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Light, moisture, and atmosphere interact to affect the quality of dry-sale lily bulbs
Postharvest Biology and Technology 34 (2004) 93–103
Light, moisture, and atmosphere interact to affect the quality of dry-sale lily bulbs Garry Legnani, Christopher B. Watkins, William B. Miller∗ Department of Horticulture, Cornell University, Ithaca, NY 14853, USA Received 22 May 2003; accepted 15 February 2004
Abstract The interactions of moisture and light with low oxygen (1%) storage of dry sale lily bulbs at 22–25 ◦ C for 4–5 weeks have been studied as part of a continuing evaluation of modified atmospheres (MA) to lengthen shelf life. Conditions that promoted development in storage (light, moisture, and air) were detrimental to final plant quality, resulting in short plants with many aborted flowers and poor foliage development. One percent O2 suppressed pre-plant development compared to storage in air, irrespective of light and moisture. When bulbs were forced under conditions that accelerated growth (high temperatures and light), bulbs stored in darkness, air, and dry (without peat) were comparable in quality (producing normal flowers and having adequate height and foliage development) to bulbs stored with 1% O2 without peat. Exclusion of light is beneficial to bulbs stored in air but is not practical for marketing. The quality of dry-sale bulbs was always inferior to un-treated control bulbs that remained in the cooler during the dry-sale storage period. Untreated bulbs produced taller plants with more flowers and superior foliage development compared to bulbs stored under dry-sale conditions, regardless of the combination of light, moisture, and atmosphere. © 2004 Elsevier B.V. All rights reserved. Keywords: Lilium bulbs; Low oxygen; Moisture; Light; Flowering; Leaf area
1. Introduction In a previous study, we reported an evaluation of the use of modified atmospheres (MA) to extend the shelf life of dry sale lily bulbs (Legnani et al., 2004). The study examined the tolerance of bulbs to storage under low O2 for ca. 30 days at warm temperatures (22–26 ◦ C) with fluorescent light. These ∗ Corresponding author. Tel.: +1 607 255 1799; fax: +1 607 255 9998. E-mail address: [email protected] (W.B. Miller).
temperature and light conditions were chosen to simulate a retail situation in which vernalized bulbs are packaged and displayed in a garden center for springtime sales leading to planting in the garden. The goal is to develop a MA package (MAP) to limit shoot elongation and flower development under dry sale conditions while maintaining bulb viability and the ability to produce a commercially acceptable flowering plant for consumers. The study showed that humidified atmospheres of 1–2% O2 inhibited shoot elongation and flower bud development in three Asiatic hybrid lily cultivars. Overall, plant quality
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was improved by low O2 storage, but varied with cultivar. Commercially, bulbs are often packaged with moist peat moss to minimize physical damage during transport and to prevent desiccation. Since both peat moss moisture content and retail lighting conditions can vary widely, their interactions with O2 concentration are of critical interest to this research. Studies on the effects of controlled atmospheres (CA) (Thornton, 1939; Thornton and Imle, 1941; Stuart et al., 1970; Prince and Cunningham, 1991) and packaging media moisture content (Stuart, 1954; Laiche and Box, 1970; Prince and Cunningham, 1990) have been reported on Easter lily (Lilium longiflorum Thunb.). These studies focused on storage conditions during commercial case handling, vernalization, and their effects on forcing characteristics. Other studies on Easter lily have reported the effects of light intensity on forcing characteristics, dry weight partitioning, and carbohydrate changes (Heins et al., 1982a,b; Wilkins et al., 1986; Miller and Langhans, 1989a,b). To our knowledge no information exists on how these factors influence packaged bulbs in a retail situation. In this paper, we report on the interactions of storage atmosphere, moisture, and light during dry-sale storage of hybrid lily bulbs.
2. Materials and methods 2.1. Experiment 1 2.1.1. Plant material Previously frozen Asiatic hybrid lily bulbs (12/14 cm) (Lilium asiaticum cv. Marseille) were received on 9 September. Bulbs were stored in the dark (1 ◦ C) in their original polyethylene-film-lined containers, with moist peat moss. On 18 October, bulbs were sorted by size with average shoot lengths external to the bulb (±S.E.) of 1.00 ± 0.09 cm. Five bulbs were randomly selected and meristems were examined using a dissecting scope. Meristems were at the pre-floral stage as defined by De Hertogh et al. (1976). 2.1.2. Simulated dry-sale storage Bulbs were placed in cardboard egg-cartons inside 20 l jars. The cartons allowed for an upright orientation of the bulbs. Two egg-cartons, each holding an
experimental unit of 6 bulbs, were placed in each jar. Fresh weights of the experimental units were determined prior to placement in the jars. One egg-carton was enclosed in a polyethylene bag with enough moist peat moss (ca. 75% water content) to cover the bulb scales (peat or no peat treatment). The bags were used to hold the peat moss in place and were not sealed. Jars were either covered with aluminum foil or left uncovered (light or dark treatment) then exposed to humidified atmospheres of air or 1% O2 balanced with nitrogen. Humidified atmospheres were applied using a capillary flow board system at a flow rate of 100 ml/min. Four jars (repetitions) per treatment were arranged in a randomized block three-way factorial design on four shelves within a controlled temperature chamber (21 ◦ C) with fluorescent light. Temperature and relative humidity (RH) inside the jars was monitored using a HOBO Pro temperature and RH recorder (Onsight Computer, Bourne, MA). Temperatures inside the jars averaged 22 ◦ C (foil covered) and 23 ◦ C (uncovered) and RH was ca. 85%. Photosynthetic photon flux density (PPFD) inside uncovered jars at the level of the bulbs was ca. 45 mol m−2 s−1 . The 1% O2 atmosphere was monitored daily using gas chromatography (model 1200 gas partitioner, Fisher Scientific, Springfield, NJ). The percentage of O2 (±S.E.) was 0.97 ± 0.06%. After 35 days, bulbs were removed from the jars and shoot lengths and fresh weights determined. The shoots of two bulbs from each experimental unit were dissected and the meristems examined. The number of flower buds and the size (length in mm) of the largest bud were determined. 2.1.3. Greenhouse forcing The remaining bulbs were planted in 15 cm pots in a 1:2:1 (soil:peat:perlite) mix and placed in a glass greenhouse for forcing. Plants were arranged in a completely randomized design (16 plants per treatment). Bulbs that remained in the cooler (1 ◦ C) without air or low O2 treatments were planted as untreated controls. The greenhouse temperature set point was 20 ◦ C with max/min temperatures reaching 22 ◦ C day and 17 ◦ C night, respectively. Plants were grown with a standard fertilizer regime. Data collected included days to anthesis, total number of flower buds (healthy and aborted), aborted flower buds, and height at flowering (from the rim of the pot to the top of the plant). Additional data included percentage of plants flowering,
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percentage of plants with abnormal flowers, percentage of blind plants (plants not producing flower buds), and percentage of plants not emerging. After all plants in a treatment had flowered, 10 plants were randomly chosen and the total number of nodes (above and below the soil to just below the first pedicle), total number of leaves, total leaf area, and area per individual leaf were determined. 2.2. Experiment 2 2.2.1. Plant material Previously frozen Asiatic hybrid lily bulbs (12/14 cm) cv. Marseille were received on 24 May. Bulbs were stored at 4 ◦ C as previously described. On 4 June, bulbs were sorted by size with average shoot lengths external to the bulb (±S.E.) of 1.80 ±0.11 cm. Meristems were vegetative or at the pre-floral stage. 2.2.2. Simulated dry-sale storage Bulbs were arranged in 20 l jars using the same experimental design as experiment 1. Temperatures inside the jars averaged 24 ◦ C (foil covered) and 25 ◦ C
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(uncovered) and RH was ca. 85%. The percentage of O2 (±S.E.) was 1.10 ± 0.04%. After 24 days, bulbs were removed from the jars and shoot lengths and fresh weights determined and the meristems of two bulbs from each experimental unit were examined as previously described. 2.2.3. Greenhouse forcing The remaining bulbs were planted as previously described. The greenhouse temperature set point was 20 ◦ C day/night with max/min temperatures reaching 27 ◦ C day and 17 ◦ C night, respectively. Plant culture and data collection were as previously described. 2.3. Statistical analyses Analysis of variance (ANOVA) for subsequent interactions was conducted using SAS (Cary, NC). When assumptions for ANOVA could not be met, main effects were analyzed using the Wilcoxon rank sum scores. The least significant difference (L.S.D.) is provided for mean separation. Comparison of dry-sale treatments to untreated controls for percentage of
Table 1 Effects of light, moisture, and atmosphere on pre-transplant growth and development of Asiatic hybrid lily cv. Marseille following a 35 day (experiment 1) or 24 day (experiment 2) storage period Light
Peat
+ − + + + − + + − − − + − − − + LSD0.05 Light (L) Peat (P) Atm (A) L×A L×P P×A L×P×A a b
Atm
1% 1% Air Air 1% 1% Air Air
O2 O2
O2 O2
Shoot length (cm)
Fresh weight loss (−) or gain (+) (%)
Number of flower buds
Experiment 1
Experiment 2
Experiment 1
Experiment 2
Experiment 1
Experiment 2
Experiment 1
Experiment 2
1.6a 3.5 5.6 17.9 2.3 6.4 5.8 20.1 1.78 * *** *** NS NS *** NS
1.8a 5.2 3.3 16.6 2.4 7.3 3.8 22.7 1.58 *** *** *** NS ** *** NS
−13.0a −2.3 −14.5 −4.0 −9.5 +4.5 −11.3 +7.3 2.75 *** *** NS NS ** NS NS
−14.9a +5.2 −13.9 +5.2 −8.5 +5.1 −9.0 +19.6 5.27 ** *** * NS NS * *
0.0b 0.0 3.0 5.8 0.0 0.0 3.8 5.0 1.54 NS * *** NS NS * NS
0.0b 0.0 2.8 5.9 0.0 0.0 2.9 5.8 2.66 NS *** *** NS NS *** NS
0.0b 0.0 2.0 5.5 0.0 0.0 1.3 3.0 1.35 NS ** *** NS NS ** NS
0.0b 0.0 1.8 4.0 0.0 0.0 1.6 4.3 0.82 NS *** *** NS NS *** NS
Means represent the average of four replications with six bulbs per experimental unit. Means represent the average of four replications with two bulbs per experimental unit.
