Ethylene Inhibits Sprouting of Onion Bulbs during Long-term Storage

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  • 1 Kentville Research and Development Centre, Agriculture and Agri-Food Canada, 32 Main Street, Kentville, NS B4N 1J5 Canada
  • | 2 Nova Agri Inc., 1225 Middle Dyke Road, Centreville, NS B0P 1J0 Canada
  • | 3 Kentville Research and Development Centre, Agriculture and Agri-Food Canada, 32 Main Street, Kentville, NS B4N 1J5 Canada

The protrusion of sprouts is a major cause of loss of dry onions (Allium cepa L.) during extended storage. Sprouting is conventionally suppressed by treating onions with maleic hydrazide (MH) before harvest. More recently, ethylene was reported to inhibit sprout growth in stored onions, but commercial use of ethylene has been limited. Therefore, the objective of this study was to assess the effectiveness of ethylene on sprout suppression of five commercial cultivars of onions during storage and compare its effectiveness with and without MH treatment. Onions treated with MH were stored for up to 9 months at 1 °C in atmospheres with and without ethylene in a series of experiments conducted over six seasons. Differences in sprout elongation and protrusion were observed during storage in air among the five cultivars. Storage in ethylene was effective in inhibiting sprout elongation and root growth of onion bulbs in all cultivars, with concentrations of 7 µL·L−1 ethylene being more effective than 1 µL·L−1 ethylene. Delaying application of ethylene by 4 months was less effective in inhibiting sprout elongation than continuous treatment. Ethylene provided greater sprout suppression than MH treatments alone and could serve as a replacement for MH.

Abstract

The protrusion of sprouts is a major cause of loss of dry onions (Allium cepa L.) during extended storage. Sprouting is conventionally suppressed by treating onions with maleic hydrazide (MH) before harvest. More recently, ethylene was reported to inhibit sprout growth in stored onions, but commercial use of ethylene has been limited. Therefore, the objective of this study was to assess the effectiveness of ethylene on sprout suppression of five commercial cultivars of onions during storage and compare its effectiveness with and without MH treatment. Onions treated with MH were stored for up to 9 months at 1 °C in atmospheres with and without ethylene in a series of experiments conducted over six seasons. Differences in sprout elongation and protrusion were observed during storage in air among the five cultivars. Storage in ethylene was effective in inhibiting sprout elongation and root growth of onion bulbs in all cultivars, with concentrations of 7 µL·L−1 ethylene being more effective than 1 µL·L−1 ethylene. Delaying application of ethylene by 4 months was less effective in inhibiting sprout elongation than continuous treatment. Ethylene provided greater sprout suppression than MH treatments alone and could serve as a replacement for MH.

Onions (Allium cepa L.) are a popular vegetable consumed throughout the world. In the United States, onions are second only to potatoes among all vegetables sold, comprising more than 10% of total vegetables at retail based on weight (U.S. Department of Agriculture Economic Research Service, 2020). To meet demand throughout the year, onions must be stored for extended periods of time to ensure a constant supply to retail markets. Effective storage at 0 °C and 65% to 75% relative humidity (RH) can maintain good-quality bulbs for ≥5 months (Adamicki, 2016). A significant loss of marketable onions occurs during extended storage due to sprouting from dormancy break and, to a lesser extent, from decay, softening, and rooting (Adamicki, 2005).

Dormancy is the temporary suspension of visible growth of any plant organ containing a meristem and can be classified into three categories (Lang, 1987; Rohde and Bhalerao, 2007). Endodormancy initiates when the signal to suspend growth originates from the organ of interest. Paradormancy occurs in the organ of interest due to signals originating from an external organ. Ecodormancy is in response to unfavorable environmental conditions. Endo- and ecodormancy in postharvest onion bulbs are the primary regulators for arrested growth (Pak et al., 1995). Growers harvest onions once they complete the bulbing phase as highlighted by the cessation of growth and senescence of aboveground foliage. This signals that the bulbs have transitioned to an endodormant state. Bulbs transferred to cold storage remain endodormant for up to 3 weeks, after which, the bulbs break endodormancy to resume preharvest levels of cellular division and are capable of rooting (Pak et al., 1995), increased respiration (Ward and Tucker, 1976), and expansion of sprout leaves near the center of the bulb (Yasin and Bufler, 2007). The rate and timing of the resumption of growth varies significantly among cultivars but can be delayed by holding onions at 0 to 2 °C (Adamicki, 2005).

Storage can be extended by forcing onion bulbs into an ecodormant state through exposure to threshold low temperatures or from the preharvest application of chemical inhibitors such as maleic hydrazide (MH) (Adamicki, 2005; El-Otmani et al., 2003; Ilić et al., 2011). MH is a growth inhibitor that suppresses terminal meristem activity and internodal elongation of plants (Naylor and Davis, 1950). Alternative approaches for the long-term storage of produce need to be identified as the use of chemicals in food production comes under increased scrutiny.

