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Watercress (Nasturtium officinale R.Br.) plants were grown in growth chambers at 15 °C or 25 °C and either 8- or 12-h photoperiod (PP). The photosynthetic photon flux (PPF) was 265 μmol·m-2s-1 in all chambers, but beginning 1 week before harvest, half of the plants in each chamber were subjected to a higher PPF (435 μmol·m-2·s-1). At harvest, watercress leaves and stems were analyzed for phenethyl isothiocyanate (PEITC) concentration. Without supplemental PPF, watercress grown at 25 °C and 12-h PP produced higher PEITC concentration in leaves and stems than plants grown at 15 °C and 12-h PP, or plants grown at 8-h PP and either temperature. With one week of supplemental PPF before harvest, plants grown at 15 or 25 °C and the 8-h PP produced PEITC concentrations as high as plants exposed to 12-h PP and similar temperatures. However, a week of supplemental PPF did not alter PEITC concentrations in plants grown at the 12-h PP, regardless of temperature. At 25 °C, plants grown under the low PPF and the 12-h PP produced 62% greater dry mass than plants exposed to a week of high PPF and the 8-h PP, but did not differ in PEITC content. Thus, the effect of one week of high PPF on PEITC concentration depended on photoperiod.
Forty-two poinsettia cultivars were grown as a 15-cm single-plant pinched crop at 21/16.5°C (day/night) temperatures during Fall 1995 with standard commercial practices for irrigating, fertilizing, and pest control. On 7 Dec., 156 consumers rated the cultivars for their overall appeal. On 11 Dec., color coordinate (CIELAB) readings for bracts and leaves were taken with a Minolta 200b colorimeter. The colorimeter was set to illuminate C and has a 8-mm aperture. Bracts and leaves were placed on a white tile background for colorimetric readings. In 1996, a similar evaluation was conducted with 55 poinsettia cultivars. Using the L-value of leaves as a criterion, cultivars were separated into medium green-leafed and dark green-leafed groupings. For bracts among the red types, hue angle values were used to separate cultivars into cool red types (hue angle ≈20–22°) and warm red types (hue angle ≈24–25°). Based on the 1995 study, cultivars within the cool red bracts and dark green foliage group—those that were darker, duller red (lower L and chroma)—were less attractive (lower consumer ratings) than lighter, more-vivid red cultivars. For cultivars within the cool red bracts and medium green foliage group, consumers preferred the darker duller red cultivars. Perhaps dark foliage gives a more pleasing contrast with the more vivid cool reds than does the medium green foliage. In general, consumers rated red cultivars hire than non-red cultivars.
Poinsettia (Euphorbia pulcherrima Willd. ex. Klotzch) cultivars vary widely in susceptibility to bract necrosis, a disorder that has been associated with localized calcium deficiency. When `Supjibi Red' (SR) poinsettia shoots were grafted on `SR' stocks, a higher incidence of bract necrosis was observed (26.4% of bracts) 28 days after initial anthesis than on corresponding `SR' shoots grafted on `Annette Hegg Dark Red' (AH) stocks (13.8% of bracts). `AH' shoots developed few bract necrosis symptoms, regardless of rootstock. Calcium (Ca) concentrations were higher in whole bracts of `AH' than of `SR', but were unaffected by rootstock. In a second study, `SR' shoots were grafted on a double rootstock of one `AH' and one 'SR' to determine if removing either rootstock, at the start of flower initiation or at anthesis, affected bract necrosis. At 28 days after initial anthesis, `SR' scions on only `AH' roots from the beginning of flower initiation, or on `AH' roots from time of initial anthesis, had less bract necrosis (12.3% and 14.9%, respectively), than `SR' scions grafted on only `SR' roots from the onset of the study (24.2%). At harvest (36 days after anthesis), Ca concentrations in bract margin tissues were highest on `SR' shoots grafted to `SR' roots throughout the study [0.17% of dry mass (DM)], and lowest on shoots grafted to only `AH' from the time of flower initiation (0.15% of DM) or from time of initial anthesis (0.14% of DM). There was no significant correlation between Ca concentrations in bract margin tissue and bract necrosis. A single spray of benzyladenine to bracts, after bract necrosis symptoms first began to appear (at initial anthesis), totally arrested the further development of bract necrosis for up to 34 days. Similar treatment with daminozide increased the incidence of bract necrosis. This evidence suggests a new concept of bract necrosis etiology that includes a role for endogenous hormones. Chemical names used: N,N, dimethylaminosuccinamic acid (daminozide), N 6-benzylaminopurine (benzyladenine).
