Search Results

You are looking at 11 - 15 of 15 items for

  • Author or Editor: Theo J. Blom x
Clear All Modify Search
Free access

Janni Bjerregaard Lund, Theo J. Blom and Jesper Mazanti Aaslyng

Controlling plant height without the use of plant growth retardants is one of the goals in future production of potted plants. Light quality with a low red to far-red ratio (R:FR) increases plant height. In this trial, the effects of light quality [R:FR ratio of 0.4, 0.7, and 2.4 (R = 600–700 nm, FR = 700–800 nm)] at the end of day were investigated on potted chrysanthemums using growth chambers. After a 9-h photoperiod, the 30-min end-of-day lighting was provided by light-emitting diodes at low irradiance by maintaining either red = 1 μmol·m−2·s−1 (Rcon) or far-red = 1 μmol·m−2·s−1(FRcon). After 3 weeks of end-of-day lighting, plants given the lowest end-of-day ratios (R:FR of 0.4 or 0.7) were taller than control plants (R:FR = 2.4). For low ratios of R:FR (0.4), the actual intensities of R and FR did not affect plant height, whereas for higher ratios of R:FR (0.7 and 2.4), plant height was greater for FRcon than for Rcon. Leaf area of the lateral side shoots was lower for plants treated with an R:FR of 0.4 compared with those of controls. Dry weight, stem diameter, number of internodes, and number of lateral branches were unaffected by the end-of-day ratio.

Free access

William N. MacDonald, M. James Tsujita and Theo J. Blom

Chrysanthemum morifolium Ramat. cv. `Yellow Favor' was grown single stem in 10cm pots on an ebb and flow benching system. A 2×2 factorial design was employed with 2 sources of N (100 NO3 and 50 NO3 :50 NH4 +), delivered at 18 mM, and 2 quantities of N supplied, (200 mg and 400 mg), with 200 mg supplied by wk 3 and 400 mg supplied by wk 5. Plants were harvested at two wk intervals, separated into leaves, stems plus petioles and inflorescence (when developed) and analyzed for total and NO3 - N, with reduced N being estimated as the difference between these two values. Plant tissue (leaves and stems plus petioles) NO3 - levels showed similar trends for the 200 and 400 mg N supply, with a maximum at the 4th to 6th wk. At flowering, (wk 10) significant tissue NO3 - levels were found only in plants supplied 400 mg of N. Plants supplied with 50:50 NH4 +: NO3 - initially had significantly greater reduced N and leaf area than NO3 - supplied plants, although differences diminished towards flowering. During floral development (wk 8 to 10), at which time no additional N was accumulated by the plant, significant amounts of reduced N was remobilized from the stem plus petioles and leaves to the developing inflorescence.

Free access

William N. MacDonald, M. James Tsujita and Theo J. Blom

Excessive supply of fertilizer N can lead to inefficient use of supplied N and consequently affect plant quality. Reduction of supplied fertilizer N can possibly increase plant N usage efficiency and improve quality. Chrysanthemum morifolium Ramat. cv. `Yellow Favor' was grown single stem in 10 cm pots on an ebb and flow benching system. All plants received 18.5 mM NO3 - N, until the mid point of this ten wk crop, at which time the following NO3 - concentrations (mM) were employed: 18.5, 15.5, 12.5, 9.5, clear water and clear water alternating with 18.5 mM NO3 -. Plants were harvested at two wk intervals, cut in half and separated into leaves, stems plus petioles and inflorescence (when developed). Plant tissue from the lower half of the plant was analyzed for total and NO3 - N, with reduced N being estimated as the difference between these two values. All growth parameters measured did not significantly differ, although termination of N fertilization (clear water) and reduction of NO3 - level to 9.5 mM significantly reduced NO3 - levels in the lower leaf and stem plus petioles, with a concomitant increase in reduced N in these tissues, over the 6-10 wk period. Total amounts of N accumulated in plant tissues analyzed did not differ significantly at flowering.

Free access

Lisa J. Skog*, Theo Blom, Wayne Brown, Dennis Murr and George Chu

Ozone treatment has many advantages for control of fungal diseases. There are no residue concerns, no registration is required, and it is non-specific, therefore potentially effective against a broad spectrum of pathogens. However, ozone is known to cause plant damage. There is little information available on either the ozone tolerance of floriculture crops or the levels required to kill plant pathogens under commercial conditions. Nine floriculture crops (begonia, petunia, Impatiens, Kalanchoe, pot roses, pot chrysanthemums, lilies, snapdragons and Alstroemeria) were subjected to increasing levels of ozone. Trials were conducted at 5 and 20 °C (90% to 95% RH) and ozone exposure was for 4 days for either 10 hours per day (simulating night treatment) or for 10 minutes every hour. Damage was assessed immediately after treatment and after an additional 3 days at room temperature in ozone-free air. Trials were terminated for the crop when an unacceptable level of damage was observed. Trials to determine the lethal dose for actively growing pathogens (Alternaria alternata, Alternaria zinniae and Botrytis cinerea) and fungal spores were conducted under identical conditions. Ozone tolerance varied with plant type and ranged between <0.2 and 3ppm. Generally, the crops surveyed were more susceptible to ozone damage at the low temperature. As a group, the bedding plants were the least tolerant. Fungal spores were killed at treatment levels between 0.8 and 2 ppm ozone. The actively growing fungal mycelium was still viable at 3 ppm ozone when the trial had to be terminated due to ozone-induced structural damage in the treatment chambers. Under the trial conditions, only the Kalanchoe would be able to tolerate the high levels of ozone required to kill the fungal spores.

Full access

Wayne Brown, Theo J. Blom, George C.L. Chu, Wei Tang Liu and Lisa Skog

The sensitivity of easter lilies (Lilium longiflorum) to either ethylene or methane (products of incomplete burning in gas-fired unit heaters) was tested during rooting [3 weeks at 18 °C (65 °F)], vernalization [6 weeks at 6 °C (43 °F)] and subsequent greenhouse forcing (15 weeks at 18 °C). Starting at planting, easter lilies were exposed for one of seven consecutive 3-week periods (short-term), or for 0, 3, 6, 9, 12, 15, 18, or 21 weeks starting at planting (long-term) to either ethylene or methane at an average concentration of 2.4 and 2.5 μL·L-1(ppm), respectively. Short- or long-term exposure to ethylene during rooting and vernalization had no effect on the number of buds, leaves, or plant height but increased the number of days to flower. Short-term exposure within 6 weeks after vernalization reduced the number of buds by 1 bud/plant compared to the control (no ethylene exposure). However, extensive bud abortion occurred when plants were exposed to ethylene during the flower development phase. Long-term exposure to ethylene from planting until after the flower initiation period resulted in only two to three buds being initiated, while continued long-term exposure until flowering caused all flower buds to abort. Short-term exposure to methane at any time had no effect on leaf yellowing, bud number, bud abortion, or height and had only a marginal effect on production time. Long-term exposure to methane from planting until the end of vernalization increased both the number of buds, leaves and height without affecting forcing time, leaf yellowing or bud abortion.