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 and Patrick J. Breen
Fruit of strawberry (Fragaria ×ananassa Duch. ‘Brighton’) were removed, and pedicels attached to plants were placed in ethylenediaminetetraacetate (EDTA) to collect phloem sap. The rate of sugar exudation increased with the size of the fruit, but was lower than the rate of dry matter accumulation of the fruit at the time of its removal. When plants were fed 14CO2, radioactivity appeared in the phloem sap after 3 hr, and the rate of exudation of labeled assimilate was maintained at a fairly constant rate for 6 hr. About 92% of the radioactivity in the exudate was in the sucrose fraction, with the remaining in glucose (2%), fructose (1%), and acidic and basic fractions (4%). The results indicate that sucrose is the major assimilate translocated to the fruit.
Charles F. Forney and Breen Patrick J.
Sucrose was not detected in developing fruit of ‘Brighton’ strawberry (Fragaria × ananassa Duch.) until 10 days after anthesis. Thereafter, its concentration increased rapidly but then declined as fruit became red ripe. The concentration of glucose and fructose were similar and higher than that of sucrose during early fruit growth and in ripe fruit. Uptake of 14C-sugars was followed in excised disks of cortical tissue from fruit 15–17 days old. The addition of CaCl2 was necessary to maintain tissue respiration. Sucrose uptake into tissue disks was nearly constant over 4 hr and had a pH optimum of 5.0. Kinetic analysis of sucrose uptake revealed both linear and saturable components. The kinetic characteristics of fructose uptake was similar to those for sucrose. Glucose, however, was taken up much more rapidly than either sucrose or fructose and only demonstrated saturation kinetics. The metabolic inhibitors NaCN (5 mM), dinitrophenol (DNP, 3 Mm) and carbonyl cyanide m-chlorophenyl hydrazone (CCCP, 100 μM) stimulated sucrose uptake 34%, 94%, and 54%, respectively. DNP eliminated the saturable component. Uptake of sucrose was inhibited by 36% with 10 μm DNP, 16% with 5 mM glucose, and 16% in a 100% N2 atmosphere. After incubation in 14C-sugars for 2 hr, about 90% of the label recovered from disks was in a neutral fraction. Half or more of this was in either glucose or fructose, depending upon the sugar fed. The distribution of 14C between glucose and fructose moieties of sucrose isolated from tissue fed (14C-fructosyl) sucrose indicated that a portion of the sucrose recovered underwent hydrolysis and randomization. Similar results were found with sucrose isolated from attached, whole fruit 8 hr after abraded leaves were fed labeled sugars. Results suggest that sucrose may be hydrolized prior to uptake into fruit tissue.
Charles F. Forney and Rodney K. Austin
Concentrations of starch and sugars were measured in the cap leaf (leaf no. 1) and in every fifth leaf (5, 10, 15, 20) in heads of crisphead lettuce (Lactuca sativa L.) harvested at 0700 hr (AM) or 1400 hr (PM) PDT. Starch content increased in the cap leaf from the AM to the PM harvest, but remained unchanged in other leaves. Sucrose concentration was <5 mg·g−1 dry weight in AM-harvested lettuce, but the cap leaf, leaf 20, and stem tissue contained 43, 24, and 61 mg·g−1 dry weight, respectively, in lettuce from the PM harvest. AM harvested lettuce contained 70% to 260% more glucose and 20% to 120% more fructose than PM-harvested lettuce. Glucose and fructose concentrations were greatest in leaf 10 (110 and 120 mg·g−1 dry weight, respectively) and decreased 20% to 50% in inner and outer leaves. Exposure of lettuce to 7.5% or 10% CO2 for 12 days at 2.5°C followed by air for 3 days at 10° caused more severe injury on AM- than on PM-harvested lettuce. Injury occurred primarily on leaves 7 through 17, with those between leaves 10 and 15 being most severely affected. High reducing sugar content at harvest did not appear to decrease the sensitivity of lettuce to high CO2 during storage.
Charles F. Forney and Patrick J. Breen
Day-neutral strawberries (Fragaria × ananassa Duch. ‘Brighton’) were grown in a greenhouse and either continuously deblossomed or allowed to fruit over a 50 day period. Total plant dry weight was essentially the same in both treatments throughout this period. During a 25-day-period, the fruit truss was the predominant sink and, for about 9 days, fruit growth rate exceeded that of the whole plant, and the growth rates of other plant parts were reduced to zero. At the end of the study, fruiting plants had accumulated 16 g dry weight in fruit and had 62%, 53%, and 44% less dry matter in roots, crown, and leaf blades than deblossomed plants. The starch content of roots, crown, and leaf blades of deblossomed plants was about 18-, 7- and 4-times higher than plants with fruit. Fruiting reduced stolon, inflorescence, and branched crown emergence by 80% or more. Leaf area was not affected significantly by treatments, but specific leaf weight of deblossomed plants was as much as 44% higher than that of fruiting plants. Fruiting did not have a significant effect on unit leaf rate. Net photosynthetic rates of leaves which emerged with the 1st inflorescence were similar in both treatments before rapid fruit growth; thereafter, photosynthesis of comparable leaves was 60% to 80% higher in fruiting than deblossomed plants. The presence of fruit also increased stomatal and mesophyll conductance by 40%. The increase in root system in a finite soil volume may have affected assimilation by deblossomed plants adversely. These results show that strawberry fruit strongly inhibit starch accumulation and growth of vegetative parts, while maintaining or enhancing photosynthesis.
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.