', `Early Sunrise', `Sunray,' and `G. Marconi', respectively. Chilling, followed by a return to continuous SDs, improved flowering in all cultivars compared to SDs without chilling. The number of LD cycles required for 100% flowering varied with cultivar. Ninety percent of the chilled `Early Sunrise' plants flowered with no LD cycles, and 100% flowering was produced by as few as six LD cycles. In `Snow Lady', 100% flowering occurred in chilled plants with no LD cycles and those receiving at least 10 LD cycles. With only six or eight LD cycles, 90% and 80% of these plants, respectively, still flowered. The percentage of `G. Marconi' and `Sunray' plants flowering ranged from 40% to 100% in the chilled treatments, with a general trend for more flowering with an increase in the number of LD inductive cycles. Continuous LDs following chilling resulted in as high or higher percent flowering than any other treatments (100% for `G. Marconi' and 90% for `Sunray'). The effects of LIP were evident in both Coreopsis cultivars but in neither Chrysanthemum superbum cultivar. There was a linear relationship between the number of LDs received and stem length at first flower in `Sunray' and `Early Sunrise'. In both cultivars, a reduction in stem elongation of about 10 cm occurred when plants received only 6 LDs compared to 22 LDs. The number of days from the start of LDs to first flower increased linearly as the number of LD cycles before the transfer back to SDs increased.
R.T. Taylor and E.A. Borchers
`Squire' Scotch kale (Brassica oleracea L.) (n = 9) and `Premier' smooth-leaved kale (B. napus L.) (n = 19) were planted in a field study to compare the onset and rate of flower stalk elongation after overwintering. Flower stalk elongation began 28 days later in `Premier' than in `Squire`; `Premier' plants remained marketable 24 days longer. In spite of the delay in the onset of stalk elongation, siliques of `Premier' were only 3 days later maturing.
Lisa W. Alexander, Anthony L. Witcher and Fulya Baysal-Gurel
narrow, strap-like flower petals and capsulate fruit that co-occurs with flower buds and flowers. North American species include vernal (or ozark) witchhazel, which is found in the Ozark Mountains of Oklahoma, Missouri, and Arkansas, and in Texas; common
Douglas C. Sanders and Jennifer D. Cure
The efficacy of undercutting as a technique to control bolting of two short-day onion cultivars was studied in controlled-environment chambers. `Buffalo' and `Granex 33' onions were grown to the third, fifth, and seventh visible leaf stages in a 10-hour photoperiod at 22/18 °C (day/night) and then exposed to 30, 40, 50, 60, or 70 days of vernalizing temperatures (10/10 °C). Half of the plants were undercut at the initiation of the vernalizing treatment. After vernalizing treatments, plants were returned to 14-hour photoperiods at 22/18 °C. `Buffalo', which is resistant to bolting, did not flower significantly under any of these conditions. The flowering response of `Granex 33' increased with leaf number at vernalization and as the duration of vernalization increased. Undercutting `Granex 33' increased the days of vernalization required for flowering and reduced the proportion of flowering relative to controls. Overall dry-matter accumulation was unaffected by leaf number at vernalization or the duration of vernalization but was reduced ≈30% by undercutting. In both cultivars, fresh mass per bulb decreased with increasing leaf stage of vernalization and number of vernalizing days. Undercutting also decreased fresh mass per bulb, but through its effect on bolting, undercutting increased marketable yield for plants vernalized and undercut at the fifth and seventh leaf stages.
Anusuya Rangarajan and Betsy A. Ingall
Annual production of globe artichokes (Cynara scolymus L.) requires vernalization of the plants, either through cold treatment of transplants or from natural temperature conditions in the spring. Studies were conducted in upstate New York to determine if artificial vernalization treatments could be achieved by earlier planting dates. Initial trials evaluated two cultivars used for annual production in other parts of the country—'Imperial Star' and `Green Globe Improved'. Transplants were set in the field with or without a vernalizing cool treatment, to determine the extent of natural vernalization achieved under New York conditions. `Imperial Star' produced slightly higher marketable yields than `Green Globe Improved' in 2 years of trials. Vernalization treatment increased the number of plants producing buds and the marketable yields, when transplants were set after 15 May. Natural vernalization was achieved and cold treatment prior to transplanting did not improve yields of plants established in early May. At later planting dates, vernalizing transplants increased the number of plants producing apical buds (largest) by about 20%, yet, >57% of non-vernalized plants of each variety produced buds within the season. Average bud sizes did not vary with vernalization treatment. A similar number of days from transplanting to first bud harvest (69 to 75) was noted regardless of planting date and size of transplant.