Recently exposure of onions to ethylene during storage was reported to reduce sprouting (Bufler, 2009; Ohanenye et al., 2019), and in Europe, the use of ethylene in commercial storage is being promoted as a method of sprout suppression. In North America, the use of ethylene to inhibit sprouting of onions has received little attention. It has also not been reported how the effectiveness of ethylene inhibition on sprouting compares to that of MH treatments. Further, whether the combination of MH and ethylene has an additive effect on the reduction of sprouting has not been researched. The objective of this study was to assess the effectiveness of ethylene on the suppression of sprouting of onions during long-term cold storage and whether it can supplement or replace the more conventional MH treatment.

Material and Methods

Onions.

For a series of experiments conducted over six seasons, onions were commercially harvested from production fields from 2015 to 2020. A total of five yellow onion cultivars were assessed, which included ‘Copra’ (Bejo Seeds Inc., Geneva, NY; three seasons), ‘Mountaineer’ (American Takii, Inc., Salinas, CA; four seasons), ‘Patterson’ (Bejo Seeds Inc.; five seasons), ‘Safrane’ (Bejo Seeds Inc.; four seasons), and ‘Pocono’ (Seminis Vegetable Seeds Inc., Tifton, GA; two seasons). Unless stated otherwise, onions were treated with 2.26 kg·ha−1 MH (Arysta LifeScience Canada Inc., Guelph, ON). Treatment occurred in the field when 40% to 50% of the tops had fallen 10 to 14 d before harvest. Onions were harvested in mid-September to early October. After harvest, bulbs were cured for 10 to 14 d under a continuous flow of warm dry air. The air temperature was held at 27 to 29 °C for ≈3 d and then lowered to 21 to 24 °C with an RH of 40%. After curing, onions were cooled to ambient temperature with 65% to 70% RH and then transferred to commercial cold storage at 0 to 1 °C and 70% to 75% RH until being placed under experimental storage conditions in late November. For each storage treatment, onions of each cultivar were sampled from three fields. Onions were sampled from different locations within a field in instances where less than three fields of a specific cultivar were available.

To test whether continuous ethylene treatment during storage could replace MH treatments, onion samples were manually harvested in the 2018 and 2019 seasons from sections of fields that were not sprayed with MH as well as adjacent sprayed sections. Cultivars included Pocono (2019) and Safrane (2018 and 2019). Onion samples (22.7 kg) were placed in mesh bags, transferred to a bin, and cured with the rest of the crop.

Storage conditions.

Onions were stored at the Kentville Research and Development Center (Kentville, Canada) from December through August in custom-made top-loading 0.34-m3 stainless steel CA chambers. A tray containing 500 g of CaCl2 was placed in the bottom of each chamber to control RH. Onions were sorted to remove any visibly defective onions and ≈3.6 kg of samples, each comprising 20 to 30 onions, were placed in mesh bags. Four mesh bags (one for each evaluation) for each cultivar/field were placed into bushel plastic bins and bins were placed in storage chambers, which each held four bins and represented a treatment replication. The chambers were flushed with air at 2 L·min−1 for 2 to 3 d before establishing ethylene atmospheres. For ethylene treatments, compressed ethylene gas was mixed with air in a manifold to achieve the desired concentration before introduction to the designated chamber. Chambers were flushed with 2 L·min−1 of air or ethylene in air on a schedule of 6 h on/6 h off to maintain a constant ethylene concentration and flush out CO2. Ethylene concentration was monitored every 2 h using an automated sampling system interfaced with a Shimadzu gas chromatograph with a photoionization detector (GC-8A; Shimadzu Scientific Instruments, Columbia, MD) and an Alumina F1 60/80 mesh packed column (Chromatographic Specialties Inc., Brockville, ON). Chambers were held in a 1 °C cold room. Actual temperature and RH were monitored in chambers using data loggers and temperature in chambers averaged 1.8 ± 0.4 °C and RH averaged 71.6 ± 6.8%.

Treatments.

Each season, onions were stored in air or 7 µL·L−1 ethylene for up to 9 months. Abeles et al. (2012) reported that saturating effects of ethylene were considered to occur at ethylene concentration between 5 and 10 µL·L−1, and Bufler (2009) reported that 7 µL·L−1 ethylene was effective in inhibiting onion sprouting. Therefore, 7 µL·L−1 ethylene was chosen as a standard ethylene treatment concentration and was applied each season.