Size of largest flower bud (length in mm)
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plants flowering, percentage of plants with abnormal flowers, percentage of blind plants, and percentage of plants not emerging was conducted using Chi-square tests. Analyses were based on the incidence and not the actual percentages. 3. Results 3.1. Pre-transplant 3.1.1. Shoot length For experiment 1, storage in 1% O2 inhibited shoot elongation compared to air, irrespective of light conditions (Table 1, Fig. 1). Peat promoted elongation com-
pared to dry storage, with the effect being greater on bulbs also stored in air. Darkness slightly promoted elongation. Results were similar for experiment 2, with the effect of darkness being greatest on bulbs also stored with peat. 3.1.2. Percentage fresh weight loss or gain For experiment 1, storage atmosphere had no effect on percent fresh weight loss or gain (Table 1). Dry storage caused percent fresh weight losses compared to storage with peat, irrespective of atmosphere and light. Light promoted fresh weight loss with the effect being greater on bulbs also stored with peat. For experiment 2, the significant three-way interaction indicated that light only promoted fresh weight loss on bulbs also stored with both peat and air. Also, 1% O2 increased fresh weight loss, but only on bulbs also stored in darkness with peat. As in experiment 1, dry storage caused percent fresh weight losses compared to storage with peat, irrespective of atmosphere and light. 3.1.3. Number of flower buds and size (length in mm) of the largest flower bud Storage in air increased flower bud number and size compared to 1% O2 in both experiments, with the effect being enhanced by peat (Table 1). Light had no effect on flower bud number or size, and no flower buds were formed in 1% O2 (Table 1, Fig. 2). 3.2. Post-transplant 3.2.1. Days to anthesis None of the bulbs stored with a combination of light, peat, and air flowered; therefore, ANOVA and subsequent interactions could not be determined. ANOVA was conducted on the effects of moisture and atmosphere of bulbs stored in darkness. Storage in 1% O2 delayed anthesis, irrespective of moisture conditions in both experiments (Table 2). Also, peat delayed anthesis in air, but had no effect in 1% O2 .
Fig. 1. Bulbs of Asiatic hybrid lily cv. Marseille held under various combinations of light, peat, and atmosphere for 24 days (L to R: untreated control, air + peat, air – peat, 1% O2 + peat, 1% O2 – peat).
3.2.2. Total number of flower buds (healthy and aborted) and number of aborted flower buds For experiment 1, the three-way interaction was significant; however, storage in 1% O2 decreased flower bud number compared to air, irrespective of moisture and light conditions (Table 2). There was no three-way
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interaction in experiment 2, but the effects of 1% O2 were similar to experiment 1. Wilcoxon rank sum scores were used to determine main effects of light, moisture, and atmosphere on the number of aborted flower buds (Table 2). For both experiments storage in light, peat, and air, increased the number of aborted buds. 3.2.3. Height at flowering For both experiments, the three-way interaction was significant. Storage in 1% O2 increased height at flowering compared to air for bulbs stored with light, irrespective of moisture conditions (Table 2, Figs. 3 and 4). Storage in 1% O2 had no promotive effect on the height at flowering of bulbs stored with darkness, and 1% O2 actually resulted in shorter plants compared to air when bulbs were stored with both darkness and peat. 3.2.4. Percentage of plants flowering, percentage of plants with distorted flowers, percentage of blind plants, and percentage of plants not emerging The high incidence of flower abortion on plants grown from bulbs stored in light, peat, and air together, subsequently resulted in 0% of the plants flowering (Table 3). In addition, experiment 1 bulbs stored in darkness with 1% O2 and peat produced a high percentage of blind plants compared with untreated controls (33.3%; Table 3), decreasing the percentage of plants flowering. Flower abnormalities were expressed as pistil and stamen malformation or incomplete development of these organs. In experiment 1, significant distortion occurred on flowers of bulbs stored in air, while in experiment 2, flower distortion was observed in all treatments including untreated controls. Interestingly in experiment 2, storage with peat decreased the percentage of plants with flower distortion.
Fig. 2. Shoot meristems of bulbs of Asiatic hybrid lily cv. Marseille following ca. 24 days of dry sale storage without peat: 1% O2 + light (A) (red dye used for contrast), air + light (B), air + darkness (C).
3.2.5. Total number of nodes (above and below the soil) and the total number of leaves Light, moisture, or atmosphere did not affect the total number of nodes which averaged 179 (experiment 1) and 167 (experiment 2), respectively (Table 4). For experiment 1, 1% O2 produced plants with fewer leaves compared with air on bulbs stored with peat. No interactions were observed in experiment 2.
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Light
Peat
Atm
controla
Untreated + − + + + − + + − − − + − − − + LSD0.05 Light (L) Peat (P) Atm (A) L×A L×P P×A L×P×A a b
1% 1% air air 1% 1% air air
O2 O2
O2 O2
Days to anthesis
No. of flower buds
No. of aborted buds
Height at anthesis (cm)
Experiment 1
Experiment 2
Experiment 1
Experiment 2
Experiment 1
Experiment 2
Experiment 1
Experiment 2
87.3 105.7 105.9 62.6 – 106.6 105.2 74.0 60.8 3.01 – *** *** – – *** –
57.3 72.0 66.4 52.0 – 67.7 63.6 44.2 32.2 2.91 – *** *** – – ** –
5.9 2.5 2.9 6.7 5.2 2.9 3.1 6.8 7.4 0.9 *** NS *** * ** * ***
5.8 4.1 2.3 4.7 5.4 4.5 3.2 5.8 6.7 0.91 *** * *** NS NS *** NS
0.0 0.0 0.0 2.6 5.3 0.0 0.0 0.1 1.5 0.87 ***b * *** – – – –
0.0 0.0 0.7 1.5 5.4 0.0 0.7 0.3 2.7 0.92 **b *** *** – – – –
84.5 46.1 45.2 29.9 12.6 43.6 40.0 44.5 54.7 3.94 *** ** *** *** *** NS ***
60.0 34.0 22.1 20.7 10.9 36.3 29.1 33.1 38.1 4.5 *** ** *** * *** *** *
Bulbs that remained at 1 ◦ C and received no CA treatment. Means are included for comparison only and are not included in statistical analysis. Significance based on Wilcoxon rank sum scores.
