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.
Charles F. Forney, Kristen Cue, and Sherry Fillmore
Charles F. Forney*, Jun Song, and Michael A. Jordan
Apple fruit are treatmented with diphenylamine (DPA) in the form of a postharvest dip to prevent the development of storage scald. However, DPA residues have been detected on apples not treated with DPA, which is problematic in markets where DPA residues are not acceptable. The objective of this study was to identify sources of DPA contamination and evaluate the effectiveness of ozone to reduce contamination. Concentrations of DPA in the atmosphere of commercial storage rooms was monitored during the storage season and the adsorption of DPA onto wood and plastic bin material, plastic bin liners, foam insulation, and apple fruit was assessed. DPA was sampled from headspace with solid phase micro extraction using 65 μm polyacrylate micro fibers and analyzed using GC-MS. The effectiveness of gaseous treatments of 300 and 800 ppb ozone to reduce DPA contamination on apple fruit and bin material was also determined. DPA was found to volatilize from treated apples and bins into the storage room air, where it was adsorbed onto storage room walls, bins, bin liners and other fruit. DPA was found in the atmosphere of storage rooms containing apples that were not treated with DPA. Wood and plastic bin material, bin liners, and foam insulation all had a high affinity for DPA and were determined to be potential sources of contamination. Ozone reacted with DPA and following gaseous ozone treatments, off-gassing of DPA from wood and plastic bin material and bin liners was reduced. However, ozone was not effective in removing all DPA in contaminated materials and was ineffective in removing DPA from contaminated apples. Due to the pervasive and persistent nature of DPA, fruit should be handled and stored in facilities where DPA is not used to prevent contamination of fruit.
Jun Song, Lihua Fan, Charles F. Forney, and Michael A. Jordan
Ethanol production and chlorophyll fluorescence were measured as signals of freezing and heat stress in apple fruit. `Cortland' and `Jonagold' apples were held at –8.5 °C for 0, 6, 12 or 24 h (freezing treatments), or at 46 °C for 0, 4, 8 or 12 h (heat treatments). Following treatments, fruit were stored at 0 °C and evaluated after 0, 1, 2, or 3 months. Following storage, fruit samples were kept for 12 h at 20 °C and then analyzed for ethanol production, chlorophyll fluorescence, and visible injury. Severity of flesh browning increased with increasing treatment time for both freezing and heat treatments. Freezing for 24 h and heating for 12 h caused severe flesh browning in both cultivars. Severity of heat-induced browning increased during storage. Increases in ethanol production were apparent 12 h following treatments and reflected the degree of stress-induced fruit injury. After 2 months of storage, ethanol concentrations peaked and were as much as 400-fold greater than that of controls. These stress treatments also reduced ethylene production and chlorophyll fluorescence. The degree of increase in stress-induced ethanol production and decrease in chlorophyll fluorescence correlated with stress-induced injury and could be used to predict the severity of injury that develops during storage. Other volatile production and their relationship to fruit stress will also be discussed.
Jun Song, Lihua Fan, Charles F. Forney, and Michael A. Jordan
Volatile emissions and chlorophyll fluorescence were investigated as potential signals of heat injury for apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] fruit. `McIntosh', `Cortland', `Jonagold', and `Northern Spy' apples were exposed to 46 °C for 0, 4, 8, or 12 hours (heat treatments). Following treatments, fruit were kept at 20 °C and evaluated after 1, 2, 4, or 7 days. Heat treatments induced volatile production including ethanol and ethyl acetate. The 8 and 12 hours heat treatments increased ethanol and ethyl acetate production in all four cultivars by as much as 170- and 11-fold, respectively, 1 day after treatments. Heat treatments also reduced ethylene production and chlorophyll fluorescence. Heat for 12 hours caused serious flesh browning. Among the cultivars investigated, `Northern Spy' and `McIntosh' were most susceptible to heat stress based on the degree of flesh browning. Correlation coefficients of heat stress induced ethanol emission and chlorophyll fluorescence with flesh browning were 0.82 and -0.66, respectively. The nondestructive measurements of ethanol emission and chlorophyll fluorescence have potential to identify stressed fruit with reduced quality or compromised storage life.