A delayed ethylene treatment was applied in the 2015, 2016, 2017, 2018, and 2019 seasons, where onions were held in air for the first 4 months and then held in 7 µL·L−1 ethylene for the remainder of storage starting at the beginning of April. To explore the effectiveness of a lower ethylene concentration, in the 2015 season, onions were held in 1 µL·L−1 ethylene for the entire storage period. In the 2018 and 2019 seasons, onions with and without MH treatment were stored in air, 7 µL·L−1 ethylene, or air for 4 months followed by 7 µL·L−1 ethylene (delayed). In the 2020 season, to assess potential shelf life after storage, ‘Patterson’ and ‘Mountaineer’ onions were stored in air or 7 µL·L−1 ethylene, and onions were evaluated immediately after storage or after an additional 4 weeks at ambient conditions, which averaged 20.5 ± 0.9 °C and 65.0 ± 12.2% RH.

Onion evaluation.

Onions were removed from storage for evaluation after 0, 3, 5, 7, and 9 months for each season. At each removal, a subsample of the onions consisting of a mesh bag containing ≈3.6 kg of onions was removed from the treatment chambers and onion bulb quality was assessed. Upon removal, onions were placed under plastic to prevent condensation and held overnight to warm to room temperature. Onions were then weighed to determine weight loss and assessed for the presence of decay and protruding sprouts. Decay caused by both fungal and bacterial pathogens was variable among onion cultivars, fields, and seasons and included Fusarium basal rot, neck rot, sour skin, and soft rot. Some decay was not apparent until bulbs were cut. Any amount of decay was considered unacceptable, and decayed bulbs were counted and discarded. To assess sprout growth, onion bulb height was measured from stem plate to shoulder and the onion was then cut longitudinally, and sprout length was measured from stem plate to tip of the sprout. Bulbs expressing rooting were counted in the 2018 and later seasons. Desiccation of bulbs was not observed, except for those expressing substantial sprouting.

Statistical analysis.

For each season the experimental design for storage was a latinized block, where each block comprised one of the three fields that served as replicates for each cultivar, and storage chambers were assigned to each of the storage treatments. Each of the four totes within a chamber contained four bags of onions, one for each of the four storage removals. Onions in a tote represented one cultivar for one field. Data were analyzed by analysis of variance using Genstat for Windows 21st Edition (VSN International, Hemel Hempstead, UK). A meta-analysis of the combined data from the 2015 to 2020 seasons was conducted using the restricted maximum likelihood procedure in Genstat to provide a robust assessment of the continuous and delayed 7 µL·L−1 ethylene treatments. A mixed-model analysis was used with a meta-structure on seasons. A random model of Year/Chamber.Rep was used with a fixed model of storage treatment × cultivar × removal. Large residuals were removed before analyses and F probabilities <0.05 were considered significant.

Results and Discussion

Sprout elongation in air.

At the beginning of storage, % sprout/bulb length ranged from 32.6% in ‘Copra’ to 44.2% in ‘Mountaineer’ based on the meta-analysis of onions stored over six seasons (Fig. 1). Initial sprout length of ‘Pocono’ and ‘Safrane’ was similar to that of ‘Copra’, whereas that of ‘Patterson’ was similar to ‘Mountaineer’. The % sprout/bulb length of all cultivars increased during 9 months of storage, although there appeared to be a delay in elongation during the first 3 months of storage in ‘Patterson’ and to a lesser degree in ‘Pocono’ and ‘Safrane’ onions. This delay in elongation suggests that the duration of endodormancy varied among the cultivars in this study. The meta-analysis revealed a significant interaction between onion cultivars and storage time (P < 0.001). After 9 months of storage, sprout length increased 132% in ‘Pocono’, followed by ‘Safrane’ (117%), ‘Copra’ (110%), ‘Mountaineer’ (107%), and ‘Patterson’ (87%). Protruding sprouts were not apparent among bulbs from most cultivars until 7 months of storage, when air-stored ‘Mountaineer’ and ‘Pocono’ onions both had more than 9% bulbs with visible sprouts (Fig. 2). After 9 months of storage, the percentage of onions with protruding sprouts was greatest in air-stored onions of the cultivar ‘Mountaineer’ (18.1%), followed by ‘Pocono’ (11.9%), ‘Patterson’ (6.9%), ‘Safrane’ (4.8%), and ‘Copra’ (3.1%).

Fig. 1.
Fig. 1.

The % sprout length relative to the bulb height of ‘Copra’, ‘Mountaineer’, ‘Patterson’, ‘Pocono’, and ‘Safrane’ onions from the 2015 to 2020 seasons during storage at 1 °C for up to 9 months in air, 7 µL·L−1 ethylene or air for 4 months, followed by 7 µL·L−1 ethylene (delayed). Onions were treated with maleic hydrazide in the field before harvest. Error bars represent 2 × se.

Citation: HortScience 57, 6; 10.21273/HORTSCI16547-22

Fig. 2.
Fig. 2.

The % bulbs with protruding sprouts of ‘Copra’, ‘Mountaineer’, ‘Patterson’, ‘Pocono’, and ‘Safrane’ onions from the 2015 to 2020 seasons during storage at 1 °C for up to 9 months in air, 7 µL·L−1 ethylene or air for 4 months followed by 7 µL·L−1 ethylene (delayed). Onions were treated with maleic hydrazide in the field before harvest. Error bars represent 2 × se.