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Table 2 Effects of light, moisture, and atmosphere on post-transplant flower development parameters and height at anthesis of Asiatic hybrid lily cv. Marseille following a 35 day (experiment 1) or 24 day (experiment 2) storage period
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in darkness (Table 4, Fig. 3). Also, 1% O2 increased total plant leaf area compared to air of bulbs stored dry but not with peat. As observed in experiment 1, darkness increased total plant leaf area of bulbs stored in air but had not in 1% O2 . Again, Interactions for area per individual leaf were nearly identical to those observed for total plant leaf area.
4. Discussion
Fig. 3. Plants of Asiatic hybrid lily cv. Marseille grown from bulbs held under various combinations of light, peat, and atmosphere for 35 days (L to R: untreated control, air + peat, air – peat, 1% O2 + peat, 1% O2 – peat).
3.2.6. Total plant leaf area and area per individual leaf For experiment 1, storage in 1% O2 produced plants with greater total plant leaf area compared to air, with the effect being greater on bulbs also stored with light or stored dry (Table 4, Fig. 3). Darkness increased total plant leaf area of bulbs stored in air but had no effect on bulbs stored in 1% O2 . Interactions for area per individual leaf were nearly identical to those observed for total plant leaf area. For experiment 2, 1% O2 increased total plant leaf area compared to air of bulbs stored with light, but not
An earlier study with Asiatic lily bulbs demonstrated that 1–2% O2 in a humidified storage atmosphere inhibited development and improved overall plant quality compared to storage in air at warm temperatures (22–26 ◦ C) with fluorescent light. (Legnani et al., 2004). In the following study we investigated the interactions of light and moisture (peat moss ca. 70% water content) with storage atmosphere. Shoot elongation was greatest in combined storage conditions of darkness, peat, and air, but 1% O2 suppressed shoot elongation even under conditions of high moisture and darkness. Leaf expansion was greater with peat than without peat and increased overall shoot lengths of low O2 treatments in which the leaves did not unfold. Peat and darkness inhibited fresh weight loss. Reduced water loss in darkness is likely attributed to reduced stomatal activity, with light triggering stomatal opening and water loss via transpiration (Nobel, 1999). In experiment 2, the storage of bulbs with 1% O2 increased fresh weight losses but the effect was minimal. The cause of this fresh weight loss with 1% O2 is unknown. Mikulska and Maleszewski (1990) showed that 2% O2 did not influence stomatal opening in leaves of bean (Phaseolus vulgaris L.). Storage in light without peat resulted in greatest fresh weight losses of 13–15%; however, the bulbs were not adversely affected in terms of viability and emergence. Inspection of meristems prior to transplanting showed that no floral differentiation was observed under 1% O2 , regardless of light and moisture conditions, and this phenomenon subsequently delayed anthesis. We observed similar O2 dependent flower bud inhibition in our previous study (Legnani et al., 2004). We consider this inhibition to be beneficial as it delays flower bud formation until conditions are adequate to support healthy development (i.e.,
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Fig. 4. Effects of light, peat, and atmosphere during dry sale storage on the weekly height of Asiatic hybrid lily cv. Marseille following transplanting. Each data point represents the average height of 16 plants ±S.E. Symbols are untreated controls (䊏), air + peat (䊉), air – peat (䊊), 1% O2 + peat (䉱), 1% O2 – peat ().
until after the bulb is planted in the ground). Low O2 inhibition of flower bud development has been reported in chrysanthemum plants (Chrysanthemum × morifolium Ramat.) and highbush and rabbiteye blueberry (Vaccinium corymbosum L.; V. ashei Reade) (Konjoian et al., 1983; Makus, 1991). Peat accelerated flower bud development in air and therefore increased pre-plant flower bud number. Storage in air accelerated anthesis and resulted in more flowers compared to storage in 1% O2 . Anthesis was further accelerated by storage with peat; however the effects of peat on final flower bud number were inconclusive. Earlier studies on the effects of peat moisture on lily bulbs focused on conditions during case pre-cooling at vernalizing temperatures. Prince and Cunningham (1990) reported that peat water content did not affect Easter lily flower number, and that the effects on days to flower were non-significant for some years and significant for others. Laiche and Box (1970) observed no difference on flower number of
‘Harson’ lily bulbs pre-cooled for six weeks in “damp” (68% water content) or “dry” (8% water content) peat moss, but the bulbs stored with moist peat flowered 18 days earlier compared with bulbs stored with “dry” peat. Stuart (1954) reported that storage of non-cooled Easter lily bulbs with moist peat at 7.2 ◦ C for 6–8 weeks increased flower number and decreased days to flower. It is, however, difficult to directly compare our results with earlier studies on non-cooled bulbs. Bulbs in our study were fully vernalized prior to treatment and storage temperatures reported in other studies were considerably lower compared with ours. Light conditions did not affect pre-transplant flower bud number but storage in darkness often increased final flower bud number. In contrast, Heins et al. (1982a,b) found that light stress (including total darkness) for up to 45 days after emergence did not affect flower bud number and days to flower of Easter lily. Flower bud abortion was promoted by storage with air, peat, and light. Flower bud abortion in our previous
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Table 3 Effects of light, peat, and atmosphere combinations on the percentage of plants flowering, percentage of plants with distorted flowers, and percentage of blind plants of Asiatic hybrid lily cv. Marseille following a 35 day (experiment 1) or 24 day (experiment 2) storage period Light
Peat
Atm
controla
Untreated + − + + + − + + − − − + − − − + a b
1% 1% Air Air 1% 1% Air Air
O2 O2
O2 O2
% of plants flowering
% of plants with distorted flowers
% of blind plants
Experiment 1
Experiment 2
Experiment 1
Experiment 2
Experiment 1
Experiment 2
100.0 100.0NS,b 100.0NS 73.3∗ 0.0∗∗∗ 100.0NS 66.7∗ 93.3NS 80.0NS
93.8 87.5NS 68.8NS 81.3NS 0.0∗∗∗ 100.0NS 75.0NS 100.0NS 62.5∗
0.0 0.0NS 0.0NS 81.8∗∗∗ – 0.0NS 0.0NS 92.9∗∗∗ 100.0∗∗∗
75.0 71.4NS 4.5NS 76.9NS – 56.3NS 25.0∗∗ 68.8NS 30.0∗
0.0 0.0NS 0.0NS 0.0NS 0.0NS 6.7NS 33.3∗ 0.0NS 0.0NS
0.0 0.0NS 0.0NS 0.0NS 0.0NS 0.0NS 6.3NS 0.0NS 0.0NS
Bulbs that remained at 1 ◦ C and received no CA treatment. Significantly or not significantly different to untreated control as determined by Chi-square test.
Table 4 Effects of light, peat, and atmosphere on foliage development of Asiatic hybrid lily cv. Marseille following a 35 day (experiment 1) or 24 day (experiment 2) storage period Light
Peat
Atm
controla
Untreated + − + + + − + + − − − + − − − + LSD0.05 Light (L) Peat (P) Atm (A) L×A L×P P×A L×P×A
1% 1% Air Air 1% 1% Air Air
O2 O2
O2 O2
Number of leaves
Total plant leaf area (cm2 )
Area per individual leaf (cm2 )
Experiment 1
Experiment 2
Experiment 1
Experiment 2
Experiment 1
Experiment 2
151.3 135.6 126.1 129.5 148.4 134.8 124.8 141.6 150.5 11.49 NS NS *** NS NS ** NS
151.1 132.9 145.0 137.8 146.5 145.7 143.0 153.1 162.9 10.16 ** * ** NS NS NS NS
1064.0 815.8 658.8 332.9 315.2 815.5 510.7 532.6 430.4 90.39 NS *** *** *** * ** NS
780.0 477.9 232.2 220.3 133.3 496.6 318.9 494.5 420.3 91.64 *** *** * *** NS * NS
7.1 6.0 5.2 2.6 2.1 6.0 4.1 3.7 2.8 0.54 NS *** *** *** * * NS
5.2 3.5 4.6 1.6 0.9 3.4 2.2 3.2 2.6 0.61 *** *** ** *** NS * NS
a Bulbs that remained at 1 ◦ C and received no CA treatment. Means are included for comparison only and are not included in statistical analysis.