`Angelika White' poinsettias (Euphoria pulcherrima Willd.ex. Klotzch) were grown hydroponically with modified Hoagland's solution concentrations of 2 or 8 mS·cm-1. The 8-mS·cm–1 rate was imposed by proportionate increases in Ca(NO3)2, KNO3, and MgSO4. Water use, whole plant fresh mass, and pan evaporation were measured gravimetrically twice weekly over a 2-week period beginning 12 Oct. 1995. Poinsettia leaf water loss (g H2O/dm2 of estimated leaf area per day) was 0.30 and 0.22 times pan evaporation (g H2O/dm2 of pan area per day) for the plants in the 2 and 8 mS·cm–1 solutions, respectively (a 25% reduction in water loss for plants in the 8 mS·cm–1 solution), as compared to plants in the 2 mS·cm–1 solution. At initial anthesis, a reciprocal transfer of plants between the 2 and 8 mS·cm–1 solutions was used to investigate the time when plants were sensitive to high soluble salts for bract necrosis. Other plants were maintained throughout the experiment in the 2 and 8 mS·cm–1 solutions. On 15 Jan. 1996, plants were harvested and total lamina surface of leaves and bracts, number of necrotic bracts, and dry mass of leaves, bracts, stems, and roots were recorded. The results indicated that exposure to high soluble salts (8 mS·cm–1) prior to anthesis significantly increased the percent incidence of bract necrosis and decreased root growth. The smaller the root dry mass as a percent of total plant dry mass the greater the incidence of bract necrosis (Y = 0.0972X2 – 3.78X + 38.7, r 2 = 0.69).
Watercress plants were grown in growth chambers at 15°C or 25°C and either an 8- or 12-hour photoperiod (PP). The photosynthetic photon flux (PPF) was 265 μmol·m–2·s–1 in all chambers, but beginning 1 week before harvest, half of the plants in each chamber were subjected to a higher PPF (434 μmol·m–2·s–1). At harvest, watercress leaves and stems were analyzed for phenethyl isothiocyanate (PEITC) content. Watercress grown at 25°C, the 12-hour PP, and 1 week of high PPF produced the highest PEITC concentration in leaves and stems, and plants grown at 15°C, the 8-hour PP, and the low PPF until harvest produced the lowest PEITC concentration. Plants grown at the 8-hour PP, then exposed to 1 week of high PPF, produced 57.3% and 45.9% greater PEITC at 25 and 15°C, respectively, then plants exposed to the low PPF until harvest. However, plants grown at the 12-hour PP and subjected to 1 week of high PPF produced PEITC levels similar to plants grown under the low PPF at 25 and 15°C. At 25°C, plants grown under the low PPF and the 12-hour PP produced 62% greater dry mass than plants exposed to 1 week of high PPF and the 8-hour PP, but did not differ in PEITC content. Thus, the effect of 1 week of high PPF on PEITC concentration depended on photoperiod.
Easter lilies, Lilium longiflorum Thumb. cv Nellie White, were grown in a commercial pine bark-based medium (25% by vol.), amended with 0.5 g Acrylamide Acrylate Gel (AAG) per 1.6 liter pot. Lilies were grown in media drenched with ancymidol, at 0, 0.25, 0.375 or 0.5mg a.i.pot-1 following shoot emergence, or grown in media containing ancymidol impregnated AAG at 0, 0.25, 0.375 or 0.5mg a.i.pot-1. AAG applied ancymidol treatments resulted in a significant linear decrease in both lily stem and internode length as the rate of ancymidol increased. Drench applied ancymidol had no affect on stem or internode length. Stem and internode lengths of drench treated lilies were not significantly shorter than lilies not exposed to ancymidol. Bud length, leaf and bud number, and days to anthesis were not affected (P≤0.05) by any treatment. Ancymidol activity in the top, middle and bottom strata of medium filled containers, and in the leachate from these containers, was measured using a lettuce hypocotyl length bioassay. Ancymidol activity was uniformly distributed throughout the bark medium when applied in AAG. With this treatment, 10-15% of the ancymidol activity was detected in the leachate. When ancymidol was applied as a drench, over 95% of the activity was detected in the top two strata, with 70% in the upper most stratum and the rest in the leachate.