Citation: HortScience 57, 6; 10.21273/HORTSCI16547-22

Sprouting following prolonged storage varied substantially among onion cultivars (Aoba, 1955; Grevsen and Sorensen, 2004; Miedema, 1994). Aoba (1955) reported the cultivar-dependent rate of sprout elongation among three cultivars commenced after 1 to 2 months of normal storage conditions. In a review of onion dormancy, Komochi (1990) concluded the rate of sprout elongation was more important than the length of endodormancy in determining sprout resistance of onions. Brewster (1987) described sprout elongation as a continuous process that accelerated with storage time. We observed that after 3 months of storage, sprout elongation increased at a constant rate ranging from 3.2% to 6.5% per month among the cultivars. ‘Copra’ had the lowest rate of sprout elongation as well as the least number of bulbs with protruding sprouts.

Ethylene.

Sprout growth was reduced in all onions stored in 7 µL·L−1 ethylene atmospheres compared with onions stored in air (Fig. 1). After 9 months of storage, the % sprout/bulb length of onions stored in 7 µL·L−1 ethylene averaged 16.4% to 23.5% less than air-stored onions in the five cultivars studied. Storage in 7 µL·L−1 ethylene also reduced sprout emergence, which after 9 months of storage was 26.1%, 66.7%, 65.5%, 86.1%, and 58.2% less than air stored ‘Copra’, ‘Mountaineer’, ‘Patterson’, ‘Pocono’, and ‘Safrane’ onions, respectively (Fig. 2). This inhibition of sprout growth was previously reported for ‘Copra’ onions held in 7 or 10 ppm ethylene at 18 °C (Bufler, 2009) and ‘Sherpa’ onions held in 10 µL·L−1 ethylene at 1 °C (Alamar et al., 2020; Ohanenye et al., 2019).

When the application of 7 µL·L−1 ethylene was delayed until the end of the fourth month of storage, sprouting was delayed similarly to that observed in the continuous 7 µL·L−1 ethylene treatment in ‘Patterson’ but to a lesser degree in other cultivars (Figs. 1 and 2). After 9 months of storage, the % sprout/bulb length was 7.5%, 11.9%, 13.7%, and 11.1% greater in ‘Copra’, ‘Mountaineer’, ‘Pocono’, and ‘Safrane’ onions subjected to the delayed ethylene treatment compared with those held in continuous 7 µL·L−1 ethylene (Fig. 1). The lack of difference in ‘Patterson’ between the delayed and continuous ethylene treatment may be a result of the endodormancy observed during the first 3 months of storage that was not observed in the other cultivars. The delayed ethylene treatment was also less effective compared with the continuous treatment in suppressing sprout emergence of most cultivars (Fig. 2). After 9 months of storage, onions subjected to the delayed ethylene treatment averaged 3.2%, 1.4%, 3.2%, and 2.4% more bulbs with protruding sprouts in ‘Mountaineer’, ‘Patterson’, ‘Pocono’, and ‘Safrane’, respectively, than in onions subjected to ethylene throughout storage, whereas differences in ‘Copra’ were <1% (P < 0.001). Bufler (2009) also observed that a delayed ethylene treatment reduced sprout elongation and suggested that although the presence of ethylene inhibited elongation, this inhibition was lost when onions were removed from the ethylene atmosphere.

Decay was unaffected by ethylene treatment (Fig. 3). With the exception of ‘Pocono’, decayed onions comprised <7% in all treatments and storage times. After 9 months of storage in 7 µL·L−1 ethylene, decay of ‘Pocono’ bulbs comprised 18% of the bulbs compared with 8.3% of bulbs in air or 9.7% of bulbs held in the delayed ethylene treatment. Ethylene treatments had no significant effect on fresh weight loss during storage. After 9 months of storage, weight loss averaged 8.0%, 7.6%, and 8.8% in air, continuous 7 µL·L−1 ethylene, and delayed 7 µL·L−1 ethylene treatments, respectively.

Fig. 3.
Fig. 3.

The % bulbs with decay of ‘Copra’, ‘Mountaineer’, ‘Patterson’, ‘Pocono’, and ‘Safrane’ onions from the 2015 to 2020 seasons during storage at 1 °C for up to 9 months in air, 7 µL·L−1 ethylene or air for 4 months, followed by 7 µL·L−1 ethylene (delayed). Onions were treated with maleic hydrazide in the field before harvest. Error bars represent 2 × se.

Citation: HortScience 57, 6; 10.21273/HORTSCI16547-22

Ethylene concentration.