study was also greater in bulbs stored with air compared to 1% O2 (Legnani et al., 2004). This abortion likely resulted from flower bud development during the storage period, i.e., in the absence of adequate light and nutrition for proper growth and development. The effects of low light stress on lily flower bud abortion are undefined (Heins et al., 1982a,b; Miller and Langhans, 1989a,b; Wilkins et al., 1986). In this study,
storage with light increased the incidence of bud abortion and the percent of plants flowering, perhaps a result of photo-damage; visible flower buds of bulbs stored in the light and air prior to planting contained chlorophyll (Fig. 2). Transfer of these bulbs to the high light greenhouse environment may have caused injury. Steffen and Palta (1989) showed that conditions that reduced light harvesting and/or increased energy
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utilization offered greater protection from damage due to rapid changes in light. Flower buds of bulbs stored in darkness have essentially no light harvesting capacity, thus should not suffer photo-damage when moved to a high light environment. Also, plant tissues developing with low light environments have smaller pools of xanthophylls and their intermediates, limiting their ability to dissipate excess light energy (Demmig-Adams and Adams, 1992). No direct relationship between the observed flower abnormalities and storage conditions could be made as they also appeared on untreated controls (experiment 2). Similar flowering abnormalities were observed on ‘Marseille’ in our previous study, but again, no direct correlation between storage atmospheres could be made (Legnani et al., 2004). One of the more striking results was the effect of the interaction of light and atmosphere on height at flowering. Storage in 1% O2 resulted in taller plants compared to air when bulbs were stored with light; however, 1% O2 had no effect, or the opposite effect (depending on moisture conditions) on bulbs stored in the dark. It is not known how light and O2 concentrations affect bulb phytohormone levels and sensitivity. Photomorphogenic and phytohormone responses are closely integrated and hypoxia can also influence phytohormone action (Armstrong et al., 1994). After storage, plants in experiment 2 developed much faster than those in experiment 1 due to higher greenhouse temperatures and light levels (summer versus winter conditions) and were considerably shorter. Lee and Roh (2001) observed that high greenhouse temperatures in the summer accelerated flowering and produced shorter Oriental hybrid lilies. Total plant leaf area is a function of leaf number and the area per individual leaf. The total number of nodes was unaffected by light, peat, or atmosphere, indicating that vernalization requirements had been met prior to treatment and that flower induction had occurred. Total plant leaf area was influence primarily by the area per individual leaf as indicated by the nearly identical interactions for the two parameters. One percent O2 increased total leaf area irrespective of light and moisture in experiment 1, but in experiment 2, 1% O2 had no effect in darkness plus dry storage, and actually decreased total leaf area of bulbs store in darkness with peat. Prince and Cunningham (1991) observed that ex-
posure of Easter lily bulbs to low O2 atmospheres prior to and after vernalization, decreased basal leaf size of the subsequent plants. Perhaps bulbs stored in 1% O2 are adversely affected when grown in an environment that encourages rapid growth, and therefore, the beneficial effects of darkness, which increased total leaf area in both experiments, were more conspicuous under such conditions. Red and blue light have been shown to promote leaf expansion (Van Volkenburgh, 1999), and light-triggered leaf expansion, concomitant with limited resources, would result in stunted leaves. Storage with peat was usually detrimental to leaf expansion during growth. Prince and Cunningham (1990) reported that the use of polyethylene lined cases during handling and vernalization of Easter lily bulbs decreased basal leaf size. Presumably, the polyethylene increased the moisture content. Leaf expansion ceases in unfavorable conditions, but can resume when proper resources are made available (Chapin, 1991; Palmer et al., 1996). Overall, total leaf area was lower in experiment 2, likely due to the higher greenhouse temperatures. Seleznoyva and Greer (2001) demonstrated that high temperatures shorten the growth window for leaf expansion of kiwifruit (Actinidia deliciosa). We propose that dry storage, storage with 1% O2 , and storage in darkness can delay active leaf expansion and the onset of the growth window until resources are more readily available, thus resulting in larger leaves. When stored with light, bulbs stored in a low O2 atmosphere produce plants of better quality (fewer aborted buds, greater height and foliage development) compared to bulbs stored in air; however, quality of plants grown from CA bulbs was still inferior to the untreated controls. This raises concerns of possible post hypoxic stress. Free radical generation in anoxic tissues following re-exposure to air can be detrimental to plant cells (Pfister-Sieber and Brändle, 1994) and inhibit plant growth.
5. Conclusion Storage conditions for bulbs that promote pre-plant development (high moisture, atmospheric O2 levels, and light) adversely affect final plant quality. One percent O2 prevented pre-plant development irrespective of moisture and light conditions, and the relative
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humidity inside a sealed MAP should be high enough to forgo the need to use moist peat moss to prevent desiccation, thus avoiding excess moisture that encourages growth. Storage in darkness was beneficial, particularly for bulbs stored with air; however, if total darkness were required, it would not be practical from a marketing standpoint. Therefore, storage in a low-oxygen MAP may be a practical option for improving shelf life of dry-sale hybrid lily bulbs and warrants further investigation. Future studies will investigate the developmental effects of elevated CO2 levels that would occur in a MAP engineered to maintain O2 concentration between 1 and 2%. Acknowledgements The authors acknowledge the Royal Dutch Wholesalers Association for Flower Bulbs and Nursery Stock and the Herman Schenkel Kenneth Post Foundation for financial support and plant material, and Jackie Nock for assistance with gas mixing and analysis.
References Armstrong, W., Brandle, R., Jackson, M.B., 1994. Mechanisms of flood tolerance in plants. Acta Bot. Neerl. 43, 307–358. Chapin, S.F., 1991. Integrated responses of plants to stress. Bioscience 41, 29–36. Demmig-Adams, B., Adams, W.W., 1992. Photoprotection and other responses of plants to high light stress. Annu. Rev. Plant Physiol. Plant Mol. Biol. 43, 599–626. De Hertogh, A.A., Rasmussen, H.P., Blakely, N., 1976. Morphological changes and factors influencing shoot apex development of Lilium longiflorum Thunb. during forcing. J. Am. Soc. Hort. Sci. 101, 463–471. Heins, R.D., Pemberton, H.B., Wilkins, H.F., 1982a. The influence of light on lily (Lilium longiflorum Thunb.). I. Influence of light intensity on plant development. J. Am. Soc. Hort. Sci. 107, 330–334. Heins, R.D., Wilkins, H.F., Healy, W.E., 1982b. The influence of light on lily (Lilium longiflorum Thunb.). II. Influence of photoperiod and light stress on flower number, height, and growth rate. J. Am. Soc. Hort. Sci. 107, 335–338. Konjoian, P.S., Staby, G.L., Tayama, H.K., 1983. The growth and development of Chrsyanthemum × morifolium ‘Bright Golden Anne’ with low-oxygen environments. J. Am. Soc. Hort. Sci. 108, 582–585. Laiche, A.J., Box, C.O., 1970. Response of Easter lily to bulb treatments of precooling, packing media, moisture, and gibberellin. HortScience 5, 396–397.