D. Mark Hodges, Wendy V. Wismer, and Charles F. Forney
The responses of certain antioxidants in detached leaves of two cultivars of spinach (Spinacia oleracea L.) differing in their senescence rates were assessed during storage in order to explore the significance of these antioxidants in senescence regulation and dynamics. To identify spinach cultivars differing in their senescence rates, 10 cultivars were grown in field plots, harvested at maturity, and their leaves detached and stored at 10 °C in the dark. At the point of harvest (d 0) and on d 5, 8, 12, and 15, samples were analyzed for lipid peroxidation (MDA), chlorophyll loss, and electrolyte leakage. The cultivars were also grown in laboratory growth chambers to corroborate field results. Two cultivars that were consistently identified as having relatively high (Spokane F1) and low (BJ 412 Sponsor) senescence rates were grown in growth chambers for 45 d, harvested at maturity, and their leaves detached and stored as above. At the point of harvest (d 0) and on d 4, 8, 12, 16, and 20, samples were analyzed for (i) activities of ascorbate peroxidase (ASPX; EC 184.108.40.206), catalase (CAT; EC 220.127.116.11), and superoxide dismutase (SOD; EC 18.104.22.168), and (ii) concentrations of MDA, total ascorbate, reduced ascorbate (AsA), oxidized ascorbate (DAsA), total glutathione, reduced glutathione (GSH) and oxidized glutathione (GSSG). Although MDA accumulated in leaves of both cultivars concomitant with time after detachment, levels became significantly higher in Spokane. Activities of ASPX declined in Spokane leaves following detachment but activities of SOD and levels of glutathione increased in this cultivar. GSH/GSSG increased in `Sponsor', but dramatically more so in `Spokane'. Ascorbate concentrations did not diminish in leaves of `Spokane' to the degree that they did in `Sponsor' tissue. DAsA/AsA values did not decrease in `Spokane' leaves following detachment, though they did in those of `Sponsor'. It is argued that declining activities of ASPX and levels of ascorbate and increasing activities of SOD manifested in accumulation of hydrogen peroxide in Spokane, leading to a greater potential for lipid peroxidation in this variety than for Sponsor. SOD activities and glutathione levels may have increased as a result of elevated oxidative stress in Spokane. Increased hydrogen peroxide accumulation in `Spokane' relative to `Sponsor' may have contributed to an increased rate of senescence in the leaves of this cultivar.
D. Mark Hodges, Charles F. Forney, and Wendy V. Wismer
The objective of this study was to assess responses of certain antioxidants in harvested leaves of selected cultivars of spinach (Spinacia oleracea L.) differing in postharvest senescence rates in order to explore the significance of these antioxidants in postharvest senescence regulation and dynamics. Ten cultivars were grown in both field plots and laboratory growth chambers, harvested at maturity, and their leaves detached and stored at 10 °C in the dark. Following postharvest analysis, two cultivars were identified consistently as having relatively high (`Spokane F1') and low (`BJ 412 Sponsor') postharvest senescence rates. These two cultivars were then grown in a growth chamber for 45 days and their leaves detached and stored as above. At the point of harvest (day 0) and on days 4, 8, 12, 16, and 20, samples were analyzed for activities of ascorbate peroxidase (ASPX; EC 22.214.171.124), catalase (CAT; EC 126.96.36.199), and superoxide dismutase (SOD; EC 188.8.131.52), and (ii) concentrations of malondialdehyde (MDA, an indicator of lipid peroxidation), total ascorbate, reduced ascorbate (AsA), oxidized ascorbate (DAsA), total glutathione, reduced glutathione (GSH), and oxidized glutathione (GSSG). Although MDA accumulated in leaves of both cultivars concomitant with time after detachment, levels became significantly higher in `Spokane F1'. It is argued that declining activities of ASPX and levels of ascorbate and increasing activities of SOD manifested in accumulation of hydrogen peroxide in `Spokane F1', leading to a greater potential for lipid peroxidation in this cultivar than for `BJ 412 Sponsor'. SOD activities and glutathione levels may have increased as a result of elevated oxidative stress in `Spokane F1'. Increased hydrogen peroxide accumulation in `Spokane F1' relative to `BJ 412 Sponsor' may have contributed to an increased rate of senescence in the harvested leaves of this cultivar.