In the 2015 season, continuous treatment with 1 µL·L−1 ethylene was compared with 7 µL·L−1 ethylene for three onion cultivars (Fig. 4). Differences in % sprout/bulb length had a significant interaction among cultivars and treatments (P = 0.006), with reduction of sprout elongation by the 1 µL·L−1 ethylene treatment being less in ‘Patterson’ onion than those of ‘Copra’ or ‘Mountaineer’. After 9 months of storage, onions held in 1 µL·L−1 ethylene had 4.0%, 3.5%, and 17.9% greater % sprout/bulb length than those held in 7 µL·L−1 ethylene in ‘Copra’, ‘Mountaineer’, and ‘Patterson’ onions, respectively. The effect of ethylene treatments on protruding sprouts or decay did not differ significantly. Because these preliminary results indicated that 1 µL·L−1 ethylene was less effective in inhibiting sprout elongation than 7 µL·L−1 ethylene, later seasons continued to focus on the 7 µL·L−1 ethylene treatment. Although no other studies report direct comparisons of ethylene concentrations on sprout inhibition, Bufler (2009) treated ‘Copra’ onions with 7.2 or 10.6 µL·L−1 ethylene in different seasons and observed a similar inhibition of sprout growth.

Fig. 4.
Fig. 4.

The % sprout length relative to the bulb height of ‘Copra’, ‘Mountaineer’, and ‘Patterson’ onions from the 2015 season during storage at 1 °C for up to 9 months in air, 1 µL·L−1 ethylene, or 7 µL·L−1 ethylene. Onions were treated with maleic hydrazide in the field before harvest. Error bars represent 2 × se.

Citation: HortScience 57, 6; 10.21273/HORTSCI16547-22

Maleic hydrazide.

In the 2018 and 2019 seasons, onions were harvested both with and without MH treatment and subjected to storage in air or ethylene to assess whether ethylene treatments could be an effective replacement for MH. Sprouting of ‘Safrane’ onions was reduced by both MH and ethylene treatments (Fig. 5). Air-stored onions treated with MH had 22% lower % sprout/bulb length than onions not treated with MH after 9 months of storage. A greater reduction in % sprout/bulb length was observed in onions held in continuous 7 µL·L−1 ethylene in both MH treated and untreated onions, which were 40% and 35% lower than untreated air-stored onions after 9 months of storage, respectively. However, when ethylene treatment was delayed 4 months, sprout growth was greater in onions that were not treated with MH than in those that received the MH treatment.

Fig. 5.
Fig. 5.

The effect of preharvest maleic hydrazide (MH) treatment on % sprout length relative to the bulb height, % bulbs with protruding sprouts, and % bulbs with roots of ‘Pocono’ and ‘Safrane’ onions from the 2018 and 2019 seasons during storage at 1 °C for up to 9 months in air, 7 µL·L−1 ethylene, or air for 4 months, followed by 7 µL·L−1 ethylene (delayed). Error bars represent 2 × se.

Citation: HortScience 57, 6; 10.21273/HORTSCI16547-22

The number of onions with protruding sprouts reflected these effects on sprout growth. MH treatment reduced the number of bulbs with protruding sprouts in ‘Safrane’ onions stored in air and the delayed ethylene treatment. However, onions subjected to continuous ethylene had <2% bulbs with protruding sprout throughout storage regardless of MH treatment (P = 0.013). Rooting of bulbs was also inhibited by both MH and ethylene treatments. The combined treatment of MH and continuous 7 µL·L−1 ethylene totally inhibited root formation in ‘Safrane’ onions. Those treated with only MH or continuous 7 µL·L−1 ethylene had 8% or 13% of bulbs having roots after 9 months of storage, respectively. In contrast, more than 58% of untreated air-stored onions developed roots after 9 months. When ethylene was delayed, 38% of onions not treated with MH developed roots (P = 0.002). Similar results were reported in ‘Sherpa’ onions where storage in 10 µL·L−1 ethylene at 1 °C for 35 weeks resulted in 18% of bulbs forming roots as compared with 63% of air stored bulbs (Cools et al., 2011). Decay and weight loss of stored onions were not significantly affected by the MH or ethylene treatments.

In contrast to ‘Safrane’ onions, sprouting and root growth of untreated ‘Pocono’ onions from the 2019 season remained low during storage. No significant differences between onions treated with MH or ethylene treatments on sprout growth, rooting, or decay were observed (Fig. 5).

Shelf life.