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Lee, J.S., Roh, M.S., 2001. Influence of frozen storage duration and forcing temperature on flowering of Oriental hybrid lilies. HortScience 36, 1053–1056. Legnani, G., Watkins, C.B., Miller, W.B., 2004. Low oxygen affects the quality of Asiatic hybrid lily bulbs during dry sale storage and subsequent forcing. Postharv. Biol. Technol. 32, 223–233. Makus, D.J., 1991. Low-oxygen atmosphere suppresses flowering in chilling satisfied blueberries. HortScience 26, 1421. Mikulska, M., Maleszewski, S., 1990. Oxygen at high concentrations reduces the response of Phaseolus stomata to light. Photosynthetica 24, 607–612. Miller, W.B., Langhans, R.W., 1989a. Reduced irradiance affects dry weight partitioning in Easter lily. J. Am. Soc. Hort. Sci. 114, 306–309. Miller, W.B., Langhans, R.W., 1989b. Carbohydrate changes of Easter lilies during growth in normal and reduced irradiance environments. J. Am. Soc. Hort. Sci. 114, 310–315. Nobel, P.S. (Ed.), 1999. Physiochemical and Environmental Plant Physiology. Academic Press, San Diego, pp. 298–302. Palmer, S.J., Berridge, D.M., McDonald, A.J.S., Davies, W.J., 1996. Control of leaf expansion in sunflower (Helianthus annus L.) by nitrogen nutrition. J. Exp. Bot. 47, 359–368. Pfister-Sieber, M., Brändle, R., 1994. Aspects of plant behaviour under anoxia and post-anoxia. Proc. R. Soc. Edinburgh 102B, 313–324. Prince, T.A., Cunningham, M.S., 1991. Forcing characteristics of Easter lily bulbs exposed to elevated ethylene and carbon dioxide and low-oxygen atmospheres. J. Am. Soc. Hort. Sci. 116, 63–67. Prince, T.A., Cunningham, M.S., 1990. Response of Easter lily bulbs to peat moisture content and the use of peat or polyethylene-lined cases during handling and vernalization. J. Am. Soc. Hort. Sci. 115, 68–72. Seleznoyva, A.N., Greer, D.H., 2001. Effects of temperature and leaf position on leaf area expansion of kiwifruit (Actinidia deliciosa) shoots: development of a modeling framework. Ann. Bot. 88, 605–615. Steffen, K.L., Palta, J.P., 1989. Growth and development temperature influences level of tolerance to high light stress. Plant Physiol. 91, 1558–1561. Stuart, N.W., Chester, S.P., Gould, C.J., 1970. The influence of controlled atmospheres during cool storage on the subsequent flowering of Easter lilies and bulbous iris. HortScience 5, 356. Stuart, N., 1954. Moisture content of packing medium, temperature and duration of storage as factors in forcing lily bulbs. Proc. Soc. Hort. Sci. 63, 488–494. Thornton, N.C., Imle, E.P., 1941. Effect of mixtures of oxygen and carbon dioxide on the development of dormancy in Easter lilies. Proc. Soc. Hort. Sci. 38, 708. Thornton, N.C., 1939. Development of dormancy in lily bulbs. Contrib. Boyce Thompson Inst. 10, 381–388. Van Volkenburgh, E., 1999. Leaf expansion—an integrating plant behaviour. Plant Cell Environ. 22, 1463–1473. Wilkins, T.C., Grueber, K., Healy, W., Pemberton, H.B., 1986. Minimum fluorescent light requirements and ancymidol interactions on the growth of Easter lily. J. Am. Soc. Hort. Sci. 111, 384–387.
Light, moisture, and atmosphere interact to affect the quality of dry-sale lily bulbs Garry Legnani, Christopher B. Watkins, William B. Miller∗ Department of Horticulture, Cornell University, Ithaca, NY 14853, USA Received 22 May 2003; accepted 15 February 2004
Abstract The interactions of moisture and light with low oxygen (1%) storage of dry sale lily bulbs at 22–25 ◦ C for 4–5 weeks have been studied as part of a continuing evaluation of modified atmospheres (MA) to lengthen shelf life. Conditions that promoted development in storage (light, moisture, and air) were detrimental to final plant quality, resulting in short plants with many aborted flowers and poor foliage development. One percent O2 suppressed pre-plant development compared to storage in air, irrespective of light and moisture. When bulbs were forced under conditions that accelerated growth (high temperatures and light), bulbs stored in darkness, air, and dry (without peat) were comparable in quality (producing normal flowers and having adequate height and foliage development) to bulbs stored with 1% O2 without peat. Exclusion of light is beneficial to bulbs stored in air but is not practical for marketing. The quality of dry-sale bulbs was always inferior to un-treated control bulbs that remained in the cooler during the dry-sale storage period. Untreated bulbs produced taller plants with more flowers and superior foliage development compared to bulbs stored under dry-sale conditions, regardless of the combination of light, moisture, and atmosphere. © 2004 Elsevier B.V. All rights reserved. Keywords: Lilium bulbs; Low oxygen; Moisture; Light; Flowering; Leaf area
1. Introduction In a previous study, we reported an evaluation of the use of modified atmospheres (MA) to extend the shelf life of dry sale lily bulbs (Legnani et al., 2004). The study examined the tolerance of bulbs to storage under low O2 for ca. 30 days at warm temperatures (22–26 ◦ C) with fluorescent light. These ∗ Corresponding author. Tel.: +1 607 255 1799; fax: +1 607 255 9998. E-mail address: [email protected] (W.B. Miller).
temperature and light conditions were chosen to simulate a retail situation in which vernalized bulbs are packaged and displayed in a garden center for springtime sales leading to planting in the garden. The goal is to develop a MA package (MAP) to limit shoot elongation and flower development under dry sale conditions while maintaining bulb viability and the ability to produce a commercially acceptable flowering plant for consumers. The study showed that humidified atmospheres of 1–2% O2 inhibited shoot elongation and flower bud development in three Asiatic hybrid lily cultivars. Overall, plant quality
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was improved by low O2 storage, but varied with cultivar. Commercially, bulbs are often packaged with moist peat moss to minimize physical damage during transport and to prevent desiccation. Since both peat moss moisture content and retail lighting conditions can vary widely, their interactions with O2 concentration are of critical interest to this research. Studies on the effects of controlled atmospheres (CA) (Thornton, 1939; Thornton and Imle, 1941; Stuart et al., 1970; Prince and Cunningham, 1991) and packaging media moisture content (Stuart, 1954; Laiche and Box, 1970; Prince and Cunningham, 1990) have been reported on Easter lily (Lilium longiflorum Thunb.). These studies focused on storage conditions during commercial case handling, vernalization, and their effects on forcing characteristics. Other studies on Easter lily have reported the effects of light intensity on forcing characteristics, dry weight partitioning, and carbohydrate changes (Heins et al., 1982a,b; Wilkins et al., 1986; Miller and Langhans, 1989a,b). To our knowledge no information exists on how these factors influence packaged bulbs in a retail situation. In this paper, we report on the interactions of storage atmosphere, moisture, and light during dry-sale storage of hybrid lily bulbs.