The leaves of many plant species exhibit a noticeable color change in response to water stress. A study was conducted to determine if physiological changes associated with imposed water stress could be correlated with quantifiable leaf color changes in Catharanthus roseus. The Minolta Chroma Meter CR-200 was used to measure leaf color changes during water stress in three cultivars of Catharanthus. In addition, soil and plant water content, osmotic pressure, net photosynthetic rate, transpiration rate, and stomatal conductance were determined. Two components of light, chroma and L value, showed a correlation to the water content of the plant tissue. As plant water content decreased, both chroma and L value decreased. Since a change in leaf color (or a component of color) is easily monitored, the Chroma Meter could ultimately be used to detect incipient water stress in greenhouse crops.
In recent years, Catharanthus roseus has become a popular bedding plant, but at present there is little cultural information available for growers. This study examines the effects of four different temperature regimes and two light levels on three cultivars of Catharanthus. Average daily temperature regimes ranged from 15.3°C to 27.3°C; light intensities were 125 μmolm-2s-1 and 250 μmolm-2s-1. Plants were harvested as each successive pair of true leaves reached 1.5 cm in length, from the first true leaf stage until flowering. Measurements included internode length, leaf length, leaf area, dry weight of stem and leaves, and number and length of shoots. The plants grown at the lowest temperature regime took four times as long to flower as those grown at the highest temperature regime. Plants grown at the coolest temperature also exhibited chlorosis, stunting, and unusual flower formation. Information obtained from this study should assist growers in determining their planting schedule and the optimum greenhouse temperature for desired plant habit.
As water resources become limited, agricultural producers must resort to alternative sources for irrigation, including municipal reclaimed water which may contain impurities such as salts that can adversely impact irrigation management practices and crop yield. To test the effects of salinity on plant growth and nutrient composition under greenhouse conditions, zinnia (Zinnia elegans) was produced under two different subirrigation management regimes and exposed to various concentrations of NaCl to simulate the crop production challenges associated with poor water quality. Plants received either short- or long-cycle subirrigation to achieve differing levels of potting medium saturation at each irrigation event. Plants under these two irrigation management regimes were challenged with NaCl at concentrations up to 1.5 g·L−1 or 3 dS·m−1 . Zinnia plants accumulated more Na in shoot tissues as salinity in the irrigation water increased from 0 to 1.5 g·L−1. The electrical conductivity (EC) in the potting medium also increased over time, and the rate of leaf area expansion decreased with increasing levels of salinity in the irrigation water. Short-cycle irrigation management has been shown to increase fertilizer and water use efficiency (WUE), thereby reducing the costs associated with these resources and also reducing the environmental impacts of agricultural crop production. In our study, the medium under short-cycle subirrigation management had lower gravimetric water content (GWC), both before and after irrigation, than the medium under long-cycle subirrigation, but the drier medium conditions did not increase susceptibility to salt injury. Furthermore, plants grown under short-cycle irrigation management for 4 to 6 weeks accumulated less Na in shoot tissue than plants grown under long-cycle irrigation management. Sodium accumulation in the shoot tissues was a product of both the amount of sodium in the irrigation solution and the amount of water used by the plant over time. Therefore, short-cycle subirrigation can be used as an effective water management technique even when raw water quality is poor as represented by elevated salinity. Our research indicates that zinnia can be irrigated with saline water up to 0.5 g·L−1 NaCl (an EC of 1 dS·m−1) in a 5-week production cycle without adverse effects on growth.
Abstract
Poinsettias (Euphorbia pulcherrima Willd. cv. Annette Hegg Brilliant Diamond) were grown in separate greenhouses, one in which the night air temperature was maintained at 16.7°C and another where the air temperature was allowed to fall to 11.5°. The cool-air-treated plants were subjected to root-zone temperatures of 17°, 23°, 26°, and 29°. In general, the deleterious effects of cool air temperatures could be reversed by root-zone warming at 23°.