In the 2020 season, quality retention of MH treated ‘Mountaineer’ and ‘Patterson’ onions following storage in air or continuous 7 µL·L−1 ethylene was determined after an additional 4 weeks in air at room temperature, which averaged 20 °C. After three months of storage, the additional four weeks of ambient storage did not significantly increase unmarketable onions, which averaged less than 6% and 7% of ‘Mountaineer’ and ‘Patterson’ onions, respectively (Fig. 6). However, when onions stored for ≥5 months were removed from 1 °C storage and held an additional 4 weeks, the percentage of unmarketable onions increased significantly as a result of increased sprout elongation (P < 0.001), sprout protrusion (P < 0.001), and bulb decay (P < 0.001). Unmarketable onions were significantly less in onions held in 7 µL·L−1 ethylene than those held in air for both ‘Mountaineer’ and ‘Patterson’ due to a reduction in sprout elongation (P = 0.017) and protrusion (P = 0.014). After 7 and 9 months of storage, the percentage of bulbs with protruding sprouts did not increase significantly in the onions held in 7 µL·L−1 ethylene during the additional 4-week shelf-life treatment. In contrast, onions stored in air had 24% to 33% more protruding sprouts than onions that had been stored in 7 µL·L−1 ethylene. However, after 7 or 9 months of storage, onions stored in ethylene developed 7% to 16% more decayed bulbs after 4 weeks at 20 °C than air stored onions. In ‘Patterson’ an increase in decayed bulbs (8%) was also observed immediately after 9 months of storage. Similarly, in the meta-analysis of onion cultivars stored over six seasons, incidence of decay of ‘Pocono’ onions increased after 9 months of storage in 7 µL·L−1 ethylene (Fig. 3). Further assessment of residual effects of ethylene treatment during different ambient shelf-life conditions and durations should be conducted to further assess commercial benefits of ethylene treatments.

Fig. 6.
Fig. 6.

The % sprout length relative to the bulb height, % bulbs with protruding sprouts, % bulbs decayed, and % unmarketable bulbs of ‘Mountaineer’ and ‘Patterson’ onions from the 2020 season during storage at 1 °C for up to 9 months in air or 7 µL·L−1 ethylene with or without an additional 4 weeks in air at 20 °C (shelf life). Onions were treated with maleic hydrazide in the field before harvest. Error bars represent 2 × se.

Citation: HortScience 57, 6; 10.21273/HORTSCI16547-22

Greater levels of both fungal and bacterial decay after prolonged storage in ethylene became apparent after ambient storage and could be a result of ethylene-induced increase in decay susceptibility of the onions. Ethylene stimulates senescence in fruit and vegetative tissues of plants resulting in increased susceptibility to decay (Saltveit, 1999). Previous studies report ethylene enhanced decay incidence and severity in nonclimacteric fruit. The use of ethylene to de-green oranges [Citrus sinensis (L.) Osbeck] increased stem-end rot caused by Diplodia natalensis P. Evans (Brown and Lee Hyoung, 1993) and severity of gray mold in strawberries (Fragaria ×ananassa Duch.) inoculated with Botrytis cinerea Pers.:Fr. (El-Kazzaz et al., 1983). Similarly, removing ethylene from the storage environment reduced strawberry fruit susceptibility to gray mold (Wills and Kim, 1995) and peduncle rot caused by Penicillium in stored pineapples (Ananas comosus L.) (Sabater-Vilar et al., 2018). In contrast, continuous exposure of stone fruit and grapes (Vitis vinifera L.) to ethylene did not increase the incidence or severity of brown rot (Monilinia fructicola) or gray mold (Palou et al., 2003), whereas ethylene induces resistance in Nicotiana benthamiana to Botrytis (Chagué et al., 2006). The prolonged exposure to ethylene in our study may negate any potential beneficial effects in mitigating decay. Ethylene-induced decay appeared to be cultivar dependent and was not observed until after ≥8 months of storage and shelf-life evaluation. Additional assessments may be needed to evaluate whether this observed effect would be a significant concern under commercial onion storage and marketing.

Conclusion

Storage of onions in atmospheres containing ethylene appears to be an effective technology to prolong storage life with acceptable quality being maintained for up to 7 months in all cultivars assessed in this study. An atmosphere of 7 µL·L−1 ethylene was effective in prolonging storage life of MH treated onions by inhibiting sprout elongation and root growth. Although differences in sprout elongation were observed among the five cultivars evaluated in this study, ethylene was effective in reducing sprout elongation in all cultivars. Delaying the application of ethylene by 4 months also delayed sprouting but was not as effective as the continuous treatment. Ethylene provided greater benefit than could be obtained by MH treatments alone and could serve as a replacement for MH. For maximum effectiveness, ethylene exposure must be maintained throughout storage. Furthermore, the residual effectiveness of sprout inhibition on onions stored in 7 µL·L−1 ethylene without MH requires further evaluation.