2. Materials and methods 2.1. Experiment 1 2.1.1. Plant material Previously frozen Asiatic hybrid lily bulbs (12/14 cm) (Lilium asiaticum cv. Marseille) were received on 9 September. Bulbs were stored in the dark (1 ◦ C) in their original polyethylene-film-lined containers, with moist peat moss. On 18 October, bulbs were sorted by size with average shoot lengths external to the bulb (±S.E.) of 1.00 ± 0.09 cm. Five bulbs were randomly selected and meristems were examined using a dissecting scope. Meristems were at the pre-floral stage as defined by De Hertogh et al. (1976). 2.1.2. Simulated dry-sale storage Bulbs were placed in cardboard egg-cartons inside 20 l jars. The cartons allowed for an upright orientation of the bulbs. Two egg-cartons, each holding an
experimental unit of 6 bulbs, were placed in each jar. Fresh weights of the experimental units were determined prior to placement in the jars. One egg-carton was enclosed in a polyethylene bag with enough moist peat moss (ca. 75% water content) to cover the bulb scales (peat or no peat treatment). The bags were used to hold the peat moss in place and were not sealed. Jars were either covered with aluminum foil or left uncovered (light or dark treatment) then exposed to humidified atmospheres of air or 1% O2 balanced with nitrogen. Humidified atmospheres were applied using a capillary flow board system at a flow rate of 100 ml/min. Four jars (repetitions) per treatment were arranged in a randomized block three-way factorial design on four shelves within a controlled temperature chamber (21 ◦ C) with fluorescent light. Temperature and relative humidity (RH) inside the jars was monitored using a HOBO Pro temperature and RH recorder (Onsight Computer, Bourne, MA). Temperatures inside the jars averaged 22 ◦ C (foil covered) and 23 ◦ C (uncovered) and RH was ca. 85%. Photosynthetic photon flux density (PPFD) inside uncovered jars at the level of the bulbs was ca. 45 mol m−2 s−1 . The 1% O2 atmosphere was monitored daily using gas chromatography (model 1200 gas partitioner, Fisher Scientific, Springfield, NJ). The percentage of O2 (±S.E.) was 0.97 ± 0.06%. After 35 days, bulbs were removed from the jars and shoot lengths and fresh weights determined. The shoots of two bulbs from each experimental unit were dissected and the meristems examined. The number of flower buds and the size (length in mm) of the largest bud were determined. 2.1.3. Greenhouse forcing The remaining bulbs were planted in 15 cm pots in a 1:2:1 (soil:peat:perlite) mix and placed in a glass greenhouse for forcing. Plants were arranged in a completely randomized design (16 plants per treatment). Bulbs that remained in the cooler (1 ◦ C) without air or low O2 treatments were planted as untreated controls. The greenhouse temperature set point was 20 ◦ C with max/min temperatures reaching 22 ◦ C day and 17 ◦ C night, respectively. Plants were grown with a standard fertilizer regime. Data collected included days to anthesis, total number of flower buds (healthy and aborted), aborted flower buds, and height at flowering (from the rim of the pot to the top of the plant). Additional data included percentage of plants flowering,
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percentage of plants with abnormal flowers, percentage of blind plants (plants not producing flower buds), and percentage of plants not emerging. After all plants in a treatment had flowered, 10 plants were randomly chosen and the total number of nodes (above and below the soil to just below the first pedicle), total number of leaves, total leaf area, and area per individual leaf were determined. 2.2. Experiment 2 2.2.1. Plant material Previously frozen Asiatic hybrid lily bulbs (12/14 cm) cv. Marseille were received on 24 May. Bulbs were stored at 4 ◦ C as previously described. On 4 June, bulbs were sorted by size with average shoot lengths external to the bulb (±S.E.) of 1.80 ±0.11 cm. Meristems were vegetative or at the pre-floral stage. 2.2.2. Simulated dry-sale storage Bulbs were arranged in 20 l jars using the same experimental design as experiment 1. Temperatures inside the jars averaged 24 ◦ C (foil covered) and 25 ◦ C
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(uncovered) and RH was ca. 85%. The percentage of O2 (±S.E.) was 1.10 ± 0.04%. After 24 days, bulbs were removed from the jars and shoot lengths and fresh weights determined and the meristems of two bulbs from each experimental unit were examined as previously described. 2.2.3. Greenhouse forcing The remaining bulbs were planted as previously described. The greenhouse temperature set point was 20 ◦ C day/night with max/min temperatures reaching 27 ◦ C day and 17 ◦ C night, respectively. Plant culture and data collection were as previously described. 2.3. Statistical analyses Analysis of variance (ANOVA) for subsequent interactions was conducted using SAS (Cary, NC). When assumptions for ANOVA could not be met, main effects were analyzed using the Wilcoxon rank sum scores. The least significant difference (L.S.D.) is provided for mean separation. Comparison of dry-sale treatments to untreated controls for percentage of
Table 1 Effects of light, moisture, and atmosphere on pre-transplant growth and development of Asiatic hybrid lily cv. Marseille following a 35 day (experiment 1) or 24 day (experiment 2) storage period Light
Peat
+ − + + + − + + − − − + − − − + LSD0.05 Light (L) Peat (P) Atm (A) L×A L×P P×A L×P×A a b
Atm
1% 1% Air Air 1% 1% Air Air
O2 O2
O2 O2
Shoot length (cm)
Fresh weight loss (−) or gain (+) (%)
Number of flower buds
Experiment 1
Experiment 2
Experiment 1
Experiment 2
Experiment 1
Experiment 2
Experiment 1
Experiment 2
1.6a 3.5 5.6 17.9 2.3 6.4 5.8 20.1 1.78 * *** *** NS NS *** NS
1.8a 5.2 3.3 16.6 2.4 7.3 3.8 22.7 1.58 *** *** *** NS ** *** NS
−13.0a −2.3 −14.5 −4.0 −9.5 +4.5 −11.3 +7.3 2.75 *** *** NS NS ** NS NS
−14.9a +5.2 −13.9 +5.2 −8.5 +5.1 −9.0 +19.6 5.27 ** *** * NS NS * *
0.0b 0.0 3.0 5.8 0.0 0.0 3.8 5.0 1.54 NS * *** NS NS * NS
0.0b 0.0 2.8 5.9 0.0 0.0 2.9 5.8 2.66 NS *** *** NS NS *** NS
0.0b 0.0 2.0 5.5 0.0 0.0 1.3 3.0 1.35 NS ** *** NS NS ** NS
0.0b 0.0 1.8 4.0 0.0 0.0 1.6 4.3 0.82 NS *** *** NS NS *** NS
Means represent the average of four replications with six bulbs per experimental unit. Means represent the average of four replications with two bulbs per experimental unit.
Size of largest flower bud (length in mm)
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plants flowering, percentage of plants with abnormal flowers, percentage of blind plants, and percentage of plants not emerging was conducted using Chi-square tests. Analyses were based on the incidence and not the actual percentages. 3. Results 3.1. Pre-transplant 3.1.1. Shoot length For experiment 1, storage in 1% O2 inhibited shoot elongation compared to air, irrespective of light conditions (Table 1, Fig. 1). Peat promoted elongation com-
pared to dry storage, with the effect being greater on bulbs also stored in air. Darkness slightly promoted elongation. Results were similar for experiment 2, with the effect of darkness being greatest on bulbs also stored with peat. 3.1.2. Percentage fresh weight loss or gain For experiment 1, storage atmosphere had no effect on percent fresh weight loss or gain (Table 1). Dry storage caused percent fresh weight losses compared to storage with peat, irrespective of atmosphere and light. Light promoted fresh weight loss with the effect being greater on bulbs also stored with peat. For experiment 2, the significant three-way interaction indicated that light only promoted fresh weight loss on bulbs also stored with both peat and air. Also, 1% O2 increased fresh weight loss, but only on bulbs also stored in darkness with peat. As in experiment 1, dry storage caused percent fresh weight losses compared to storage with peat, irrespective of atmosphere and light. 3.1.3. Number of flower buds and size (length in mm) of the largest flower bud Storage in air increased flower bud number and size compared to 1% O2 in both experiments, with the effect being enhanced by peat (Table 1). Light had no effect on flower bud number or size, and no flower buds were formed in 1% O2 (Table 1, Fig. 2). 3.2. Post-transplant 3.2.1. Days to anthesis None of the bulbs stored with a combination of light, peat, and air flowered; therefore, ANOVA and subsequent interactions could not be determined. ANOVA was conducted on the effects of moisture and atmosphere of bulbs stored in darkness. Storage in 1% O2 delayed anthesis, irrespective of moisture conditions in both experiments (Table 2). Also, peat delayed anthesis in air, but had no effect in 1% O2 .
Fig. 1. Bulbs of Asiatic hybrid lily cv. Marseille held under various combinations of light, peat, and atmosphere for 24 days (L to R: untreated control, air + peat, air – peat, 1% O2 + peat, 1% O2 – peat).
3.2.2. Total number of flower buds (healthy and aborted) and number of aborted flower buds For experiment 1, the three-way interaction was significant; however, storage in 1% O2 decreased flower bud number compared to air, irrespective of moisture and light conditions (Table 2). There was no three-way
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interaction in experiment 2, but the effects of 1% O2 were similar to experiment 1. Wilcoxon rank sum scores were used to determine main effects of light, moisture, and atmosphere on the number of aborted flower buds (Table 2). For both experiments storage in light, peat, and air, increased the number of aborted buds. 3.2.3. Height at flowering For both experiments, the three-way interaction was significant. Storage in 1% O2 increased height at flowering compared to air for bulbs stored with light, irrespective of moisture conditions (Table 2, Figs. 3 and 4). Storage in 1% O2 had no promotive effect on the height at flowering of bulbs stored with darkness, and 1% O2 actually resulted in shorter plants compared to air when bulbs were stored with both darkness and peat. 3.2.4. Percentage of plants flowering, percentage of plants with distorted flowers, percentage of blind plants, and percentage of plants not emerging The high incidence of flower abortion on plants grown from bulbs stored in light, peat, and air together, subsequently resulted in 0% of the plants flowering (Table 3). In addition, experiment 1 bulbs stored in darkness with 1% O2 and peat produced a high percentage of blind plants compared with untreated controls (33.3%; Table 3), decreasing the percentage of plants flowering. Flower abnormalities were expressed as pistil and stamen malformation or incomplete development of these organs. In experiment 1, significant distortion occurred on flowers of bulbs stored in air, while in experiment 2, flower distortion was observed in all treatments including untreated controls. Interestingly in experiment 2, storage with peat decreased the percentage of plants with flower distortion.