ZhaoSen Xie, Charles F. Forney, WenPing Xu, and ShiPing Wang
In this study, the ultrastructure of phloem and its surrounding parenchyma cells in the developing grape berry produced under root restriction or without (control) was for the first time systematically investigated through transmission electron microscopy during the entire developmental process of the berry. The results showed that root restriction increased the number of plasmodesmata between sieve elements (SE) and companion cells (CC) and between the SE/CC complex and phloem parenchyma cells. Sieve elements in fruit produced under root restriction were smaller in size than those from the control treatment, but CC were bigger than in the control treatment. During the first rapid growth phase of the grape berry, there was denser cytoplasm in the CC produced under root restriction having more abundant mitochondria, endoplasmic reticulum, multivesicular bodies, vesicles, and plastids than in control fruit. During the second rapid growth phase of the grape berry, CC under root restriction showed more serious plasmolysis. Cytoplasmic contents such as vesicles were fused into the vacuole of which the tonoplast nearly disappeared in the phloem parenchyma cells, and cytoplasmic contents in fruit cells produced under root restriction became denser than the control treatment. These results demonstrated that grape berry adapted to the root restriction stress through ultrastructure variation of the phloem, and this variation explained the increase of photosynthate accumulation in the grape berry observed under root restriction.
Orville Osmicote, Charles F. Forney, Jeffrey Richards, and Chiam Liew
Jun Song, Lihua Fan, Paul D. Hildebrand, and Charles F. Forney
The biological effect of corona discharge on onions (Allium cepa L.) in a commercial storage was investigated. Surface discoloration and mold were modestly but significantly reduced by the corona discharge when onions were stored for 2 or 4 weeks with or without an additional 2 weeks of shelf life under high humidity. Corona discharge treatment also reduced airborne mold spores in the storage room. No significant changes in internal decay, firmness, sprouting, or rooting, in treated onions were found.
Charles F. Forney, Stephanie Bishop, Michele Elliot, and Vivian Agar
Extending the storage life of fresh cranberries (Vaccinium macrocarpon Ait.) requires an optimum storage environment to minimize decay and physiological breakdown (PB). To assess the effects of relative humidity (RH) and temperature on storage life, cranberry fruit from four bogs were stored over calcium nitrate, sodium chloride, or potassium nitrate salts, which maintained RH at 75%, 88%, and 98%, respectively. Containers at each RH were held at 0, 3, 5, 7, or 10 °C and fruit quality was evaluated monthly for 6 months. Both decay and PB increased with increasing RH in storage. After 6 months, 32%, 38%, and 54% of fruit were decayed and 28%, 31%, and 36% developed PB when stored in 75%, 88%, and 98% RH, respectively. The effects of RH continued to be apparent after fruit were removed from storage, graded, and held for 7 days at 20 °C. The decay of graded fruit after 4 months of storage in 75%, 88%, or 98% RH was 10%, 13%, and 31%, respectively, while PB was 12%, 12%, and 17%, respectively. Fresh weight loss decreased as RH increased averaging 1.9%, 1.4%, and 0.7% per month for storage in 75%, 88%, and 98% RH, respectively. Fruit firmness was not affected by RH. Storage temperature had little effect on decay. However, PB was greatest in fruit stored at 10 °C, encompassing 55% of fruit after 5 months of storage. When graded fruit were held an additional 7 days at 20 °C, decay and PB were greater in fruit previously stored at 0 or 3 °C than at 5, 7, or 10 °C. Fresh weight loss increased as storage temperature increased, averaging 0.8%, 1.0%, 1.3%, 1.7%, and 1.9% per month at 0, 3, 5, 7, and 10 °C, respectively. Fruit firmness decreased during storage, but was not affected by storage temperature. To maximize storage and shelf life, cranberry fruit should be stored in a RH of about 75% at 5 °C.