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  • Lang, G.A. 1987 Dormancy: A new universal terminology HortScience 25 817 820

  • Miedema, P. 1994 Bulb dormancy in onion. I. The effects of temperature and cultivar on sprouting and rooting J. Hort. Sci. 69 29 39 https://doi.org/10.1080/14620316.1994.11515245

    • Search Google Scholar
    • Export Citation
  • Naylor, A.W. & Davis, E.A. 1950 Maleic hydrazide as a plant growth inhibitor Bot. Gaz. 112 112 126

  • Ohanenye, I.C., Alamar, M.C., Thompson, A.J. & Terry, L.A. 2019 Fructans redistribution prior to sprouting in stored onion bulbs is a potential marker for dormancy break Postharvest Biol. Technol. 149 221 234 https://doi.org/10.1016/j.postharvbio.2018.12.002

    • Search Google Scholar
    • Export Citation
  • Pak, C., van der Plas, L.H.W. & de Boer, A.D. 1995 Importance of dormancy and sink strength in sprouting of onions (Allium cepa) during storage Physiol. Plant. 94 277 283 https://doi.org/10.1111/j.1399-3054.1995.tb05312.x

    • Search Google Scholar
    • Export Citation
  • Palou, L., Crisosto, C.H., Garner, D. & Basinal, L.M. 2003 Effect of continuous exposure to exogenous ethylene during cold storage on postharvest decay development and quality attributes of stone fruits and table grapes Postharvest Biol. Technol. 27 243 254 https://doi.org/10.1016/S0925-5214(02)00112-6

    • Search Google Scholar
    • Export Citation
  • Rohde, A. & Bhalerao, R.P. 2007 Plant dormancy in the perennial context Trends Plant Sci. 12 217 223 https://doi.org/10.1016/j.tplants.2007.03.012

  • Sabater-Vilar, M., Suñé-Colell, E., Castro-Chinchilla, J. & Sáenz-Murillo, M.V. 2018 Reduction of postharvest rotting with an ethylene absorbent: A case study with pineapple Acta Hort. 1194 721 728 https://doi.org/10.17660/ActaHortic.2018.1194.103

    • Search Google Scholar
    • Export Citation
  • Saltveit, M.E. 1999 Effect of ethylene on quality of fresh fruits and vegetables Postharvest Biol. Technol. 15 279 292 https://doi.org/10.1016/S0925-5214(98)00091-X

    • Search Google Scholar
    • Export Citation
  • U.S. Department of Agriculture Economic Research Service 2020 Food Availability (Per Capita) Data System—Fruit and Vegetables 16 Nov. 2021. https://www.ers.usda.gov/data-products/food- availability-per-capita-data-system/

    • Search Google Scholar
    • Export Citation
  • Ward, C.M. & Tucker, W.G. 1976 Respiration of maleic hydrazide treated and untreated onion bulbs during storage Ann. Appl. Biol. 82 135 141 https://doi.org/10.1111/j.1744- 7348.1976.tb01680.x

    • Search Google Scholar
    • Export Citation
  • Wills, R.B.H. & Kim, G.H. 1995 Effect of ethylene on postharvest life of strawberries Postharvest Biol. Technol. 6 249 255 https://doi.org/10.1016/0925-5214(95)00005-Q

    • Search Google Scholar
    • Export Citation
  • Yasin, H.J. & Bufler, G. 2007 Dormancy and sprouting in onion (Allium cepa L.) bulbs. I. Changes in carbohydrate metabolism J. Hort. Sci. Biotechnol. 82 89 96 https://doi.org/10.1080/14620316.2007.11512203

    • Search Google Scholar
    • Export Citation

Contributor Notes

We thank Nova Agri Inc. for providing onions and financial support for this research.

Current address for K.C.: Perennia Food and Agriculture Inc., 28 Aberdeen St, Kentville, NS B4N 2N1 Canada

C.F.F. is the corresponding author. E-mail: charles.forney@agr.gc.ca.

  • View in gallery

    The % sprout length relative to the bulb height of ‘Copra’, ‘Mountaineer’, ‘Patterson’, ‘Pocono’, and ‘Safrane’ onions from the 2015 to 2020 seasons during storage at 1 °C for up to 9 months in air, 7 µL·L−1 ethylene or air for 4 months, followed by 7 µL·L−1 ethylene (delayed). Onions were treated with maleic hydrazide in the field before harvest. Error bars represent 2 × se.

  • View in gallery

    The % bulbs with protruding sprouts of ‘Copra’, ‘Mountaineer’, ‘Patterson’, ‘Pocono’, and ‘Safrane’ onions from the 2015 to 2020 seasons during storage at 1 °C for up to 9 months in air, 7 µL·L−1 ethylene or air for 4 months followed by 7 µL·L−1 ethylene (delayed). Onions were treated with maleic hydrazide in the field before harvest. Error bars represent 2 × se.

  • View in gallery

    The % bulbs with decay of ‘Copra’, ‘Mountaineer’, ‘Patterson’, ‘Pocono’, and ‘Safrane’ onions from the 2015 to 2020 seasons during storage at 1 °C for up to 9 months in air, 7 µL·L−1 ethylene or air for 4 months, followed by 7 µL·L−1 ethylene (delayed). Onions were treated with maleic hydrazide in the field before harvest. Error bars represent 2 × se.