Fig. 2. Shoot meristems of bulbs of Asiatic hybrid lily cv. Marseille following ca. 24 days of dry sale storage without peat: 1% O2 + light (A) (red dye used for contrast), air + light (B), air + darkness (C).
3.2.5. Total number of nodes (above and below the soil) and the total number of leaves Light, moisture, or atmosphere did not affect the total number of nodes which averaged 179 (experiment 1) and 167 (experiment 2), respectively (Table 4). For experiment 1, 1% O2 produced plants with fewer leaves compared with air on bulbs stored with peat. No interactions were observed in experiment 2.
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Light
Peat
Atm
controla
Untreated + − + + + − + + − − − + − − − + LSD0.05 Light (L) Peat (P) Atm (A) L×A L×P P×A L×P×A a b
1% 1% air air 1% 1% air air
O2 O2
O2 O2
Days to anthesis
No. of flower buds
No. of aborted buds
Height at anthesis (cm)
Experiment 1
Experiment 2
Experiment 1
Experiment 2
Experiment 1
Experiment 2
Experiment 1
Experiment 2
87.3 105.7 105.9 62.6 – 106.6 105.2 74.0 60.8 3.01 – *** *** – – *** –
57.3 72.0 66.4 52.0 – 67.7 63.6 44.2 32.2 2.91 – *** *** – – ** –
5.9 2.5 2.9 6.7 5.2 2.9 3.1 6.8 7.4 0.9 *** NS *** * ** * ***
5.8 4.1 2.3 4.7 5.4 4.5 3.2 5.8 6.7 0.91 *** * *** NS NS *** NS
0.0 0.0 0.0 2.6 5.3 0.0 0.0 0.1 1.5 0.87 ***b * *** – – – –
0.0 0.0 0.7 1.5 5.4 0.0 0.7 0.3 2.7 0.92 **b *** *** – – – –
84.5 46.1 45.2 29.9 12.6 43.6 40.0 44.5 54.7 3.94 *** ** *** *** *** NS ***
60.0 34.0 22.1 20.7 10.9 36.3 29.1 33.1 38.1 4.5 *** ** *** * *** *** *
Bulbs that remained at 1 ◦ C and received no CA treatment. Means are included for comparison only and are not included in statistical analysis. Significance based on Wilcoxon rank sum scores.
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Table 2 Effects of light, moisture, and atmosphere on post-transplant flower development parameters and height at anthesis of Asiatic hybrid lily cv. Marseille following a 35 day (experiment 1) or 24 day (experiment 2) storage period
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in darkness (Table 4, Fig. 3). Also, 1% O2 increased total plant leaf area compared to air of bulbs stored dry but not with peat. As observed in experiment 1, darkness increased total plant leaf area of bulbs stored in air but had not in 1% O2 . Again, Interactions for area per individual leaf were nearly identical to those observed for total plant leaf area.
4. Discussion
Fig. 3. Plants of Asiatic hybrid lily cv. Marseille grown from bulbs held under various combinations of light, peat, and atmosphere for 35 days (L to R: untreated control, air + peat, air – peat, 1% O2 + peat, 1% O2 – peat).
3.2.6. Total plant leaf area and area per individual leaf For experiment 1, storage in 1% O2 produced plants with greater total plant leaf area compared to air, with the effect being greater on bulbs also stored with light or stored dry (Table 4, Fig. 3). Darkness increased total plant leaf area of bulbs stored in air but had no effect on bulbs stored in 1% O2 . Interactions for area per individual leaf were nearly identical to those observed for total plant leaf area. For experiment 2, 1% O2 increased total plant leaf area compared to air of bulbs stored with light, but not
An earlier study with Asiatic lily bulbs demonstrated that 1–2% O2 in a humidified storage atmosphere inhibited development and improved overall plant quality compared to storage in air at warm temperatures (22–26 ◦ C) with fluorescent light. (Legnani et al., 2004). In the following study we investigated the interactions of light and moisture (peat moss ca. 70% water content) with storage atmosphere. Shoot elongation was greatest in combined storage conditions of darkness, peat, and air, but 1% O2 suppressed shoot elongation even under conditions of high moisture and darkness. Leaf expansion was greater with peat than without peat and increased overall shoot lengths of low O2 treatments in which the leaves did not unfold. Peat and darkness inhibited fresh weight loss. Reduced water loss in darkness is likely attributed to reduced stomatal activity, with light triggering stomatal opening and water loss via transpiration (Nobel, 1999). In experiment 2, the storage of bulbs with 1% O2 increased fresh weight losses but the effect was minimal. The cause of this fresh weight loss with 1% O2 is unknown. Mikulska and Maleszewski (1990) showed that 2% O2 did not influence stomatal opening in leaves of bean (Phaseolus vulgaris L.). Storage in light without peat resulted in greatest fresh weight losses of 13–15%; however, the bulbs were not adversely affected in terms of viability and emergence. Inspection of meristems prior to transplanting showed that no floral differentiation was observed under 1% O2 , regardless of light and moisture conditions, and this phenomenon subsequently delayed anthesis. We observed similar O2 dependent flower bud inhibition in our previous study (Legnani et al., 2004). We consider this inhibition to be beneficial as it delays flower bud formation until conditions are adequate to support healthy development (i.e.,
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Fig. 4. Effects of light, peat, and atmosphere during dry sale storage on the weekly height of Asiatic hybrid lily cv. Marseille following transplanting. Each data point represents the average height of 16 plants ±S.E. Symbols are untreated controls (䊏), air + peat (䊉), air – peat (䊊), 1% O2 + peat (䉱), 1% O2 – peat ().
until after the bulb is planted in the ground). Low O2 inhibition of flower bud development has been reported in chrysanthemum plants (Chrysanthemum × morifolium Ramat.) and highbush and rabbiteye blueberry (Vaccinium corymbosum L.; V. ashei Reade) (Konjoian et al., 1983; Makus, 1991). Peat accelerated flower bud development in air and therefore increased pre-plant flower bud number. Storage in air accelerated anthesis and resulted in more flowers compared to storage in 1% O2 . Anthesis was further accelerated by storage with peat; however the effects of peat on final flower bud number were inconclusive. Earlier studies on the effects of peat moisture on lily bulbs focused on conditions during case pre-cooling at vernalizing temperatures. Prince and Cunningham (1990) reported that peat water content did not affect Easter lily flower number, and that the effects on days to flower were non-significant for some years and significant for others. Laiche and Box (1970) observed no difference on flower number of
‘Harson’ lily bulbs pre-cooled for six weeks in “damp” (68% water content) or “dry” (8% water content) peat moss, but the bulbs stored with moist peat flowered 18 days earlier compared with bulbs stored with “dry” peat. Stuart (1954) reported that storage of non-cooled Easter lily bulbs with moist peat at 7.2 ◦ C for 6–8 weeks increased flower number and decreased days to flower. It is, however, difficult to directly compare our results with earlier studies on non-cooled bulbs. Bulbs in our study were fully vernalized prior to treatment and storage temperatures reported in other studies were considerably lower compared with ours. Light conditions did not affect pre-transplant flower bud number but storage in darkness often increased final flower bud number. In contrast, Heins et al. (1982a,b) found that light stress (including total darkness) for up to 45 days after emergence did not affect flower bud number and days to flower of Easter lily. Flower bud abortion was promoted by storage with air, peat, and light. Flower bud abortion in our previous
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Table 3 Effects of light, peat, and atmosphere combinations on the percentage of plants flowering, percentage of plants with distorted flowers, and percentage of blind plants of Asiatic hybrid lily cv. Marseille following a 35 day (experiment 1) or 24 day (experiment 2) storage period Light
Peat
Atm
controla
Untreated + − + + + − + + − − − + − − − + a b
1% 1% Air Air 1% 1% Air Air
O2 O2
O2 O2
% of plants flowering
% of plants with distorted flowers
% of blind plants
Experiment 1
Experiment 2
Experiment 1
Experiment 2
Experiment 1
Experiment 2
100.0 100.0NS,b 100.0NS 73.3∗ 0.0∗∗∗ 100.0NS 66.7∗ 93.3NS 80.0NS
93.8 87.5NS 68.8NS 81.3NS 0.0∗∗∗ 100.0NS 75.0NS 100.0NS 62.5∗
0.0 0.0NS 0.0NS 81.8∗∗∗ – 0.0NS 0.0NS 92.9∗∗∗ 100.0∗∗∗
75.0 71.4NS 4.5NS 76.9NS – 56.3NS 25.0∗∗ 68.8NS 30.0∗
0.0 0.0NS 0.0NS 0.0NS 0.0NS 6.7NS 33.3∗ 0.0NS 0.0NS
0.0 0.0NS 0.0NS 0.0NS 0.0NS 0.0NS 6.3NS 0.0NS 0.0NS
Bulbs that remained at 1 ◦ C and received no CA treatment. Significantly or not significantly different to untreated control as determined by Chi-square test.
Table 4 Effects of light, peat, and atmosphere on foliage development of Asiatic hybrid lily cv. Marseille following a 35 day (experiment 1) or 24 day (experiment 2) storage period Light
Peat
Atm
controla
Untreated + − + + + − + + − − − + − − − + LSD0.05 Light (L) Peat (P) Atm (A) L×A L×P P×A L×P×A
1% 1% Air Air 1% 1% Air Air
O2 O2
O2 O2
Number of leaves
Total plant leaf area (cm2 )
Area per individual leaf (cm2 )
Experiment 1
Experiment 2
Experiment 1
Experiment 2
Experiment 1
Experiment 2
151.3 135.6 126.1 129.5 148.4 134.8 124.8 141.6 150.5 11.49 NS NS *** NS NS ** NS
151.1 132.9 145.0 137.8 146.5 145.7 143.0 153.1 162.9 10.16 ** * ** NS NS NS NS
1064.0 815.8 658.8 332.9 315.2 815.5 510.7 532.6 430.4 90.39 NS *** *** *** * ** NS
780.0 477.9 232.2 220.3 133.3 496.6 318.9 494.5 420.3 91.64 *** *** * *** NS * NS
7.1 6.0 5.2 2.6 2.1 6.0 4.1 3.7 2.8 0.54 NS *** *** *** * * NS
5.2 3.5 4.6 1.6 0.9 3.4 2.2 3.2 2.6 0.61 *** *** ** *** NS * NS
a Bulbs that remained at 1 ◦ C and received no CA treatment. Means are included for comparison only and are not included in statistical analysis.
study was also greater in bulbs stored with air compared to 1% O2 (Legnani et al., 2004). This abortion likely resulted from flower bud development during the storage period, i.e., in the absence of adequate light and nutrition for proper growth and development. The effects of low light stress on lily flower bud abortion are undefined (Heins et al., 1982a,b; Miller and Langhans, 1989a,b; Wilkins et al., 1986). In this study,
storage with light increased the incidence of bud abortion and the percent of plants flowering, perhaps a result of photo-damage; visible flower buds of bulbs stored in the light and air prior to planting contained chlorophyll (Fig. 2). Transfer of these bulbs to the high light greenhouse environment may have caused injury. Steffen and Palta (1989) showed that conditions that reduced light harvesting and/or increased energy
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utilization offered greater protection from damage due to rapid changes in light. Flower buds of bulbs stored in darkness have essentially no light harvesting capacity, thus should not suffer photo-damage when moved to a high light environment. Also, plant tissues developing with low light environments have smaller pools of xanthophylls and their intermediates, limiting their ability to dissipate excess light energy (Demmig-Adams and Adams, 1992). No direct relationship between the observed flower abnormalities and storage conditions could be made as they also appeared on untreated controls (experiment 2). Similar flowering abnormalities were observed on ‘Marseille’ in our previous study, but again, no direct correlation between storage atmospheres could be made (Legnani et al., 2004). One of the more striking results was the effect of the interaction of light and atmosphere on height at flowering. Storage in 1% O2 resulted in taller plants compared to air when bulbs were stored with light; however, 1% O2 had no effect, or the opposite effect (depending on moisture conditions) on bulbs stored in the dark. It is not known how light and O2 concentrations affect bulb phytohormone levels and sensitivity. Photomorphogenic and phytohormone responses are closely integrated and hypoxia can also influence phytohormone action (Armstrong et al., 1994). After storage, plants in experiment 2 developed much faster than those in experiment 1 due to higher greenhouse temperatures and light levels (summer versus winter conditions) and were considerably shorter. Lee and Roh (2001) observed that high greenhouse temperatures in the summer accelerated flowering and produced shorter Oriental hybrid lilies. Total plant leaf area is a function of leaf number and the area per individual leaf. The total number of nodes was unaffected by light, peat, or atmosphere, indicating that vernalization requirements had been met prior to treatment and that flower induction had occurred. Total plant leaf area was influence primarily by the area per individual leaf as indicated by the nearly identical interactions for the two parameters. One percent O2 increased total leaf area irrespective of light and moisture in experiment 1, but in experiment 2, 1% O2 had no effect in darkness plus dry storage, and actually decreased total leaf area of bulbs store in darkness with peat. Prince and Cunningham (1991) observed that ex-
posure of Easter lily bulbs to low O2 atmospheres prior to and after vernalization, decreased basal leaf size of the subsequent plants. Perhaps bulbs stored in 1% O2 are adversely affected when grown in an environment that encourages rapid growth, and therefore, the beneficial effects of darkness, which increased total leaf area in both experiments, were more conspicuous under such conditions. Red and blue light have been shown to promote leaf expansion (Van Volkenburgh, 1999), and light-triggered leaf expansion, concomitant with limited resources, would result in stunted leaves. Storage with peat was usually detrimental to leaf expansion during growth. Prince and Cunningham (1990) reported that the use of polyethylene lined cases during handling and vernalization of Easter lily bulbs decreased basal leaf size. Presumably, the polyethylene increased the moisture content. Leaf expansion ceases in unfavorable conditions, but can resume when proper resources are made available (Chapin, 1991; Palmer et al., 1996). Overall, total leaf area was lower in experiment 2, likely due to the higher greenhouse temperatures. Seleznoyva and Greer (2001) demonstrated that high temperatures shorten the growth window for leaf expansion of kiwifruit (Actinidia deliciosa). We propose that dry storage, storage with 1% O2 , and storage in darkness can delay active leaf expansion and the onset of the growth window until resources are more readily available, thus resulting in larger leaves. When stored with light, bulbs stored in a low O2 atmosphere produce plants of better quality (fewer aborted buds, greater height and foliage development) compared to bulbs stored in air; however, quality of plants grown from CA bulbs was still inferior to the untreated controls. This raises concerns of possible post hypoxic stress. Free radical generation in anoxic tissues following re-exposure to air can be detrimental to plant cells (Pfister-Sieber and Brändle, 1994) and inhibit plant growth.
5. Conclusion Storage conditions for bulbs that promote pre-plant development (high moisture, atmospheric O2 levels, and light) adversely affect final plant quality. One percent O2 prevented pre-plant development irrespective of moisture and light conditions, and the relative
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humidity inside a sealed MAP should be high enough to forgo the need to use moist peat moss to prevent desiccation, thus avoiding excess moisture that encourages growth. Storage in darkness was beneficial, particularly for bulbs stored with air; however, if total darkness were required, it would not be practical from a marketing standpoint. Therefore, storage in a low-oxygen MAP may be a practical option for improving shelf life of dry-sale hybrid lily bulbs and warrants further investigation. Future studies will investigate the developmental effects of elevated CO2 levels that would occur in a MAP engineered to maintain O2 concentration between 1 and 2%. Acknowledgements The authors acknowledge the Royal Dutch Wholesalers Association for Flower Bulbs and Nursery Stock and the Herman Schenkel Kenneth Post Foundation for financial support and plant material, and Jackie Nock for assistance with gas mixing and analysis.
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