  • View in gallery

    The % sprout length relative to the bulb height of ‘Copra’, ‘Mountaineer’, and ‘Patterson’ onions from the 2015 season during storage at 1 °C for up to 9 months in air, 1 µL·L−1 ethylene, or 7 µL·L−1 ethylene. Onions were treated with maleic hydrazide in the field before harvest. Error bars represent 2 × se.

  • View in gallery

    The effect of preharvest maleic hydrazide (MH) treatment on % sprout length relative to the bulb height, % bulbs with protruding sprouts, and % bulbs with roots of ‘Pocono’ and ‘Safrane’ onions from the 2018 and 2019 seasons during storage at 1 °C for up to 9 months in air, 7 µL·L−1 ethylene, or air for 4 months, followed by 7 µL·L−1 ethylene (delayed). Error bars represent 2 × se.

  • View in gallery

    The % sprout length relative to the bulb height, % bulbs with protruding sprouts, % bulbs decayed, and % unmarketable bulbs of ‘Mountaineer’ and ‘Patterson’ onions from the 2020 season during storage at 1 °C for up to 9 months in air or 7 µL·L−1 ethylene with or without an additional 4 weeks in air at 20 °C (shelf life). Onions were treated with maleic hydrazide in the field before harvest. Error bars represent 2 × se.

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  • Lang, G.A. 1987 Dormancy: A new universal terminology HortScience 25 817 820

  • Miedema, P. 1994 Bulb dormancy in onion. I. The effects of temperature and cultivar on sprouting and rooting J. Hort. Sci. 69 29 39 https://doi.org/10.1080/14620316.1994.11515245

    • Search Google Scholar
    • Export Citation
  • Naylor, A.W. & Davis, E.A. 1950 Maleic hydrazide as a plant growth inhibitor Bot. Gaz. 112 112 126

  • Ohanenye, I.C., Alamar, M.C., Thompson, A.J. & Terry, L.A. 2019 Fructans redistribution prior to sprouting in stored onion bulbs is a potential marker for dormancy break Postharvest Biol. Technol. 149 221 234 https://doi.org/10.1016/j.postharvbio.2018.12.002

    • Search Google Scholar
    • Export Citation
  • Pak, C., van der Plas, L.H.W. & de Boer, A.D. 1995 Importance of dormancy and sink strength in sprouting of onions (Allium cepa) during storage Physiol. Plant. 94 277 283 https://doi.org/10.1111/j.1399-3054.1995.tb05312.x

    • Search Google Scholar
    • Export Citation
  • Palou, L., Crisosto, C.H., Garner, D. & Basinal, L.M. 2003 Effect of continuous exposure to exogenous ethylene during cold storage on postharvest decay development and quality attributes of stone fruits and table grapes Postharvest Biol. Technol. 27 243 254 https://doi.org/10.1016/S0925-5214(02)00112-6

    • Search Google Scholar
    • Export Citation
  • Rohde, A. & Bhalerao, R.P. 2007 Plant dormancy in the perennial context Trends Plant Sci. 12 217 223 https://doi.org/10.1016/j.tplants.2007.03.012

  • Sabater-Vilar, M., Suñé-Colell, E., Castro-Chinchilla, J. & Sáenz-Murillo, M.V. 2018 Reduction of postharvest rotting with an ethylene absorbent: A case study with pineapple Acta Hort. 1194 721 728 https://doi.org/10.17660/ActaHortic.2018.1194.103

    • Search Google Scholar
    • Export Citation
  • Saltveit, M.E. 1999 Effect of ethylene on quality of fresh fruits and vegetables Postharvest Biol. Technol. 15 279 292 https://doi.org/10.1016/S0925-5214(98)00091-X

    • Search Google Scholar
    • Export Citation
  • U.S. Department of Agriculture Economic Research Service 2020 Food Availability (Per Capita) Data System—Fruit and Vegetables 16 Nov. 2021. https://www.ers.usda.gov/data-products/food- availability-per-capita-data-system/

    • Search Google Scholar
    • Export Citation
  • Ward, C.M. & Tucker, W.G. 1976 Respiration of maleic hydrazide treated and untreated onion bulbs during storage Ann. Appl. Biol. 82 135 141 https://doi.org/10.1111/j.1744- 7348.1976.tb01680.x

    • Search Google Scholar
    • Export Citation
  • Wills, R.B.H. & Kim, G.H. 1995 Effect of ethylene on postharvest life of strawberries Postharvest Biol. Technol. 6 249 255 https://doi.org/10.1016/0925-5214(95)00005-Q

    • Search Google Scholar
    • Export Citation
  • Yasin, H.J. & Bufler, G. 2007 Dormancy and sprouting in onion (Allium cepa L.) bulbs. I. Changes in carbohydrate metabolism J. Hort. Sci. Biotechnol. 82 89 96 https://doi.org/10.1080/14620316.2007.11512203

    • Search Google Scholar
    • Export Citation
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